Hydrogen sulphide and nitric oxide mitigate the negative impacts of waterlogging stress on wheat (Triticum aestivum L.)

Nanoparticles synergy: Enhancing wheat (Triticum aestivum L.) cadmium tolerance with iron oxide and selenium

Nanotechnology is capturing great interest worldwide due to their stirring applications in various fields and also individual application of iron oxide nanoparticle (FeO - NPs) and selenium nanoparticles (Se - NPs) have been studied in many literatures. However, the combined application of FeO and Se - NPs is a novel approach and studied in only few studies. For this purpose, a pot experiment was conducted to examine various growth and biochemical parameters in wheat (Triticum aestivum L.) under the toxic concentration of cadmium (Cd) i.e., 50 mg kg-1 which were primed with combined application of two levels of FeO and Se - NPs i.e., 15 and 30 mg L-1 respectively. The results showed that the Cd toxicity in the soil showed a significantly (P < 0.05) declined in the growth, gas exchange attributes, sugars, AsA-GSH cycle, cellular fractionation, proline metabolism in T. aestivum. However, Cd toxicity significantly (P < 0.05) increased oxidative stress biomarkers, enzymatic and non-enzymatic antioxidants including their gene expression in T. aestivum. Although, the application of FeO and Se - NPs showed a significant (P < 0.05) increase in the plant growth and biomass, gas exchange characteristics, enzymatic and non-enzymatic compounds and their gene expression and also decreased the oxidative stress, and Cd uptake. In addition, individual or combined application of FeO and Se - NPs enhanced the cellular fractionation and decreases the proline metabolism and AsA - GSH cycle in T. aestivum. These results open new insights for sustainable agriculture practices and hold immense promise in addressing the pressing challenges of heavy metal contamination in agricultural soils.

Effect of hydrogen sulfide (H2S) on the growth and development of tobacco seedlings in absence of stress

BACKGROUND

Hydrogen sulfide (H2S) is a novel signaling molecule involved in the growth and development of plants and their response to stress. However, the involvement of H2S in promoting the growth and development of tobacco plants is still unclear.

RESULTS

In this study, we explored the effect of pre-soaking or irrigating the roots of tobacco plants with 0.0, 2.0, 4.0, 6.0, and 8.0 mM of sodium hydrosulfide (NaHS) on endogenous H2S production, antioxidant enzymatic and cysteine desulfhydrase activities, seed germination, agronomic traits, photosynthetic pigments contents, and root vigor. The results revealed that exogenous NaHS treatment could significantly promote endogenous H2S production by inducing gene expression of D/L-CD and the activities of D/L-CD enzymes. Additionally, a significant increase in the agronomic traits and the contents of photosynthetic pigments, and no significant difference in carotenoid content among tobacco plants treated with 0.0 to 8.0 mM of NaHS was observed. Additionally, a significant increase in the germination speed, dry weight, and vigor of tobacco seeds, whereas no significant effect on the percentage of seed germination was observed on NaHS treatment. Furthermore, NaHS treatment could significantly increase the activity of superoxide dismutase (SOD) and peroxidase (POD) enzymes, which reduces damage due to oxidative stress by maintaining reactive oxygen species homeostasis.

CONCLUSIONS

These results would aid in enhancing our understanding of the involvement of H2S, a novel signaling molecule to promote the growth and development of tobacco plants.

Unlocking the phytoremediation potential of organic acids: A study on alleviating lead toxicity in canola (Brassica napus L.)

Soil contamination with toxic heavy metals [such as lead (Pb)] is becoming a serious global problem due to the rapid development of the social economy. Organic chelating agents such as maleic acid (MA) and tartaric acid (TA) are more efficient, environmentally friendly, and biodegradable compared to inorganic chelating agents and they enhance the solubility, absorption, and stability of metals. To investigate this, we conducted a hydroponic experiment to assess the impact of MA (0.25 mM) and TA (1 mM) on enhancing the phytoremediation of Pb under its toxic concentration of 100 μM, using the oil seed crop canola (Brassica napus L.). Results from the present study showed that the Pb toxicity significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes and nutritional contents from the roots and shoots of the plants. In contrast, toxic concentration of Pb significantly (P < 0.05) increased oxidative stress indicators in term of malondialdehyde, hydrogen peroxide, and electrolyte leakage, increased enzymatic and non-enzymatic antixoidants and their specific gene expression and also increased organic acid exudation patter in the roots of B. napus. In addition, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double membranous organelles while Fourier-transform infrared (FTIR) spectroscopy showed an nveiled distinct peak variations in Pb-treated plants, when compared to control. Additionally, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that Pb toxicity significantly affected double-membrane organelles, while Fourier-transform infrared (FTIR) spectroscopy unveiled distinct peak variations in Pb-treated plants compared to the control. The negative impact of Pb toxicity can overcome the application of MA and TA, which ultimately increased plant growth and biomass by capturing the reactive oxygen species, and decreased oxidative stress in B. napus. With the application of MA and TA, the values of the bioaccumulation factor (BAF) and translocation factor (TF) exceeded 1, indicating that the use of MA and TA enhances the phytoremediation potential of B. napus under Pb stress conditions. This finding could be beneficial for field environment studies, especially when explored through in-depth genetic and molecular analysis.

