Cadmium toxicity in Salvia sclarea L.: An integrative response of element uptake, oxidative stress markers, leaf structure and photosynthesis

Smart reprogramming of plants against cadmium toxicity using membrane transporters and modern tools

Cadmium (Cd) in soil and water streams is now recognized as a significant environmental issue that harms plants and animals. Plants damaged by Cd toxicity experience various effects, from germination to yield reduction. Plant- and animal-based goods are allowing more Cd to enter our food chain, which could harm human health. Therefore, this urgent global concern must be addressed by implementing appropriate remedial measures. Plant-based phytoremediation is one safe, economical, and environmentally acceptable way to remove hazardous metals from the environment. Hyperaccumulator plants possess specialized transport proteins, such as metal transporters located in membranes of roots, as well as they facilitate Cd uptake from soil. This review outlines the latest findings about these membrane transporters. Moreover, we also discuss how innovative modern tools such as microbiomes, omics, nanotechnology, and genome editing have revealed molecular regulators connected to Cd tolerance, which may be employed to develop Cd-tolerant future plants. We can develop effective solutions to enhance tolerance of plant to Cd toxicity by leveraging membrane transporters and modern biotechnological tools. Additionally, implementing strategies to increase tolerance of Cd and restrict its bioavailability in plants' edible parts is crucial for improving food safety. These combined efforts will lead to the cultivation of safer food crops and support sustainable agricultural practices in contaminated environments.

Hormesis effect of cadmium on pakchoi growth: Unraveling the ROS-mediated IAA-sugar metabolism from multi-omics perspective

Previous research on cadmium (Cd) focused on toxicity, neglecting hormesis and its mechanisms. In this study, pakchoi seedlings exposed to varying soil Cd concentrations (CK, 5, 10, 20, 40 mg/kg) showed an inverted U-shaped growth trend (hormesis characteristics): As Cd concentration increases, biomass exhibited hormesis character (Cd5) and then disappear (Cd40). ROS levels rose in both Cd treatments, with Cd5 being intermediate between CK and Cd40. But Cd5 preserved cellular structure, unlike damaged Cd40, hinting ROS in Cd5 acted as signaling regulators. To clarify ROS controlled subsequent metabolic processes, a multi-omics study was conducted. The results revealed 143 DEGs and 793 DEMs across all Cd treatment. KEGG indicated among all Cd treatments, the functional differences encompass: "plant hormone signal transduction" and "starch and sucrose metabolism". Through further analysis, we found that under the influence of ROS, the expression of IAA synthesis and signaling-related genes was significantly up-regulated, especially under Cd5 treatment. This further facilitated the accumulation of reducing sugars, which provided more energy for plant growth. Our research results demonstrated the signaling pathway involving ROS-IAA-Sugar metabolism, thereby providing a novel theoretical basis for cultivating more heavy metal hyperaccumulator crops and achieving phytoremediation of contaminated soils.

Effects of cadmium (Cd) on photosynthetic characteristics and chlorophyll fluorescence parameters in the ornamental Plant Salvia splendens Ker-Gawl

Salvia splendens Ker-Gawl. (scarlet sage), widely used in urban landscaping, it is frequently exposed to cadmium (Cd) contamination resulting from industrial and vehicular emissions. However, its tolerance and adaptability to Cd stress remain poorly understood. A soil experiment was conducted to investigate the effects of Cd on the growth and the photosynthetic performance of S. splendens by measuring photosynthetic pigments, gas exchange and chlorophyll fluorescence parameters. Four weeks-seedlings were treated with 0 (CK), 0.5, 2.5, 5, 10, 25 and 50 mg·kg-1 Cd for 60 days. Results showed significant reductions in root length and biomass of leaves, stems, and roots, with shoot and root biomass notably decreasing by up to 46.3% and 28.5% at higher Cd levels, respectively. The translocation factor remained low (TF < 1.0), and the bioaccumulation factors (BCF < 1.0) decreased when Cd higher than 5 mg·kg-1, indicating limited Cd uptake. Cd stress (> 5 mg·kg-1) caused a decrease in Chl a and Chl b content, but increased the Chl a/b ratio, thereby disrupting photosynthesis and causing significant declines in photosynthetic parameters. Cd exposure (> 2.5 mg·kg-1) significantly decreased net photosynthetic rate (Pn) by 18.94-52.91%, stomatal conductance (Gs) by 35.77-58.53%, and transpiration rate (Tr) by 24.63-48.83%, accompanied by only a slight reduction in inter-cellular CO2 concentration (Ci) of just 7.0%, indicating non-stomatal factors in Pn decline. Cd concentrations (> 5 mg·kg-1) caused a reduction in initial fluorescence (Fo) by 7.44-31.58% and maximal fluorescence (Fm) measurements by about 20%, indicating damage to photosystem II (PSII). At 50 mg·kg-1, further decreases were observed in photochemical quenching (qP) by 40.31%, the quantum yield of photochemical energy dissipation (ΦPSII) by 44.77%, and the electron transport rate (ETR) by 25.11%, while non-photochemical quenching increased by 42.66%, signifying significant PSII inhibition and enhanced photoinhibition. Decrease in ΦPSII, along with the increase in the quantum yield of regulated non-photochemical energy loss in PSII (ΦNPQ) and the quantum yield of non-regulated energy loss in PSII (ΦNO) as Cd levels rise, indicates enhanced non-photochemical energy dissipation and greater photoinhibition. S. splendens shows high sensitivity to Cd stress, with reduced growth and disrupted photosynthesis, highlighting its potential as a bioindicator for Cd contamination in urban areas.

Synergistic effect of mulch and nitrogen management on growth and essential oil yield of Salvia sclarea L

Balanced plant nutrition and optimal micro-climate are critical for achieving higher production sustainably. Substituting mineral fertilizers with organic amendments under water-conserving strategies like mulch can enhance the quality and yield and improve soil health. Therefore, a two-year study was conducted to examine the synergistic effects of mulch and reducing inorganic fertilizers and partially substituting organic amendments on essential oil (EO) yield and its composition, and soil properties in Salvia sclarea, an industrially important crop. Two mulching practices (M1: without mulch; M2: with mulch) and five nitrogen (N) management practices [N1: control; N2: 100% recommended dose of N i.e.,120 kg/ha; N3: 25% N through chemical fertilizer (CF) + 75% N through farm yard manure (FYM); N4: 50% N through CF + 50% N through FYM, N5: 75% N through CF + 25% N through FYM] were taken as experimental treatments, with a total of ten treatment combinations in a split-plot design during 2021-22 and 2022-23. The results showed that applying mulch increased the plant height, leaf area index (LAI), and EO yield. Among N management practices, N2 outperformed for all the morpho-physiological and yield parameters studied except stem diameter and produced at par outcomes with N5 in case of flower spike per plant, LAI, chlorophyll a and b, flower spike yield, EO content and yield. Optimum soil temperature and moisture under mulching modulate the nutrient concentration; similarly, N being necessary for photosynthesis, translocation of nutrients, enzymatic activity, and vegetative and reproductive growth, synergistically enhanced the EO yield and altered the composition. The heat map displayed an inconsistent pattern of the treatment combination's impact on EO components. In soil properties, treatment N5 recorded highest value of available N at 0-0.15 m soil depth; however, at 0.15-0.30 m, N2 registered a higher value and produced at par results with N5. In case of potassium and soil organic carbon, T3 recorded higher value, followed by T4 and T5 at 0-0.15 m. Considering the soil health and without compromising the EO yield much, the present study suggested replacing 25% of recommended chemical N with organic manures under mulch for sustainable and economical production of S. sclarea.

Arbuscular Mycorrhizal Fungi-Assisted Phytoremediation: A Promising Strategy for Cadmium-Contaminated Soils

Arbuscular mycorrhizal fungi (AMF) have been shown to play a major role in regulating the accumulation, transport, and toxicity of cadmium (Cd) in plant tissues. This review aims to highlight the current understanding of the mechanisms by which AMF alleviate Cd toxicity in plants. Cd accumulation in agricultural soils has become an increasing global concern due to industrial activities and the use of phosphatic fertilizers. Cd toxicity disrupts various physiological processes in plants, adversely affecting growth, photosynthesis, oxidative stress responses, and secondary metabolism. AMF alleviate Cd stress in plants through multiple mechanisms, including reduced Cd transport into plant roots, improved plant nutritional status, modulation of organic acid and protein exudation, enhanced antioxidant capacity, and maintenance of ion homeostasis. AMF colonization also influences Cd speciation, bioavailability, and compartmentalization within plant tissues. The expression of metal transporter genes, as well as the synthesis of phytochelatins and metallothioneins, are modulated by AMF during Cd stress. However, the efficacy of AMF in mitigating Cd toxicity depends on several factors, such as soil properties, plant species, AMF taxa, and experimental duration. Further knowledge of the intricate plant-AMF-Cd interactions is crucial for optimizing AMF-assisted phytoremediation strategies and developing Cd-tolerant and high-yielding crop varieties for cultivation in contaminated soils.

Effect of Ag+ and Cd2+ Elicitation on Polyphenol Production in Shoot Culture of Dracocephalum ruyschiana L

Abiotic elicitation with heavy metals has demonstrated considerable potential to stimulate the production of industrially important secondary metabolites in plant in vitro cultures. The present study investigates the effect of exogenous silver nitrate and cadmium chloride supplementation on flavonoid and phenolic acid production, as well as other indicators of oxidative stress, in shoot cultures of Dracocephalum ruyschiana L. Owing to the presence of bioactive polyphenolic compounds, this Mongolian medicinal plant is traditionally used as an anti-inflammatory, antibacterial and antipyretic agent. The shoots were cultured for three weeks, and then, cadmium (Cd2+) and silver (Ag+) ions (50 or 100 µM) were added to the medium. The maximum proliferation rate was observed in the presence of 100 µM Ag+ (almost 5), the highest chlorophyll content in the presence of 100 µM Cd2+ (0.6 mg/g FW) and the highest biomass was observed with both these treatments (73.4-75.7 g FW and 7.53-7.72 g DW). UPLC-PDA-ESI-MS analysis revealed four phenolic acids and five flavonoid derivatives in the hydromethanolic extract of D. ruyschiana shoots. All treatments stimulated the production of rosmarinic acid (RA), which was the dominant compound in the analyzed culture; the highest level of RA, i.e., about three times higher than the control, was noted in shoots exposed to 50 µM Cd2+ (14.72 mg/g DW), whereas the level of most flavonoids in the culture increased most significantly when exposed to Cd2+ at a concentration of 100 µM. Moreover, the shoots grown in the presence of 100 µM Cd2+ exhibited significantly higher antioxidant potential in comparison to the control. Our findings indicate that heavy metals are able to stimulate phenolic compound biosynthesis in Dracocephalum shoots without any negative impact on their growth. These results could be of significant importance for the medical, nutraceutical and agronomic industries.