Deciphering Physio-Biochemical Basis of Tolerance Mechanism for Sesame (Sesamum indicum L.) Genotypes under Waterlogging Stress at Early Vegetative Stage

Waterlogging represents a substantial agricultural concern, inducing harmful impacts on crop development and productivity. In the present study, 142 diverse sesame genotypes were examined during the early vegetative phase to assess their response under waterlogging conditions. Based on the severity of symptoms observed, 2 genotypes were classified as highly tolerant, 66 as moderately tolerant, 69 as susceptible, and 5 as highly susceptible. Subsequent investigation focused on four genotypes, i.e., two highly tolerant (JLT-8 and GP-70) and two highly susceptible (R-III-F6 and EC-335003). These genotypes were subjected to incremental stress periods (0 h, 24 h, 48 h, 72 h, and 96 h) to elucidate the biochemical basis of tolerance mechanisms. Each experiment was conducted as a randomized split-plot design with three replications, and the statistical significance of the treatment differences was determined using the one-way analysis of variance (ANOVA) followed by the Fisher least significant difference (LSD) test at p ≤ 0.05. The influence of waterlogging stress on morphological growth was detrimental for both tolerant and susceptible genotypes, with more severe consequences observed in the latter. Although adventitious roots were observed in both sets of genotypes above flooding levels, the tolerant genotypes exhibited a more rapid and vigorous development of these roots after 48 h of stress exposure. Tolerant genotypes displayed higher tolerance coefficients compared to susceptible genotypes. Furthermore, tolerant genotypes maintained elevated antioxidant potential, thereby minimizing oxidative stress. Conversely, susceptible genotypes exhibited higher accumulation of hydrogen peroxide (H2O2) and malondialdehyde content. Photosynthetic efficiency was reduced in all genotypes after 24 h of stress treatment, with a particularly drastic reduction in susceptible genotypes compared to their tolerant counterparts. Tolerant genotypes exhibited significantly higher activities of anaerobic metabolism enzymes, enabling prolonged survival under waterlogging conditions. Increase in proline content was observed in all the genotypes indicating the cellular osmotic balance adjustments in response to stress exposure. Consequently, the robust antioxidant potential and efficient anaerobic metabolism observed in the tolerant genotypes served as key mechanisms enabling their resilience to short-term waterlogging exposure. These findings underscore the promising potential of specific sesame genotypes in enhancing crop resilience against waterlogging stress, offering valuable insights for agricultural practices and breeding programs.

Exogenous Chemicals Used to Alleviate or Salvage Plants under Flooding/Waterlogging Stress: Their Biochemical Effects and Perspectives

Plant flooding/waterlogging stress (FWS) can be a threat to food security worldwide due to climate change. To mitigate its potential devastation, numerous exogenous chemicals (ECs) have been used to demonstrate their effectiveness on alleviating FWS for the last 20 years. This review has summarized the most recent findings on use of various ECs as either nutrients or regulatory substances on crop plants under FWS and their roles involved in improving root respiration of seedlings, optimizing nutritional status, synthesizing osmotic regulators, enhancing the activity of antioxidant enzymes, adjusting phytohormone levels, maintaining photosynthetic systems, and activating flood-tolerance related gene expressions. The effect of ESs on alleviating plants under FWS proves to be beneficial and useful but rather limited unless they are applied on appropriate crops, at the right time, and with optimized methods. Further research should be focused on use of ESs in field settings and on their potential synergetic effect for more FWS tolerance.

Role of Acetic Acid and Nitric Oxide against Salinity and Lithium Stress in Canola (Brassica napus L.)

In this study, canola (Brassica napus L.) seedlings were treated with individual and combined salinity and lithium (Li) stress, with and without acetic acid (AA) or nitric acid (NO), to investigate their possible roles against these stresses. Salinity intensified Li-induced damage, and the principal component analysis revealed that this was primarily driven by increased oxidative stress, deregulation of sodium and potassium accumulation, and an imbalance in tissue water content. However, pretreatment with AA and NO prompted growth, re-established sodium and potassium homeostasis, and enhanced the defense system against oxidative and nitrosative damage by triggering the antioxidant capacity. Combined stress negatively impacted phenylalanine ammonia lyase activity, affecting flavonoids, carotenoids, and anthocyanin levels, which were then restored in canola plants primed with AA and NO. Additionally, AA and NO helped to maintain osmotic balance by increasing trehalose and proline levels and upregulating signaling molecules such as hydrogen sulfide, γ-aminobutyric acid, and salicylic acid. Both AA and NO improved Li detoxification by increasing phytochelatins and metallothioneins, and reducing glutathione contents. Comparatively, AA exerted more effective protection against the detrimental effects of combined stress than NO. Our findings offer novel perspectives on the impacts of combining salt and Li stress.

Nitric oxide: An emerging warrior of plant physiology under abiotic stress

The natural environment of plants comprises a complex set of various abiotic stresses and their capability to react and survive under this anticipated changing climate is highly flexible and involves a series of balanced interactions between signaling molecules where nitric oxide becomes a crucial component. In this article, we focussed on the role of nitric oxide (NO) in various signal transduction pathways of plants and its positive impact on maintaining cellular homeostasis under various abiotic stresses. Besides this, the recent data on interactions of NO with various phytohormones to control physiological and biochemical processes to attain abiotic stress tolerance have also been considered. These crosstalks modulate the plant's defense mechanism and help in alleviating the negative impact of stress. While focusing on the diverse functions of NO, an effort has been made to explore the functions of NO-mediated post-translational modifications, such as the N-end rule pathway, tyrosine nitration, and S-nitrosylation which revealed the exact mechanism and characterization of proteins that modify various metabolic processes in stressed conditions. Considering all of these factors, the present review emphasizes the role of NO and its interlinking with various phytohormones in maintaining developmental processes in plants, specifically under unfavorable environments.

Nitric oxide mitigates vanadium toxicity in soybean (Glycine max L.) by modulating reactive oxygen species (ROS) and antioxidant system

Vanadium (V) induced hazardous effects posturing a serious concern on crop production as well as food security. However, the nitric oxide (NO)-mediated alleviation of V-induced oxidative stress in soybean seedlings is still unknown. Therefore, this research was designed to explore the effects of exogenous NO to mitigate the V-induced phytotoxicity in soybean plants. Our upshots disclosed that NO supplementation considerably improved the plant biomass, growth, and photosynthetic attributes by regulating the carbohydrates, and plants biochemical composition, which further improved the guard cells, and stomatal aperture of soybean leaves. Additionally, NO regulated the plant hormones, and phenolic profile which restricted the V contents absorption (65.6%), and translocation (57.9%) by maintaining the nutrient acquisition. Furthermore, it detoxified the excessive V contents, and upsurged the antioxidants defense mechanism to lower the MDA, and scavenge ROS production. The molecular analysis further verified the NO-based regulation of lipid, sugar production, and degradation as well as detoxification mechanism in the soybean seedlings. Exclusively, we elaborated very first time the behind mechanism of V-induced oxidative stress alleviation by exogenous NO, hence illustrating the NO supplementation role as a stress alleviating agent for soybean grown in V contaminated areas to elevate the crop development and production.

Application of silicon and sodium hydrosulfide alleviates arsenic toxicity by regulating the physio-biochemical and molecular mechanisms of Zea mays

Soil contamination with toxic heavy metals (such as arsenic (As)) is becoming a serious global problem due to rapid development of social economy, although the use of silicon (Si) and sodium hydrosulfide (NaHS) has been found effective in enhancing plant tolerance against biotic and abiotic stresses including the As toxicity. For this purpose, a pot experiment was conducted using the different levels of As toxicity in the soil, i.e., (0 mM (no As), 50, and 100 µM) which were also supplied with the different exogenous levels of Si, i.e., (0 (no Si), 1.5, and 3 mM) and also with the NaHS, i.e., (0 (no NaHS), 1, and 2 mM) on growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, antioxidant machinery (enzymatic and non-enzymatic antioxidants), and their gene expression, ion uptake, organic acid exudation, and As uptake of maize (Zea mays L.). Results from the present study showed that the increasing levels of As in the soil significantly (P < 0.05) decreased plant growth and biomass, photosynthetic pigments, gas exchange attributes, sugars, and nutritional contents from the roots and shoots of the plants. In contrast, increasing levels of As in the soil significantly (P < 0.05) increased oxidative stress indicators in terms of malondialdehyde, hydrogen peroxide, and electrolyte leakage and also increased organic acid exudation patter in the roots of Z. mays, although the activities of enzymatic antioxidants and the response of their gene expressions in the roots and shoots of the plants and non-enzymatic such as phenolic, flavonoid, ascorbic acid, and anthocyanin contents were initially increased with the exposure of 50 µM As, but decreased by the increasing the As concentration 100 µM in the soil. The negative impact of As toxicity can overcome the application of Si and NaHS, which ultimately increased plant growth and biomass by capturing the reactive oxygen species and decreased oxidative stress in Z. mays by decreasing the As contents in the roots and shoots of the plants. Our results also showed that the Si was more sever and showed better results when we compared with NaHS under the same treatment of As in the soil. Research findings, therefore, suggest that the combined application of Si and NaHS can ameliorate As toxicity in Z. mays, resulting in improved plant growth and composition under metal stress, as depicted by balanced exudation of organic acids.