Physiological and biochemical responses in a cadmium accumulator of traditional Chinese medicine Ligusticum sinense cv. Chuanxiong under cadmium condition

Ligusticum sinense cv. Chuanxiong (L. Chuanxiong), one of the widely used traditional Chinese medicines (TCM), is currently facing the problem of excessive cadmium (Cd) content. This problem has significantly affected the quality and safety of L. Chuanxiong and become a vital factor restricting its clinical application and international trade development. Currently, to solve the problem of excessive Cd, it is essential to research the response mechanisms of L. Chuanxiong to Cd stress. However, there are few reports on its physiological and biochemical responses under Cd stress. In this study, we conducted the hydroponic experiment under 25 μM Cd stress, based on the Cd content of the genuine producing areas soil. The results showed that 25 μM Cd stress not only had no significant inhibitory effect on the growth of L. Chuanxiong seedlings but also significantly increased the chlorophyll a content (11.79%) and root activity (51.82%) compared with that of the control, which might be a hormesis effect. Further results showed that the absorption and assimilation of NH4+ increased in seedlings under 25 μM Cd stress, which was associated with high photosynthetic pigments. Here, we initially hypothesized and confirmed that Cd exceedance in the root system of L. Chuanxiong was due to the thickening of the root cell wall, changes in the content of the cell wall components, and chelation of Cd by GSH. There was an increase in cell wall thickness (57.64 %) and a significant increase in cellulose (25.48%) content of roots under 25 μM Cd stress. In addition, L. Chuanxiong reduced oxidative stress caused by 25 μM Cd stress mainly through the GSH/GSSG cycle. Among them, GSH-Px (48.26%) and GR (42.64%) activities were significantly increased, thereby maintaining a high GSH/GSSG ratio. This study preliminarily reveals the response of L. Chuanxiong to Cd stress and the mechanism of Cd enrichment. It provides a theoretical basis for solving the problem of Cd excessive in L. Chuanxiong.

Enhancing physio-biochemical characteristics in okra genotypes through seed priming with biogenic zinc oxide nanoparticles synthesized from halophytic plant extracts

Poor seedling germination and growth can result in large financial losses for farmers, thus, there is an urgent need for sustainable agricultural techniques to enhance seed germination and early growth. As an outcome, sustainable agriculture-which emphasizes the smart and effective utilization of resources-has gained popularity worldwide. At numerous levels, the field of nanotechnology is capable of significant benefit in achieving sustainable agricultural practices. Zinc oxide nanoparticles (ZnO NPs) have been shown to have biostimulatory properties and serve as effective solutions for addressing environmental and biotic stressors. The purpose of this study, investigating Salvadora persica halophytic leaf extract -synthesized zinc oxide nanoparticles (S-ZnONPs) as nano-priming agents to ensure okra seeds germinated under stress-free conditions. From an application perspective, we examined the effect of seed priming with varying concentrations of S-ZnO NPs (0, 20 and 40 ppm) for 18 and 24 h of soaking. Results indicated that the germination rate of hybrid variety improved with 20 ppm at 18 h, increasing by 58.22%, while mean germination time reduced by 24.62%. An enhancement trend was observed in the shoot, root length, shoot and root fresh weight, shoot and root dry weight of hybrid variety at 20ppm with 18 h priming by 34.2, 84.3, 80.2, 47.4, 50.3, and 36.2%, respectively. However, chlorophyll pigments chl a, chl b, and carotenoids was significantly raised in desi variety by 42.4, 79.31, and 142.29% with 20 ppm at 18 h priming. Hydrogen per oxide decreased up to 87.8% with 40 ppm at 24 h in hybrid variety, while, in desi variety H2O2 was reduced 88.3% with 20 ppm at 24 h. Non enzymatic antioxidant activities such as ascorbic acid, was highly increased 130.6% in hybrid at 24 h priming with 20 ppm dose. Flavonoids raised in same variety by 166.1% with 20 ppm at 18 h. Proline content was increased by 144.5% with 40ppm at 18 h. Moreover, Antioxidant enzymes, superoxide dismutase, peroxidase and catalase were significantly increased in both varieties with both levels of S-ZnO NPs and priming time. This cost-effective and environmentally safe technique to produce nanoparticles of different halophytic plants can maximize resource utilization, supporting sustainable agriculture by minimizing adverse environmental effects without compromising efficiency.

Interactive effect of 24-epibrassinolide and silicon on the alleviation of cadmium toxicity in rice (Oryza sativa L.) plants

Cadmium (Cd) pollution is a serious threat to food safety and human health. Minimization of Cd uptake and enhancing Cd tolerance in plants are vital to improve crop yield and reduce hazardous effects to humans. In this study, we investigate the effect of a synergistic system with phytohormone (24-Epibrassinolide, EBL) and silicon (Si) on Cd toxicity and accumulation of rice plants. The results revealed that Si, EBL and their combination rescued Cd-induced growth inhibition, as evidenced by the increased dry weight of root and shoot. The chlorophyll content and photosynthetic performance were improved. The activity of antioxidant enzymes (SOD, POD and CAT) was increased and oxidative stress was alleviated. More importantly, Cd content in root was decreased by 20.25%, 17.72% and 27.84%, while Cd content in shoot decreased by 21.17%, 16.47% and 25.88%, respectively. Moreover, Si, EBL and Si + EBL treatment enriched cell wall-bound Cd and reduced Cd toxicity to functional organelles. Meanwhile, the residual form of Cd was enriched and the highly toxic forms of Cd (inorganic and water-soluble Cd) were decreased. The joint application showed better effects than applying Si and EBL alone. Collectively, this study provides an effective way for Cd toxicity mitigation in rice plants.

Chemometrics-based analysis of the phytochemical profile and antioxidant activity of Salvia species from Iran

In recent years, the exploration of the therapeutic potential of Salvia has gained considerable attention, leading to a growing number of scientific studies emphasizing its pharmacological properties. Despite this, therapeutic applications of Salvia remain underexploited, requiring further investigation. Iran is a major center for sage diversity in Asia, boasting 60 Salvia species, 17 of which are unique to the area. This study aimed to comprehensively explore and compare the extracts of 102 Salvia samples belonging to 20 distinct Salvia species from Iran, providing a deeper understanding of their specific polyphenol content and, consequently, their antioxidant capabilities and potential therapeutic uses. All samples were analyzed to determine the contents of total phenolics, total flavonoids, total tannin, photosynthetic pigments, and ascorbic acid, along with their antioxidant activity. These data were then combined with the forty distinct chemical fingerprints identified by ultrafast high-pressure liquid chromatography coupled with high-resolution mass spectrometry. Multivariate data analysis was employed to find correlations and differences among the huge number of data obtained and to identify Salvia species with similar phytochemical and/or antioxidant properties. The results show that each Salvia species is characterized by a distinct class of polyphenols recognized for their antidiabetic, anti-inflammatory, cardioprotective and neuroprotective properties. Overall, our findings reveal the potential of some Salvia species for targeted therapeutic applications and provide a rational basis for the development of Salvia-derived nutraceuticals, ultimately improving the prospects for the use of Salvia in medicine.

Copper oxide nanoparticles mitigate cadmium toxicity in rice seedlings through multiple physiological mechanisms

Heavy metal pollution poses a serious threat to crops growth and yield. Recently, nanoparticles (NPs) have emerged as a promising strategy to mitigate the negative effect of heavy metal on crop growth. This study investigated the beneficial effects of copper oxide nanoparticles (CuO NPs) on the morphological and physiological-biochemical traits of rice seedlings (Oryza sativa L.) under cadmium (Cd) stress. The results demonstrated that the application of CuO NPs increased the contents of nutrition elements in shoots and roots as well as photosynthetic pigments, consequently improving the growth of rice seedlings under Cd stress, especially at low level of Cd stress. Meanwhile, CuO NPs obviously decreased the Cd accumulation in the rice seedlings and immobilized Cd in less toxic chemical forms and subcellular compartments. Moreover, CuO NPs modulated the antioxidant system, ameliorating oxidative damage and membrane injury caused by Cd. Multivariate analysis established correlations between physio-biochemical parameters and further revealed the mitigation of Cd damage to rice seedlings by CuO NPs was associated with inhibition Cd accumulation, altering Cd chemical form and subcellular distribution, increasing the contents of mineral nutrients, photosynthetic pigments and secondary metabolites and antioxidant enzyme activities, and reducing oxidative damage. Overall, the present study indicated that CuO NPs could effectively reduce the Cd toxicity to rice seedlings, demonstrating their potential application in agricultural production.

Effects of Cadmium Stress on Tartary Buckwheat Seedlings

Cadmium (Cd) is a naturally occurring toxic heavy metal that adversely affects plant germination, growth, and development. While the effects of Cd have been described on many crop species including rice, maize, wheat and barley, few studies are available on cadmium's effect on Tartary buckwheat which is a traditional grain in China. We examined nine genotypes and found that 30 µM of Cd reduced the root length in seedlings by between 4 and 44% and decreased the total biomass by 7 to 31%, compared with Cd-free controls. We identified a significant genotypic variation in sensitivity to Cd stress. Cd treatment decreased the total root length and the emergence and growth of lateral roots, and these changes were significantly greater in the Cd-sensitive genotypes than in tolerant genotypes. Cd resulted in greater wilting and discoloration in sensitive genotypes than in tolerant genotypes and caused more damage to the structure of root and leaf cells. Cd accumulated in the roots and shoots, but the concentrations in the sensitive genotypes were significantly greater than in the more tolerant genotypes. Cd treatment affected nutrient uptake, and the changes in the sensitive genotypes were greater than those in the tolerant genotypes, which could maintain their concentrations closer to the control levels. The induction of SOD, POD, and CAT activities in the roots and shoots was significantly greater in the tolerant genotypes than in the sensitive genotypes. We demonstrated that Cd stress reduced root and shoot growth, decreased plant biomass, disrupted nutrient uptake, altered cell structure, and managed Cd-induced oxidative stress differently in the sensitive and tolerant genotypes of Tartary buckwheat.

Graphitic carbon nitride nanosheets mitigate cadmium toxicity in Glycine max L. by promoting cadmium retention in root and improving photosynthetic performance

Cadmium (Cd) pollution poses a serious threat to plant growth and yield. Nanomaterials have shown great application potential for alleviation of Cd toxicity to plants. In this study, we applied graphitic carbon nitride nanosheets (g-C3N4 NSs) for alleviation of Cd-toxicity to soybean (Glycine max L.). The g-C3N4 NSs supplementation significantly improved plant growth and reduced oxidative damage in the Cd-toxicated soybean seedlings through hydroponic culture. Particularly, the g-C3N4 NSs dynamically regulated the root cell wall (RCW) components by increasing pectin content and modifying its demethylation via enhancing pectin methylesterase (PME) activity, therefore greatly enhanced stronger RCW-Cd retention (up to 82.8%) and reduced Cd migration to the shoot. Additionally, the g-C3N4 NSs reversed the Cd-induced chlorosis, increased photosynthetic efficiency because of enhancement in Fv/Fm ration, Y(II) and sugars content. These results provide new insights into the alleviation of Cd toxicity to plants by g-C3N4 NSs, and shed light on the application of low-cost and environmental-friendly carbon-based NMs for alleviating heavy metal toxicity to plants.

Mechanisms of cadmium mitigation in tomato plants under orthophosphate and polyphosphate fertilization regimes

Cadmium (Cd) is one of the most toxic elements in soil, affecting morphological, physiological, and biochemical processes in plants. Mineral plant nutrition was tested as an effective approach to mitigate Cd stress in several crop species. In this regard, the present study aimed to elucidate how different phosphorus (P) fertilization regimes can improve some bio-physiological processes in tomato plants exposed to Cd stress. In a hydroponic experiment, the impact of two phosphorus fertilizer forms (Polyphosphate (poly-P): condensed P-form with 100% polymerization rate and orthophosphate (ortho-P): from orthophosphoric acid) on the photosynthetic activity, plant growth, and nutrient uptake was assessed under three levels of Cd stress (0, 12, and 25 µM of CdCl2). The obtained results confirmed the negative effects of Cd stress on the chlorophyll content and the efficiency of the photosynthesis machinery. The application of poly-P fertilizer significantly improved the chlorophyll stability index (82%) under medium Cd stress (Cd12), as compared to the ortho-P form (55%). The analysis of the chlorophyll α fluorescence transient curve revealed that the amplitude of Cd effect on the different steps of electron transfer between PSII and PSI was significantly reduced under the poly-P fertilization regime compared to ortho-P, especially under Cd12. The evaluation of the RE0/RC parameter showed that the electron flux reducing end electron acceptors at the PSI acceptor side per reaction center was significantly improved in the poly-P treatment by 42% under Cd12 compared to the ortho-P treatment. Moreover, the use of poly-P fertilizer enhanced iron uptake and its stoichiometric homeostasis in the shoot tissue which maintained an adequate absorption of iron under Cd stress conditions. Findings from this study revealed for the first time that inorganic polyphosphate fertilizers can reduce Cd toxicity in tomato plants by enhancing photosynthesis activity, nutrient uptake, plant growth, and biomass accumulation despite the high level of cadmium accumulation in shoot tissues.

Co-inoculation of rhizobia and AMF improves growth, nutrient uptake, and cadmium resistance of black locust grown in sand culture

Rhizobia and arbuscular mycorrhizal fungi (AMF) are symbiotic microorganisms important for plants grown in nutrient-deficient and heavy metal-contaminated soils. However, it remains unclear how plants respond to the coupled stress by heavy metal and nitrogen (N) deficiency under co-inoculation. Here, we investigated the synergistic effect of Mesorhizobium huakuii QD9 and Funneliformis mosseae on the response of black locust (Robinia pseudoacacia L.) grown in sand culture to cadmium (Cd) under N deficiency conditions. The results showed that single inoculation of AMF improved the growth and Cd resistance of black locust, co-inoculation improved the most. Compared to non-inoculated controls, co-inoculation mediated higher biomass and antioxidant enzyme activity, reduced oxidative stress, and promoted nodulation, mycorrhizal colonization, photosynthetic capacity, and N, P, Fe and Mg acquisition when exposed to Cd. This increase was significantly higher under N deficiency compared to N sufficiency. In addition, the uptake of Cd by co-inoculated black locust roots increased, but Cd translocation to the above-ground decreased under both N deficiency and sufficiency. Thus, in the tripartite symbiotic system, not merely metabolic processes but also Cd uptake increased under N deficiency. However, enhanced Cd detoxification in the roots and reduced allocation to the shoot likely prevent Cd toxicity and rather stimulated growth under these conditions.

Modulation of plant photosynthetic processes during metal and metalloid stress, and strategies for manipulating photosynthesis-related traits

Metals constitute vital elements for plant metabolism and survival, acting as essential co-factors in cellular processes which are indispensable for plant growth and survival. Excess or deficient provision of metal/metalloids puts plant's life and survival at risk, thus considered a potent stress for plants. Chloroplasts as an organelle with a high metal demand form a pivotal site within the metal homeostasis network. Therefore, the metal-mediated electron transport chain (ETC) in chloroplasts is a primary target site of metal/metalloid-induced stresses. Both excess and deficient availability of metal/metalloids threatens plant's photosynthesis in several ways. Energy demands from the photosynthetic carbon reactions should be in balance with energy output of ETC. Malfunctioning of ETC components as a result of metal/metalloid stress initiates photoinhiition. A feedback inhibition from carbon fixation process also impedes the ETC. Metal stress impairs antioxidant enzyme activity, pigment biosynthesis, and stomatal function. However, genetic manipulations, nutrient management, keeping photostasis, and application of phytohormones are among strategies for coping with metal stress. Consequently, a comprehensive understanding of the underlying mechanisms of metal/metalloid stress, as well as the exploration of potential strategies to mitigate its impact on plants are imperative. This review offers a mechanistic insight into the disruption of photosynthesis regulation by metal/metalloids and highlights adaptive approaches to ameliorate their effects on plants. Focus was made on photostasis, nutrient interactions, phytohormones, and genetic interventions for mitigating metal/metalloid stresses.

Methyl jasmonate reduces cadmium toxicity by enhancing phenol and flavonoid metabolism and activating the antioxidant defense system in pigeon pea (Cajanus cajan)

Cadmium (Cd) is absorbed by plant roots from soil along with essential nutrients and affects plant growth and productivity. Methyl jasmonate (Me-JA) play important roles to mitigate Cd toxicity in plants. We have investigated the role of Me-JA to ameliorate Cd toxicity in Pigeon pea (Cajanus cajan). Plant root growth, biomass, cellular antioxidant defense system and expression of key regulatory genes in molecular and signaling process have been analyzed. Two Cajanus cajan varieties AL-882 and PAU-881 were grown at 25 °C, 16/8h light/dark conditions in three biological replicates at 5 mM Cd concentration, three concentration of Me-JA (0, 10 nM, 100 nM) and two concentrations in combination of Me-JA + Cd (10 nM Me-JA +5 mM Cd, 100 nM Me-JA +5 mM Cd). The seedlings were exposed to Cd stress consequently plants showed decrease in primary root growth (60.71%, in AL-882 and 8.33%, in PAU-881), shoot and root biomass and antioxidant enzymes activities. Me-JA treatment resulted in increased primary root growth (63.64%, in AL-882) and overall plant biomass. Oxidative stress generated due to Cd stress was counter balanced by Me-JA treatment. Me-JA reduced H2O2 free radicals formation and enhanced antioxidant enzyme activities and phenolic content in stressed seedlings. Me-JA treatment increased expression of CALM, IP3, CDPK2, MPKs (involved in calcium and kinase signaling pathways) and reduced expression of metal transporters (IRT1 and HMA3) genes. This reduction in metal transporters gene expression is a probable reason for low toxicity effect of Cd in root after Me-JA treatment which has potential implications in reducing the risk of Cd in the food chain.

Phytotoxic effects of polyethylene microplastics combined with cadmium on the photosynthetic performance of maize (Zea mays L.)

Microplastics (MPs) and cadmium (Cd) has attracted increasing attention due to their combined toxicity to terrestrial vegetation. Photosynthesis which utilizes light energy to synthesize organic substances is crucial for crop production. However, the plant photosynthetic response to the joint toxicity of MPs and Cd is still unknown. Here, we studied the effects of polyethylene (PE) MPs on the photosynthetic performance of two maize cultivars Xianyu 335 (XY) and Zhengdan 958 (ZD) grown in a Cd contaminated soil. Results showed that the leaf Cd concentration in XY and ZD reached 26.1 and 31.9 μg g-1, respectively. PE-MPs did not influence the leaf Cd content, but posed direct and negative effects on photosynthesis by increasing the malondialdehyde content, reducing the chlorophyll content, inhibiting photosynthetic capacity, disrupting the PSII donor side, blocking electron transfer in different photosystems, and suppressing the oxidation and reduction states of PSI. Transcriptomic analysis revealed that the inhibitory effect of combined PE-MPs and Cd on maize photosynthesis was attributed to suppressed expression of the genes encoding PSII, PSI, F-type ATPase, cytochrome b6/f complex, and electron transport between PSII and PSI. Using WGCNA, we identified a MEturquoise module highly correlated with photosynthetic traits. Hub genes bridging carbohydrate metabolism, amino acid metabolism, lipid metabolism, and translation provided the molecular mechanisms of PE-MPs and Cd tolerance in maize plants. The comprehensive information on the phytotoxicity mechanisms of Cd stress in the presence or absence of PE-MPs on the photosynthesis of maize is helpful for cloning Cd and PE-MP resistance genes in the future.

Blue Light Enhances Cadmium Tolerance of the Aquatic Macrophyte Potamogeton crispus

Cadmium (Cd) is highly toxic and widely distributed in aquatic systems due to its high solubility and mobility in water, which can severely inhibit the survival of aquatic macrophytes. The phytotoxicity of Cd depends on environmental factors; however, it remains unclear whether and how light quality affects its toxicity on aquatic macrophytes. In this study, we investigated the effects of Cd on aquatic macrophytes Potamogeton crispus under different light qualities (white, blue, and red light). We evaluated morphological and photo-physiological traits, as well as the cellular antioxidant defense system. Our findings indicate that P. crispus under Cd stress showed notable damage in leaf morphology, decreased photosynthetic efficiency, inhibited HCO₃^- uptake, and reduced antioxidant enzyme activities, as well as oxidative damage indicated by MDA accumulation and superoxide (O₂^-) overproduction. However, compared with white or red light under Cd stress, blue light reduced structural damage and oxidative stress caused by Cd while increasing pigment synthesis and photosynthetic efficiency, as well as increasing ascorbate peroxidase (APX) activity. In conclusion, the changes induced by blue light in P. crispus's photosynthesis and antioxidant system strengthen its tolerance to Cd. Further research on signal transmission in relation to light quality in Cd-exposed aquatic plants is still needed.

Drought-free future climate conditions enhance cadmium phytoremediation capacity by Brassica napus through improved physiological status

This study aimed to assess Cd phytoextraction efficiency in well-watered and drought-stressed B. napus plants under current climate (CC, 21/14 °C, 400 ppm CO₂) and future climate (FC, 25/18 °C, 800 ppm CO₂) conditions. The underlying physiological mechanisms underpinning the obtained results were investigated by studying Cd (1, 10, 50, and 100 mg kg^-1) effect on B. napus photosynthetic performance and nutritional status. Only the Cd-50 and Cd-100 treatments caused visible leaf lesions, growth retardation, reductions in both gas exchange and chlorophyll fluorescence-related parameters, and disturbed mineral nutrient balance. Under CC conditions, well-watered plants were affected more than under FC conditions. The most important pathway by which Cd affected B. napus photosynthetic efficiency in well-watered plants was the damage to both photosystems, lowering photosynthetic electron transport. Meanwhile, non-stomatal and stomatal limitations were responsible for the higher reduction in the photosynthetic rate (P_r) of drought-stressed compared to well-watered plants. The significantly higher shoot dry weight, which had a strong positive relationship with P_r, was the main factor determining significantly higher shoot Cd accumulation in high Cd treatments in well-watered plants under FC conditions, resulting in a 65% (p < 0.05) higher soil Cd removal rate in the Cd-50 treatment.

Graphene-Cu Nanocomposites Induce Tolerance against Fusarium oxysporum, Increase Antioxidant Activity, and Decrease Stress in Tomato Plants

The tomato crop is susceptible to various types of stress, both biotic and abiotic, which affect the morphology, physiology, biochemistry, and genetic regulation of plants. Among the biotic factors, is the phytopathogen Fusarium oxysporum f. sp. lycopersici (Fol), which can cause losses of up to 100%. Graphene-Cu nanocomposites have emerged as a potential alternative for pathogen control, thanks to their antimicrobial activity and their ability to induce the activation of the antioxidant defense system in plants. In the present study, the effect of the Graphene-Cu nanocomposites and the functionalization of graphene in the tomato crop inoculated with Fol was evaluated, analyzing their impacts on the antioxidant defense system, the foliar water potential (Ψ_h), and the efficiency of photosystem II (PSII). The results demonstrated multiple positive effects; in particular, the Graphene-Cu nanocomposite managed to delay the incidence of the "vascular wilt" disease and reduce the severity by 29.0%. This translated into an increase in the content of photosynthetic pigments and an increase in fruit production compared with Fol. In addition, the antioxidant system of the plants was improved, increasing the content of glutathione, flavonoids, and anthocyanins, and the activity of the GPX, PAL, and CAT enzymes. Regarding the impact on the water potential and the efficiency of the PSII, the plants inoculated with Fol and treated with the Graphene-Cu nanocomposite responded better to biotic stress compared with Fol, reducing water potential by up to 31.7% and Fv/Fm levels by 32.0%.

Hormesis Responses of Photosystem II in Arabidopsis thaliana under Water Deficit Stress

Since drought stress is one of the key risks for the future of agriculture, exploring the molecular mechanisms of photosynthetic responses to water deficit stress is, therefore, fundamental. By using chlorophyll fluorescence imaging analysis, we evaluated the responses of photosystem II (PSII) photochemistry in young and mature leaves of Arabidopsis thaliana Col-0 (cv Columbia-0) at the onset of water deficit stress (OnWDS) and under mild water deficit stress (MiWDS) and moderate water deficit stress (MoWDS). Moreover, we tried to illuminate the underlying mechanisms in the differential response of PSII in young and mature leaves to water deficit stress in the model plant A. thaliana. Water deficit stress induced a hormetic dose response of PSII function in both leaf types. A U-shaped biphasic response curve of the effective quantum yield of PSII photochemistry (Φ_PSII) in A. thaliana young and mature leaves was observed, with an inhibition at MiWDS that was followed by an increase in Φ_PSII at MoWDS. Young leaves exhibited lower oxidative stress, evaluated by malondialdehyde (MDA), and higher levels of anthocyanin content compared to mature leaves under both MiWDS (+16%) and MoWDS (+20%). The higher Φ_PSII of young leaves resulted in a decreased quantum yield of non-regulated energy loss in PSII (Φ_NO), under both MiWDS (-13%) and MoWDS (-19%), compared to mature leaves. Since Φ_NO represents singlet-excited oxygen (¹O₂) generation, this decrease resulted in lower excess excitation energy at PSII, in young leaves under both MiWDS (-10%) and MoWDS (-23%), compared to mature leaves. The hormetic response of PSII function in both young and mature leaves is suggested to be triggered, under MiWDS, by the intensified reactive oxygen species (ROS) generation, which is considered to be beneficial for activating stress defense responses. This stress defense response that was induced at MiWDS triggered an acclimation response in A. thaliana young leaves and provided tolerance to PSII when water deficit stress became more severe (MoWDS). We concluded that the hormesis responses of PSII in A. thaliana under water deficit stress are regulated by the leaf developmental stage that modulates anthocyanin accumulation in a stress-dependent dose.

Toxic effects of cadmium on the physiological and biochemical attributes of plants, and phytoremediation strategies: A review

Anthropogenic activities pose a more significant threat to the environment than natural phenomena by contaminating the environment with heavy metals. Cadmium (Cd), a highly poisonous heavy metal, has a protracted biological half-life and threatens food safety. Plant roots absorb Cd due to its high bioavailability through apoplastic and symplastic pathways and translocate it to shoots through the xylem with the help of transporters and then to the edible parts via the phloem. The uptake and accumulation of Cd in plants pose deleterious effects on plant physiological and biochemical processes, which alter the morphology of vegetative and reproductive parts. In vegetative parts, Cd stunts root and shoot growth, photosynthetic activities, stomatal conductance, and overall plant biomass. Plants' male reproductive parts are more prone to Cd toxicity than female reproductive parts, ultimately affecting their grain/fruit production and survival. To alleviate/avoid/tolerate Cd toxicity, plants activate several defense mechanisms, including enzymatic and non-enzymatic antioxidants, Cd-tolerant gene up-regulations, and phytohormonal secretion. Additionally, plants tolerate Cd through chelating and sequestering as part of the intracellular defensive mechanism with the help of phytochelatins and metallothionein proteins, which help mitigate the harmful effects of Cd. The knowledge on the impact of Cd on plant vegetative and reproductive parts and the plants' physiological and biochemical responses can help selection of the most effective Cd-mitigating/avoiding/tolerating strategy to manage Cd toxicity in plants.

Sensitivity of the Photosynthetic Apparatus in Maize and Sorghum under Different Drought Levels

Drought is one of the main environmental stress factors affecting plant growth and yield. The impact of different PEG concentrations on the photosynthetic performance of maize (Zea mays L. Mayflower) and sorghum (Sorghum bicolor L. Foehn) was investigated. The activity of the photosynthetic apparatus was assessed using chlorophyll fluorescence (PAM and JIP test) and photooxidation of P₇₀₀. The data revealed that water deficiency decreased the photochemical quenching (qP), the ratio of photochemical to nonphotochemical processes (Fv/Fo), the effective quantum yield of the photochemical energy conversion in PSII (Φ_PSII), the rate of the electron transport (ETR), and the performance indexes PI_total and PI_ABS, as the impact was stronger in sorghum than in maize and depended on drought level. The PSI photochemistry (P₇₀₀ photooxidation) in sorghum was inhibited after the application of all studied drought levels, while in maize, it was registered only after treatment with higher PEG concentrations (30% and 40%). Enhanced regulated energy losses (Φ_NPQ) and activation of the state transition under drought were also observed in maize, while in sorghum, an increase mainly in nonregulated energy losses (Φ_NO). A decrease in pigment content and relative water content and an increase in membrane damage were also registered after PEG treatment. The experimental results showed better drought tolerance of maize than sorghum. This study provides new information about the role of regulated energy losses and state transition for the protection of the photosynthetic apparatus under drought and might be a practical approach to the determination of the drought tolerance of plants.

Common weeds as heavy metal bioindicators: a new approach in biomonitoring

Environmental pollution by heavy metals affects both urban and non-urban areas of Europe and the world. The use of bioindicator plants for the detection of these pollutants is a common practice. An important property of potential bioindicators is their easy availability and wide distribution range, which means that they can be practically used over a wide area. Therefore, common and widely distributed weeds: Trifolium pratense L., Rumex acetosa L., Amaranthus retroflexus L., Plantago lanceolata L., ornamental species Alcea rosea L., and Lolium multiflorum L. var. Ponto were selected as a potential bioindicators of heavy metals (Cd, Pb, Cu, Zn). Plants were exposed in the same soil conditions in three sample sites in the Poznań city. It was found that all species had heavy metal accumulation potential, especially A. rosea, P. lanceolata and L. multiflorum for Zn (BCF = 6.62; 5.17; 4.70) and A. rosea, P. lanceolata for Cd (BCF = 8.51; 6.94). Translocation of Cu and Zn was the most effective in T. pratense (TF_Cu = 2.55; TF_Zn = 2.67) and in A. retroflexus (TF_Cu = 1.50; TF_Zn = 2.23). Cd translocation was the most efficient in T. pratense (TF_Cd = 1.97), but PB was the most effective translocated in A. retroflexus (TF_Pb = 3.09).. Based on physiological response to stress, it was detected an increasing level of hydrogen peroxide (H₂O₂) in roots and leaves of all samples, with the highest in all organs of A. rosea. Enzymatic activity levels of CAT, APOX, and also the marker of polyunsaturated fatty acid peroxidation MDA, were higher after 6 weeks of exposure in comparison to control samples and varied in time of exposure and between species and exposure. After the experiment, in almost all samples we detected a reduction of chlorophyll content and relative water content, but in efficiency of photosynthesis parameters: net photosynthesis rate, intercellular CO₂ concentration and stomatal conductance, we noted increased values, which proved the relatively good condition of the plants. The examined weeds are good bioindicators of heavy metal contamination, and their combined use makes it possible to comprehensively detection of environmental threats.

Cadmium accumulation by Phragmites australis and Iris pseudacorus from stormwater in floating treatment wetlands microcosms: Insights into plant tolerance and utility for phytoremediation

Environmentally sustainable remediation is needed to protect freshwater resources which are deteriorating due to severe industrial, mining, and agricultural activities. Treatment by floating wetlands could be a sustainable solution to remediate water bodies. The study aimed to examine the effects of Cd on Phragmites australis and Iris pseudacorus growth (height, biomass, root length and chlorophyll contents), anatomy, Cd accumulation in their biomass and their ability to remove Cd, N and P. Seedlings of both plants were grown in a greenhouse for 50 days in artificially prepared stormwater amended with Cd, N, and P. The treatments were: control (Cd _0), Cd_1, Cd_2, and Cd_4 mg L^-1. N and P contents were 4 mg L^-1 and 1.8 mg L^-1, respectively. In the case of P. australis, the maximum plant height, root length, and total dry biomass production was increased in medium dose (Cd_2) treatment while the chlorophyll index (CCI) increased in high dose (Cd_4) treatment as compared to all treatments. For I. pseudacorus, the maximum plant height and total dry biomass production, root length and CCI values were improved in low dose (Cd_1) and high dose (Cd_4) treatments, respectively among all treatments. Results showed that P. australis accumulated 10.94-1821.59 μg · (0.05 m²)^-1 in roots and 2.45-334.65 μg · (0.05 m²)^-1 in shoots under Cd_0, Cd_1 and Cd_4 treatments. I. pseudacorus accumulated the highest Cd in roots up to 5.84-4900 μg · (0.05 m²)^-1 and 3.40-609 μg · (0.05 m²)^-1 in shoots under Cd_0, Cd_1 and Cd_4 treatments. The translocation factor was observed as <1 and the bioconcentration factor >1 for both species, which indicates their phytostabilization potential. Results demonstrate that P. australis and I. pseudacorus are suitable for use in floating wetlands to remediate contaminated sites.

Phytotoxic effects of chemically synthesized copper oxide nanoparticles induce physiological, biochemical, and ultrastructural changes in Cucumis melo

Nanotechnology has achieved great attention due to its impressive performance especially engineered nanoparticles (ENPs). Copper-based nanoparticles offer favorable development in the fabrication of agrochemicals including fertilizers and pesticides in the field of agriculture. However, their toxic impact on melon plants (Cucumis melo) still needs to be investigated. Therefore, the aim of the current work was performed to focus on the toxic impact of Cu oxide nanoparticles (CuONPs) in hydroponically grown Cucumis melo. Our results demonstrated that CuONPs with 75, 150, and 225 mg/L significantly (P<0.005) suppressed the growth rate and badly affect physiological and biochemical activities in melon seedlings. Also, results revealed remarkable phenotypical changes besides significantly reduced fresh biomass and decreased levels of total chlorophyll contents in a dose-dependent manner. Atomic absorption spectroscopy (ASS) analysis exhibited that C. melo treated with CuONPs accumulates NPs in the shoot. Moreover, exposure to higher CuONPs (75-225mg/L) significantly increased the reactive oxygen species (ROS) accumulation, malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) level in the shoot and induced toxicity in melon root with an increase in electrolyte leakage. Furthermore, antioxidant enzyme peroxidase (POD) and superoxide dismutase (SOD) activity in the shoot significantly increased under exposure to higher CuONPs. Exposure to higher concentrations of CuONPs (225 mg/L) significantly deformed the stomatal aperture. Furthermore, reducing the number and abnormal size of palisade mesophyll and spongy mesophyll cells were investigated especially at high doses of CuONPs. Overall, our current work demonstrates that CuONPs of 10-40 nm size provide direct evidence for a toxic effect in C. melo seedlings. Our findings were expected to inspire the safe production of NPs and agrifood security. Thus, CuONPs prepared from toxic route and its bioaccumulation into our food chain through crop plants possess a serious threat to the ecological system.

Phytohormones enhance heavy metal responses in Euglena gracilis: Evidence from uptake of Ni, Pb and Cd and linkages to hormonomic and metabolomic dynamics

Over the last decade, significant effort has been made to understand phytohormonal functions (e.g., cytokinins (CKs) and abscisic acid (ABA)) in metal stress responses of higher plants and algae. Despite the potential for these phytohormones to improve industrial remediation by Euglena gracilis (Euglenophyceae), no such roles have been elucidated for this highly adaptive species and its response to heavy metals. This study demonstrates that toxic metals (nickel, lead, cadmium) modify hormonal activity profiles (i.e., CK forms and their concentrations) in E. gracilis. Furthermore, exogenous ABA or CK (tZ) enabled higher metal uptake efficiency (i.e., 9.35% in lead and 9.2% in cadmium uptake with CK) and alleviated metal toxicity through the regulation of endogenous CKs (i.e., total CK, isoprenoid CK) and gibberellin (GAs, GA₁ and GA₃) levels. These responses suggest that E. gracilis regulates multiple phytohormone signals during metal stress acclimation. A deeper approach, using untargeted metabolomic analyses, gave more detailed insight into phytohormone-controlled pathways and associated modified metabolites, which were frequently related to metal accumulation and the physiological acclimation to metal presence. Significant changes in the levels of cellular metabolites, especially those involved in acclimation to metal stress, were under the influence of phytohormones in algal cells. When grown under metal stress conditions, the presence of exogenous ABA or CKs, caused changes in cellular metabolites which included those from: lipid pathways, riboflavin metabolism, the biosynthesis of cofactors/vitamins, and carbohydrate metabolism. Also, bioactive secondary metabolites (e.g., terpenoids, alkaloids, flavonoids, carotenoids) were modified in algal cells treated with phytohormones. Thus, the study gives a detailed view on the regulatory functions of ABA and CKs in algal metal bioremediation strategies, which are attributed to enhanced metal uptake and in the fine-tuning of plant hormone levels during metal stress response. The results can guide efforts to develop efficient, low-cost and environmentally friendly methods for bioremediation.

Overexpression of RtSYP121 confers cadmium colerance by promoting vesicle trafficking, maintaining ion homeostasis, and alleviating photosynthetic inhibition in Arabidopsis

Cadmium (Cd) is a toxic heavy metal in soil that seriously threatens crop production, food security, and human health. Syntaxins, a prototype family of Soluble N-ethyl-maleimide-associated protein receptors (SNAREs) involved in vesicle trafficking, are implicated in resistance to abiotic stresses, including Cd stress, but the molecular mechanisms underlying the involvement of syntaxins in Cd tolerance in plants are unclear. In this study, we isolated and functionally characterized the syntaxin gene RtSYP121 from Reaumuria trigyna to evaluate its potential for phytoremediation. RtSYP121 resides in the plasma membrane. The transcriptional level of RtSYP121 was strongly increased by salt, drought, and Cd stress. Overexpression of RtSYP121 significantly enhanced the Cd tolerance of transgenic Arabidopsis. The Cd tolerance of transgenic plants mainly depended on elevated vesicle trafficking, which increased the content of K⁺ and Ca²⁺ and thus decreased the accumulation of Cd²⁺ by regulating the delivery or activity of ion transporters, channels, and pumps. Moreover, overexpression of RtSYP121 in Arabidopsis ameliorated Cd stress-induced phytotoxic effects, including growth inhibition, ROS burst, photosynthetic impairment, and cell death. Therefore, we suggest that RtSYP121 plays multiple roles in the plant response to Cd stress by promoting vesicle trafficking, maintaining ion homeostasis, and alleviating photosynthetic inhibition.

Lignin-Loaded Carbon Nanoparticles as a Promising Control Agent against Fusarium verticillioides in Maize: Physiological and Biochemical Analyses

Lignin, a naturally occurring biopolymer, is produced primarily as a waste product by the pulp and paper industries and burned to produce electricity. Lignin-based nano- and microcarriers found in plants are promising biodegradable drug delivery platforms. Here, we highlight a few characteristics of a potential antifungal nanocomposite consisting of carbon nanoparticles (C-NPs) with a defined size and shape containing lignin nanoparticles (L-NPs). Spectroscopic and microscopic studies verified that the lignin-loaded carbon nanoparticles (L-CNPs) were successfully prepared. Under in vitro and in vivo conditions, the antifungal activity of L-CNPs at various doses was effectively tested against a wild strain of F. verticillioides that causes maize stalk rot disease. In comparison to the commercial fungicide, Ridomil Gold SL (2%), L-CNPs introduced beneficial effects in the earliest stages of maize development (seed germination and radicle length). Additionally, L-CNP treatments promoted positive effects on maize seedlings, with a significant increment in the level of carotenoid, anthocyanin, and chlorophyll pigments for particular treatments. Finally, the soluble protein content displayed a favorable trend in response to particular dosages. Most importantly, treatments with L-CNPs at 100 and 500 mg/L significantly reduced stalk rot disease by 86% and 81%, respectively, compared to treatments with the chemical fungicide, which reduced the disease by 79%. These consequences are substantial considering the essential cellular function carried out by these special natural-based compounds. Finally, the intravenous L-CNPs treatments in both male and female mice that affected the clinical applications and toxicological assessments are explained. The results of this study suggest that L-CNPs are of high interest as biodegradable delivery vehicles and can be used to stimulate favorable biological responses in maize when administered in the recommended dosages, contributing to the idea of agro-nanotechnology by demonstrating their unique qualities as a cost-effective alternative compared to conventional commercial fungicides and environmentally benign nanopesticides for long-term plant protection.

Hormesis Responses of Growth and Photosynthetic Characteristics in Lonicera japonica Thunb. to Cadmium Stress: Whether Electric Field Can Improve or Not?

"Hormesis" is considered a dose-response phenomenon mainly observed at hyperaccumulator plants under heavy metals stress. In this study, the effects of electric fields on hormesis responses in Lonicera japonica Thunb. under cadmium (Cd) treatments were investigated by assessing the plant growth and photosynthetic characteristics. Under Cd treatments without electric fields, the parameters of plant growth and photosynthetic characteristics increased significantly when exposed to 5 mg L^-1 Cd, and decreased slightly when exposed to 25 mg L^-1 Cd, showing an inverted U-shaped trend, which confirmed that low concentration Cd has a hormesis effect on L. japonica. Under electric fields, different voltages significantly promoted the inverted U-shaped trend of the hormesis effect on the plant, especially by 2 V cm^-1 voltage. Under 2 V cm^-1 voltage, the dry weight of the root and leaf biomass exposed to 5 mg L^-1 Cd increased significantly by 38.38% and 42.14%, and the photosynthetic pigment contents and photosynthetic parameters were also increased significantly relative to the control, indicating that a suitable electric field provides better improvements for the hormesis responses of the plant under Cd treatments. The synergistic benefits of the 5 mg L^-1 Cd and 2 V cm^-1 electric field in terms of the enhanced hormesis responses of growth and photosynthetic characteristics could contribute to the promoted application of electro-phytotechnology.

Antifungal activity of eco-safe nanoemulsions based on Nigella sativa oil against Penicillium verrucosum infecting maize seeds: Biochemical and physiological traits

The main goals of the present investigation were to develop O/W nanoemulsion fungicides based on cold-pressed Nigella sativa (black seed) oil to prevent Penicillium verrucosum infection of maize seeds and to test their antifungal activity against this fungus. Additionally, the effect of these nanoemulsions on plant physiological parameters was also investigated. Two nonionic surfactants namely Tween 20 and Tween 80 were used as emulsifying agents in these formulations. The effect of sonication time and surfactant type on the mean droplet size, polydispersity index (PDI), and zeta potential of the nanoemulsions were determined by dynamic light scattering (DLS). Results indicated that both sonication time and emulsifier type had pronounced effects on the stability of O/W nanoemulsions with a small particle size range (168.6-345.3 nm), acceptable PDI (0.181-0.353), and high zeta potential (-27.24 to -48.82 mV). Tween 20 showed superior stability compared to Tween 80 nanoemulsions. The in vitro results showed that complete inhibition of P. verrucosum-growth was obtained by 10_T80 and 10_T20 nanoemulsions at 100% concentration. All nanoemulsions had increment effects on maize seed germination by 101% in the case of 10_T20 and 10_T80 compared to untreated seeds or the chemical fungicide treatment. Nanoemulsions (10_T20 and 10_T80) were able to stimulate root and shoot length as compared to the fungicide treatment. Seed treatment with 10_T80 nanoemulsion showed the highest AI and protease activity by 75 and 70%, respectively, as compared to the infected control. The produced nanoemulsions might provide an effective protectant coating layer for the stored maize seeds.

Cadmium toxicity in medicinal plants: An overview of the tolerance strategies, biotechnological and omics approaches to alleviate metal stress

Medicinal plants, an important source of herbal medicine, are gaining more demand with the growing human needs in recent times. However, these medicinal plants have been recognized as one of the possible sources of heavy metal toxicity in humans as these medicinal plants are exposed to cadmium-rich soil and water because of extensive industrial and agricultural operations. Cadmium (Cd) is an extremely hazardous metal that has a deleterious impact on plant development and productivity. These plants uptake Cd by symplastic, apoplastic, or via specialized transporters such as HMA, MTPs, NRAMP, ZIP, and ZRT-IRT-like proteins. Cd exerts its effect by producing reactive oxygen species (ROS) and interfere with a range of metabolic and physiological pathways. Studies have shown that it has detrimental effects on various plant growth stages like germination, vegetative and reproductive stages by analyzing the anatomical, morphological and biochemical changes (changes in photosynthetic machinery and membrane permeability). Also, plants respond to Cd toxicity by using various enzymatic and non-enzymatic antioxidant systems. Furthermore, the ROS generated due to the heavy metal stress alters the genes that are actively involved in signal transduction. Thus, the biosynthetic pathway of the important secondary metabolite is altered thereby affecting the synthesis of secondary metabolites either by enhancing or suppressing the metabolite production. The present review discusses the abundance of Cd and its incorporation, accumulation and translocation by plants, phytotoxic implications, and morphological, physiological, biochemical and molecular responses of medicinal plants to Cd toxicity. It explains the Cd detoxification mechanisms exhibited by the medicinal plants and further discusses the omics and biotechnological strategies such as genetic engineering and gene editing CRISPR- Cas 9 approach to ameliorate the Cd stress.

Effect of exogenous melatonin on improvement of chlorophyll content and photochemical efficiency of PSII in mallow plants (Malva parviflora L.) treated with cadmium

Melatonin is a growth regulator that improves the growth and chlorophyll (chl) content in plants. This study aims to investigate the effect of melatonin pretreatment on chl synthesis and fluorescence parameters in Malva parviflora exposed to cadmium (Cd). The 42-day-old plants were transferred to nutrient solutions containing 50 μM melatonin. After two days, some plants were exposed to 50 μM Cd. Eight days after Cd treatment, some indicators related to chl fluorescence and some biochemical parameters were measured. In this study, melatonin increased chl content and chl a/pheophytin a (pheo a) ratio, chlorophyllide a (chlide a), porphyrin compounds, and 5-aminolevulinic acid (5-ALA) in the presence of Cd. However, it decreased chl a/chlide a ratio under these conditions. Whereas Cd treatment resulted in significant reductions in photochemical activity and electron transfer rate in PSII, melatonin improved photochemical efficiency of PSII by reducing the toxic effect of Cd on the activity of the oxygen evolving complex (OEC) on the electron donor site and reducing non-photochemical quenching (NPQ). Based on the results, it appears that melatonin can maintain the chl content of plants exposed to Cd by increasing the precursors of the chl biosynthesis pathway and reducing its degradation rate. These results may, at least in our experimental conditions, partly explain the reason for the improved yield and growth of Cd-exposed plants when pretreated with melatonin.

UVB-Pretreatment-Enhanced Cadmium Absorption and Enrichment in Poplar Plants

The phenomenon of cross adaptation refers to the ability of plants to improve their resistance to other stress after experiencing one type of stress. However, there are limited reports on how ultraviolet radiation B (UVB) pretreatment affects the enrichment, transport, and tolerance of cadmium (Cd) in plants. Since an appropriate UVB pretreatment has been reported to change plant tolerance to stress, we hypothesized that this application could alter plant uptake and tolerance to heavy metals. In this study, a woody plant species, 84K poplar (Populus alba × Populus glandulosa), was pretreated with UVB and then subjected to Cd treatment. The RT-qPCR results indicated that the UVB-treated plants could affect the expression of Cd uptake, transport, and detoxification-related genes in plants, and that the UVB-Pretreatment induced the ability of Cd absorption in plants, which significantly enriched Cd accumulation in several plant organs, especially in the leaves and roots. The above results showed that the UVB-Pretreatment further increased the toxicity of Cd to plants in UVB-Cd group, which was shown as increased leaf malonaldehyde (MDA) and hydrogen peroxide (H₂O₂) content, as well as downregulated activities of antioxidant enzymes such as Superoxide Dismutase (SOD), Catalase (CAT), and Ascorbate peroxidase (APX). Therefore, poplar plants in the UVB-Cd group presented a decreased photosynthesis and leaf chlorosis. In summary, the UVB treatment improved the Cd accumulation ability of poplar plants, which could provide some guidance for the potential application of forest trees in the phytoremediation of heavy metals in the future.

Physiological and biochemical bases of spermidine-induced alleviation of cadmium and lead combined stress in rice

Cadmium (Cd) and lead (Pb) pollution is a major environmental issue affecting plant production. Spermidine (Spd) is involved in plant response to abiotic stress. However, the role and associated mechanism of Spd under Cd + Pb combined stress are poorly understood. The potential protective role of Spd at different concentration on rice (Oryza sativa L.) seedlings exposed to Cd + Pb treatment was investigated by a hydroponic experiment in this study. The results showed that exogenous Spd enhanced the tolerance of rice seedlings to Cd + Pb stress, resulted in an increase in plant height, root length, fresh weight and dry weight of roots and shoots. Further, application of Spd decreased the contents of hydrogen peroxide, superoxide anion, malondialdehyde, and the accumulation of Cd and Pb, and increased the contents of mineral nutrient, carotenoids, chlorophyll, proline, soluble sugar, soluble protein, total phenol, flavonoid, anthocyanin, and antioxidant enzymes activities in roots and shoots of rice seedlings under Cd + Pb stress. Particularly, 0.5 mmol L^-1 Spd was the most effective to alleviate the adverse impacts on growth and physiological metabolism of rice seedlings under Cd + Pb stress. Principal component analysis and heat map clustering established correlations between physio-biochemical parameters and further revealed Spd alleviated Cd + Pb damage in rice seedling was associated with inhibition of accumulation and translocation of Cd and Pb, increasing the contents of photosynthetic pigments and mineral nutrient and stimulation of antioxidative response and osmotic adjustment. Overall, our findings provide an important prospect for use of Spd in modulating Cd + Pb tolerance in rice plants. Spd could help to alleviate Cd + Pb damage through inhibition of accumulation and translocation of Cd and Pb and stimulation of oxidant-defense system and osmotic adjustment.

The bioactivities of sclareol: A mini review

Sclareol, a diterpene alcohol isolated from the herbal and flavor plant clary sage (Salvia sclarea L.), is far-famed as the predominant ingredient in the refined oil of Salvia sclarea (L.). The empirical medicine of Salvia sclarea L. focused on various diseases, such as arthritis, oral inflammation, digestive system diseases, whereas the sclareol possessed more extensive and characteristic bioactivities, including anti-tumor, anti-inflammation and anti-pathogenic microbes, even anti-diabetes and hypertension. However, there is a deficiency of literature to integrate and illuminate the pharmacological attributes of sclareol based on well-documented investigations. Interestingly, sclareol has been recently considered as the potential candidate against COVID-19 and Parkinson’s disease. Accordingly, the bioactive attributes of sclareol in cancer, inflammation, even pharmacochemistry and delivery systems are reviewed for comprehensively dissecting its potential application in medicine.

A Hormetic Spatiotemporal Photosystem II Response Mechanism of Salvia to Excess Zinc Exposure

Exposure of Salvia sclarea plants to excess Zn for 8 days resulted in increased Ca, Fe, Mn, and Zn concentrations, but decreased Mg, in the aboveground tissues. The significant increase in the aboveground tissues of Mn, which is vital in the oxygen-evolving complex (OEC) of photosystem II (PSII), contributed to the higher efficiency of the OEC, and together with the increased Fe, which has a fundamental role as a component of the enzymes involved in the electron transport process, resulted in an increased electron transport rate (ETR). The decreased Mg content in the aboveground tissues contributed to decreased chlorophyll content that reduced excess absorption of sunlight and operated to improve PSII photochemistry (ΦPSII), decreasing excess energy at PSII and lowering the degree of photoinhibition, as judged from the increased maximum efficiency of PSII photochemistry (Fv/Fm). The molecular mechanism by which Zn-treated leaves displayed an improved PSII photochemistry was the increased fraction of open PSII reaction centers (qp) and, mainly, the increased efficiency of the reaction centers (Fv'/Fm') that enhanced ETR. Elemental bioimaging of Zn and Ca by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) revealed their co-localization in the mid-leaf veins. The high Zn concentration was located in the mid-leaf-vein area, while mesophyll cells accumulated small amounts of Zn, thus resembling a spatiotemporal heterogenous response and suggesting an adaptive strategy. These findings contribute to our understanding of how exposure to excess Zn triggered a hormetic response of PSII photochemistry. Exposure of aromatic and medicinal plants to excess Zn in hydroponics can be regarded as an economical approach to ameliorate the deficiency of Fe and Zn, which are essential micronutrients for human health.

Combined Impact of Excess Zinc and Cadmium on Elemental Uptake, Leaf Anatomy and Pigments, Antioxidant Capacity, and Function of Photosynthetic Apparatus in Clary Sage (Salvia sclarea L.)

Clary sage (Salvia sclarea L.) is a medicinal plant that has the potential to be used for phytoextraction of zinc (Zn) and cadmium (Cd) from contaminated soils by accumulating these metals in its tissues. Additionally, it has been found to be more tolerant to excess Zn than to Cd stress alone; however, the interactive effects of the combined treatment with Zn and Cd on this medicinal herb, and the protective strategies of Zn to alleviate Cd toxicity have not yet been established in detail. In this study, clary sage plants grown hydroponically were simultaneously exposed to Zn (900 µM) and Cd (100 μM) for 8 days to obtain more detailed information about the plant responses and the role of excess Zn in mitigating Cd toxicity symptoms. The leaf anatomy, photosynthetic pigments, total phenolic and anthocyanin contents, antioxidant capacity (by DPPH and FRAP analyses), and the uptake and distribution of essential elements were investigated. The results showed that co-exposure to Zn and Cd leads to an increased leaf content of Fe and Mg compared to the control, and to increased leaf Ca, Mn, and Cu contents compared to plants treated with Cd only. This is most likely involved in the defense mechanisms of excess Zn against Cd toxicity to protect the chlorophyll content and the functions of both photosystems and the oxygen-evolving complex. The data also revealed that the leaves of clary sage plants subjected to the combined treatment have an increased antioxidant capacity attributed to the higher content of polyphenolic compounds. Furthermore, light microscopy indicated more alterations in the leaf morphology after Cd-only treatment than after the combined treatment. The present study shows that excess Zn could mitigate Cd toxicity in clary sage plants.

Phosphate-solubilizing bacteria abate cadmium absorption and restore the rhizospheric bacterial community composition of grafted watermelon plants

The grafting of watermelon plants to rootstocks is common due to the strong capacity of rootstocks to adapt to abiotic and biotic stresses. However, the effect of phosphate-solubilizing bacteria (PSB) on grafted watermelon plant growth and bacterial structures in root soil is unclear. In this study, the growth and hormone levels of grafted plants were measured, and the bacterial communities under cadmium (Cd) stress and inoculation with PSB were sequenced in three treatments (S1, control; S2, 50 μmol Cd [CdCl₂]; and S3, 50 μmol Cd plus inoculation with the Cd-resistant PSB strain 'N3'). The results showed that inoculation with PSB significantly (P < 0.05) improved the total dry weight of the grafted plants. Typically, inoculation with PSB significantly (P < 0.05) reduced Cd content in scions and roots. The level of the phytohormone jasmonic acid increased in treatment S2, but decreased in treatment S3 under inoculation with PSB. The functional annotation of prokaryotic taxa showed that Cd decreased the abundance of nitrogen respiration and chloroplast functional groups. Nevertheless, inoculation with PSB helped restore bacterial community structures. These findings provide a new understanding of the effect of PSB on the promotion of seedling growth and bacterial communities in grafted watermelon plants under Cd stress.

Arbuscular mycorrhizal fungus regulates cadmium accumulation, migration, transport, and tolerance in Medicago sativa

Cadmium (Cd) pollution in croplands is a global environmental problem. Measures to improve the tolerance of sensitive crops and reduce pollutant absorption and accumulation are needed in contaminated agricultural areas, and inoculation with rhizosphere microorganisms to regulate plant resistance and heavy metal transport can provide an effective solution. A pot experiment was conducted to analyse the impact of arbuscular mycorrhizal fungi (AMF) on alfalfa oxidase activity, heavy metal resistance genes and transport proteins, metabolism, and other biochemical regulation mechanisms that lead to complexation, compartmentalisation, efflux, enrichment, and antioxidant detoxification pathways. The AMF reduced shoot and protoplasm Cd inflow, and promoted organic compound production (e.g., by upregulating HM-Res4 for 1.2 times), to complex with Cd, reducing its biological toxicity. The AMF increased the ROS scavenging efficiency and osmotic regulatory substance content of the alfalfa plants, reduced oxidative stress (ROS dereased), and maintained homeostasis. It also alleviated Cd inhibition of photosynthetic electron transport, tricarboxylic acid circulation, and nitrogen assimilation. These AMF effects improved leaf and root biomass by 43.87% and 59.71% and facilitated recovery of a conservative root economic strategy. It is speculated that AMF induces the resistance signal switch by regulating the negative feedback regulation mode of indole acetic acid upward transport and methyl jasmonate downward transmission in plants.

Cadmium Caused Different Toxicity to Photosystem I and Photosystem II of Freshwater Unicellular Algae Chlorella pyrenoidosa (Chlorophyta)

Heavy metals such as Cd pose environmental problems and threats to a variety of organisms. The effects of cadmium (Cd) on the growth and activities of photosystem I (PSI) and photosystem II (PSII) of Chlorella pyrenoidosa were studied. The growth rate of cells treated with 25 and 100 µM of Cd for longer than 48 h were significantly lower than the control, accompanying with the inhibition of photosynthesis. The result of quantum yields and electron transport rates (ETRs) in PSI and PSII showed that Cd had a more serious inhibition on PSII than on PSI. Cd decreased the efficiency of PSII to use the energy under high light with increasing Cd concentration. In contrast, the quantum yield of PSI did not show a significant difference among different Cd treatments. The activation of cyclic electron flow (CEF) and the inhibition of linear electron flow (LEF) due to Cd treatment were observed. The photochemical quantum yield of PSI and the tolerance of ETR of PSI to Cd treatments were due to the activation of CEF around PSI. The activation of CEF also played an important role in induction of non-photochemical quenching (NPQ). The binding features of Cd ions and photosystem particles showed that Cd was easier to combine with PSII than PSI, which may explain the different toxicity of Cd on PSII and PSI.

Synergetic modulation of plant cadmium tolerance via MYB75-mediated ROS homeostasis and transcriptional regulation

KEY MESSAGE

MYB75 enhances plant cadmium tolerance by mediating ROS homeostasis and cadmium tolerance-related genes expression. Cadmium (Cd) is a heavy metal with biological toxicity, which can be detoxified through chelation and compartmentation in plants. Transcriptional regulation mediates plant Cd tolerance by modulating these processes. However, the mechanism remains to be studied. Our results showed a previously unknown function of MYB75 transcription factor in the regulation of Cd tolerance. Cd exposure stimulates anthocyanin accumulation by raising MYB75 expression. Enhanced Cd tolerance was observed in the MYB75-overexpressing plants, whereas increased Cd sensitivity was found in the MYB75 loss-of-function mutants. Under Cd stress conditions, lower reactive oxygen species (ROS) levels were detected in MYB75-overexpressing plants than in wild type plants. In contrast, higher ROS levels were found in MYB75 loss-of-function mutants. Overexpression of MYB75 was associated with increased glutathione (GSH) and phytochelatin (PC) content under Cd exposure. Furthermore, the expression of Cd stress-related gene including ACBP2 and ABCC2 was elevated in MYB75-overexpressing plants, and this upregulation was mediated through the mechanism by which MYB75 directly bind to the promoter of ACBP2 and ABCC2. Our findings reveal an important role for MYB75 in the regulation of plant Cd tolerance via anthocyanin-mediated ROS homeostasis, and through upregulation of Cd stress-related gene at the transcriptional level.

Unraveling Cadmium Toxicity in Trifolium repens L. Seedling: Insight into Regulatory Mechanisms Using Comparative Transcriptomics Combined with Physiological Analyses

Trifolium repens (T. repens) can accumulate significant amounts of heavy metal ions, and has strong adaptability to wide environmental conditions, and relatively large biomass, which is considered a potential plant for phytoremediation. However, the molecular mechanisms of T. repens involved in Cd tolerance have not yet been studied in detail. This study was conducted to examine the integrative responses of T. repens exposed to a high-level CdCl₂ by investigating the physiological and transcriptomic analyses. The results suggested that T. repens seedlings had a high degree of tolerance to Cd treatment. The roots accumulated higher Cd concentration than leaves and were mainly distributed in the cell wall. The content of MDA, soluble protein, the relative electrolyte leakage, and three antioxidant enzymes (POD, SOD, and APX) was increased with the Cd treatment time increasing, but the CAT enzymes contents were decreased in roots. Furthermore, the transcriptome analysis demonstrated that the differentially expressed genes (DEGs) mainly enriched in the glutathione (GSH) metabolism pathway and the phenylpropanoid biosynthesis in the roots. Overexpressed genes in the lignin biosynthesis in the roots might improve Cd accumulation in cell walls. Moreover, the DEGs were also enriched in photosynthesis in the leaves, transferase activity, oxidoreductase activity, and ABA signal transduction, which might also play roles in reducing Cd toxicity in the plants. All the above, clearly suggest that T. repens employ several different mechanisms to protect itself against Cd stress, while the cell wall biosynthesis and GSH metabolism could be considered the most important specific mechanisms for Cd retention in the roots of T. repens.

Electric Field-Enhanced Cadmium Accumulation and Photosynthesis in a Woody Ornamental Hyperaccumulator—Lonicera japonica Thunb

The multi-system of electro-phytotechnology using a woody ornamental cadmium (Cd) hyperaccumulator (Lonicera japonica Thunb.) is a new departure for environmental remediation. The effects of four electric field conditions on Cd accumulation, growth, and photosynthesis of L. japonica under four Cd treatments were investigated. Under 25 and 50 mg L⁻¹ Cd treatments, Cd accumulation in L. japonica was enhanced significantly compared to the control and reached 1110.79 mg kg⁻¹ in root and 428.67 mg kg⁻¹ in shoots influenced by the electric field, especially at 2 V cm⁻¹, and with higher bioaccumulation coefficient (BC), translocation factor (TF), removal efficiency (RE), and the maximum Cd uptake, indicating that 2 V cm⁻¹ voltage may be the most suitable electric field for consolidating Cd-hyperaccumulator ability. It is accompanied by increased root and shoots biomass and photosynthetic parameters through the electric field effect. These results show that a suitable electric field may improve the growth, hyperaccumulation, and photosynthetic ability of L.japonica. Meanwhile, low Cd supply (5 mg L⁻¹) and medium voltage (2 V cm⁻¹) improved plant growth and photosynthetic capacity, conducive to the practical application to a plant facing low concentration Cd contamination in the real environment.

Methyl Jasmonate Alleviated the Adverse Effects of Cadmium Stress in Pea (Pisum sativum L.): A Nexus of Photosystem II Activity and Dynamics of Redox Balance

The accumulation of cadmium (Cd) in leaves reduces photosynthetic capacity by degrading photosynthetic pigments, reducing photosystem II activity, and producing reactive oxygen species (ROS). Though it was demonstrated that the application of Methyl Jasmonate (MeJA) induces heavy metal (HM) stress tolerance in plants, its role in adjusting redox balance and photosynthetic machinery is unclear. In this study, the role of MeJA in modulating photosystem II (PSII) activity and antioxidant defense system was investigated to reduce the toxic effects of Cd on the growth of pea (Pisum sativum L.) cultivars. One-week-old seedlings of three pea varieties were subjected to Cd stress (0, 50, 100 μm), and MeJA (0, 1, 5, 10 μm) was applied as a foliar spray for 2 weeks. Cadmium stress reduced the growth of all three pea varieties. Cadmium stress decreased photosynthetic pigments [Chl a (58.15%), Chl b (48.97%), total Chl (51.9%) and carotenoids (44.01%)] and efficiency of photosystem II [Fv/Fm (19.52%) and Y(II; 67.67%)], while it substantially increased Cd accumulation along with an increase in ROS (79.09%) and lipid peroxidation (129.28%). However, such adverse effects of Cd stress varied in different pea varieties. Exogenous application of MeJA increased the activity of a battery of antioxidant enzymes [superoxide dismutase (33.68%), peroxidase (29.75%), and catalase (38.86%)], improved photosynthetic pigments and PSII efficiency. This led to improved growth of pea varieties under Cd stress, such as increased fresh and dry weights of shoots and roots. In addition, improvement in root biomass by MeJA was more significant than that of shoot biomass. Thus, the mitigating effect of MeJA was attributed to its role in cellular redox balance and photosynthetic machinery of pea plants when exposed to Cd stress.

Cadmium Phytotoxicity, Tolerance, and Advanced Remediation Approaches in Agricultural Soils; A Comprehensive Review

Cadmium (Cd) is a major environmental contaminant due to its widespread industrial use. Cd contamination of soil and water is rather classical but has emerged as a recent problem. Cd toxicity causes a range of damages to plants ranging from germination to yield suppression. Plant physiological functions, i.e., water interactions, essential mineral uptake, and photosynthesis, are also harmed by Cd. Plants have also shown metabolic changes because of Cd exposure either as direct impact on enzymes or other metabolites, or because of its propensity to produce reactive oxygen species, which can induce oxidative stress. In recent years, there has been increased interest in the potential of plants with ability to accumulate or stabilize Cd compounds for bioremediation of Cd pollution. Here, we critically review the chemistry of Cd and its dynamics in soil and the rhizosphere, toxic effects on plant growth, and yield formation. To conserve the environment and resources, chemical/biological remediation processes for Cd and their efficacy have been summarized in this review. Modulation of plant growth regulators such as cytokinins, ethylene, gibberellins, auxins, abscisic acid, polyamines, jasmonic acid, brassinosteroids, and nitric oxide has been highlighted. Development of plant genotypes with restricted Cd uptake and reduced accumulation in edible portions by conventional and marker-assisted breeding are also presented. In this regard, use of molecular techniques including identification of QTLs, CRISPR/Cas9, and functional genomics to enhance the adverse impacts of Cd in plants may be quite helpful. The review's results should aid in the development of novel and suitable solutions for limiting Cd bioavailability and toxicity, as well as the long-term management of Cd-polluted soils, therefore reducing environmental and human health hazards.

Effects of Biogenic ZnO Nanoparticles on Growth, Physiological, Biochemical Traits and Antioxidants on Olive Tree In Vitro

Currently, there is an increasing interest in nanotechnology, since some nanomaterials can enhance crop growth, yield, nutritional status, and antioxidant defences. This work aimed to investigate for the first time the influence of zinc oxide nanoparticles (ZnO-NPs) on the in vitro growth and biochemical parameters of the olive tree (cv. Moraiolo). With this goal, biogenic ZnO-NPs (spherical shape and dimensions in the range of 10–20 nm), deriving from a green synthesis carried out with a Lemna minor L. extract were used. Different concentrations (0, 2, 6 and 18 mg L−1) of ZnO-NPs were added to the olive growth medium (OM substrate), and three sub-cultures of 45 days each were carried out. ZnO-NPs at 6 and 18 mg L−1 enhanced some growth parameters in the olive tree explants, such as the number of shoots, green fresh and total dry weight. Moreover, the abovementioned concentrations raised the chlorophyll a and b content and soluble protein. Finally, concerning the dosage applied, the treatments stimulated the content of carotenoids, anthocyanins, total phenol content (TPC), and the radical scavenging activity towards DPPH (2.2-diphenyl-1-picrylhydrazyl). In conclusion, this study highlighted that biogenic ZnO-NPs exerted beneficial effects on the olive tree explants in vitro, improving the effectiveness of the micropropagation technique.

Excess Zinc Supply Reduces Cadmium Uptake and Mitigates Cadmium Toxicity Effects on Chloroplast Structure, Oxidative Stress, and Photosystem II Photochemical Efficiency in Salvia sclarea Plants

Salvia sclarea L. is a Cd2+ tolerant medicinal herb with antifungal and antimicrobial properties cultivated for its pharmacological properties. However, accumulation of high Cd2+ content in its tissues increases the adverse health effects of Cd2+ in humans. Therefore, there is a serious demand to lower human Cd2+ intake. The purpose of our study was to evaluate the mitigative role of excess Zn2+ supply to Cd2+ uptake/translocation and toxicity in clary sage. Salvia plants were treated with excess Cd2+ (100 μM CdSO4) alone, and in combination with Zn2+ (900 μM ZnSO4), in modified Hoagland nutrient solution. The results demonstrate that S. sclarea plants exposed to Cd2+ toxicity accumulated a significant amount of Cd2+ in their tissues, with higher concentrations in roots than in leaves. Cadmium exposure enhanced total Zn2+ uptake but also decreased its translocation to leaves. The accumulated Cd2+ led to a substantial decrease in photosystem II (PSII) photochemistry and disrupted the chloroplast ultrastructure, which coincided with an increased lipid peroxidation. Zinc application decreased Cd2+ uptake and translocation to leaves, while it mitigated oxidative stress, restoring chloroplast ultrastructure. Excess Zn2+ ameliorated the adverse effects of Cd2+ on PSII photochemistry, increasing the fraction of energy used for photochemistry (ΦPSII) and restoring PSII redox state and maximum PSII efficiency (Fv/Fm), while decreasing excess excitation energy at PSII (EXC). We conclude that excess Zn2+ application eliminated the adverse effects of Cd2+ toxicity, reducing Cd2+ uptake and translocation and restoring chloroplast ultrastructure and PSII photochemical efficiency. Thus, excess Zn2+ application can be used as an important method for low Cd2+-accumulating crops, limiting Cd2+ entry into the food chain.

Potassium reduces oxidative stress in tanzania guinea grass under cadmium toxicity

Plants used for phytoextraction of metals need to tolerate toxicity conditions. Potassium (K) participates in physiological and biochemical processes that can alleviate toxicity by heavy metals, including cadmium (Cd). This study aimed to evaluate the effect of K on photosynthesis and on the changes in the antioxidant system of tanzania guinea grass [Panicum maximum Jacq. cv. Tanzania (syn. Megathyrsus maximus (Jacq,) B.K. Simon & S.W.L. Jacobs)] under Cd toxicity. Plants were grown in a greenhouse, in nutrient solution, in a randomized complete block design, arranged in a 3 × 4 factorial, with three replications. Plants were supplied with three K levels (0.4 [K deficiency], 6.0, and 11.6 mmol L^-1) and exposed to four Cd levels (0.0, 0.5, 1.0, and 1.5 mmol L^-1). Two plant growth periods were evaluated. High Cd level (1.5 mmol L^-1) led to a reduction in net photosynthesis (76%) by causing low stomatal conductance and losses in quantum efficiency of photosystem II. However, high K supply (11.6 mmol L^-1) increased the net photosynthesis by 15% in plants exposed to 1.0 mmol L^-1 Cd, due to upregulation of proline synthesis. Cd toxicity resulted in increases in lipid peroxidation and hydrogen peroxide concentration (35 and 50%; 25 and 30%, at first and second harvest, respectively) and reduction by 80-100% in activity of the antioxidant enzymes: superoxide dismutase, catalase, ascorbate peroxidase, guaiacol peroxidase, and glutathione reductase in the shoots of the grass. However, the high K supply (11.6 mmol L^-1) increased the activity of these enzymes (about 50-75%) and reduced lipid peroxidation (36%), restoring cellular homeostasis. Moreover, high K supply promoted a 25% increase in spermidine and spermine concentrations in the shoots. Therefore, K reduced the Cd-induced oxidative stress and increased the net photosynthesis in tanzania guinea grass by increasing the activity of antioxidant enzymes and proline and polyamines synthesis, which enhances the tolerance of this grass to Cd.