Hydrogen sulfide upregulates the alternative respiratory pathway in mangrove plant Avicennia marina to attenuate waterlogging-induced oxidative stress and mitochondrial damage in a calcium-dependent manner

Hydrogen sulfide (H₂ S) is considered to mediate plant growth and development. However, whether H₂ S regulates the adaptation of mangrove plant to intertidal flooding habitats is not well understood. In this study, sodium hydrosulfide (NaHS) was used as an H₂ S donor to investigate the effect of H₂ S on the responses of mangrove plant Avicennia marina to waterlogging. The results showed that 24-h waterlogging increased reactive oxygen species (ROS) and cell death in roots. Excessive mitochondrial ROS accumulation is highly oxidative and leads to mitochondrial structural and functional damage. However, the application of NaHS counteracted the oxidative damage caused by waterlogging. The mitochondrial ROS production was reduced by H₂ S through increasing the expressions of the alternative oxidase genes and increasing the proportion of alternative respiratory pathway in the total mitochondrial respiration. Secondly, H₂ S enhanced the capacity of the antioxidant system. Meanwhile, H₂ S induced Ca²⁺ influx and activated the expression of intracellular Ca²⁺ -sensing-related genes. In addition, the alleviating effect of H₂ S on waterlogging can be reversed by Ca²⁺ chelator and Ca²⁺ channel blockers. In conclusion, this study provides the first evidence to explain the role of H₂ S in waterlogging adaptation in mangrove plants from the mitochondrial aspect.

In situ mapping of ion distribution profiles and gene expression reveals interactions between hypoxia and Mn2+/Fe2+ availability in barley roots

Flooding stress affects soil properties thus altering the availability, uptake, and transport of mineral nutrients in plant roots. Flooding stress also increases the amount of soluble Mn²⁺ and Fe²⁺ in the soil and their uptake by plants, causing elemental toxicity. However, as oxygen profiles in plant roots are not uniform, it is still unclear how soil flooding will affect Mn²⁺/Fe²⁺ absorption and distribution in different cell types and tissues. In this study, waterlogging sensitive barley variety NasoNijo (NN) and tolerant variety TX9425 (TX) were exposed to hypoxia, metal (Mn²⁺ and Fe²⁺), and combined hypoxia + metal treatment to map the in situ ion profiles at different regions of barley root. We found that combined hypoxia and metal stress causes significantly more reduction in plant biomass compared with the single submergence or metal stress. Despite this, more Fe and Mn were accumulated under metal stress condition than those under combined stress, regardless of variety. Cultivar NN absorbed more Fe and Mn than TX in the cortical cells of the root meristem and in the mature zone under metal stress which was also verified by histochemical detection. In the mature zone, the expressions of Fe and Mn transporter genes including HvADPRibase-Mn (Manganese-dependent ADP-ribose), HvZIP1 (zinc-regulated transporter /Fe-regulated transporter-like protein 1), HvYS1 (yellow stripe 1), HvNRAMP5 (Natural Resistance-Associated Macrophage Protein 5) were significantly downregulated under all three treatments in both barley varieties except HvADPRibase-Mn HvZIP1 cortex of TX were unchanged under metal stress. Interestingly, the transcripts of HvMTP1 (metal tolerance protein 1) were significantly downregulated by metal and combined stress in stele and upregulated by hypoxia and metal stress in cortex of TX, but not affected in NN. It is concluded that Fe and Mn absorption involving HvMTP1is associated with the extent of waterlogging tolerance in barley.

Say "NO" to plant stresses: Unravelling the role of nitric oxide under abiotic and biotic stress

Nitric oxide (NO) is a diatomic gaseous molecule, which plays different roles in different strata of organisms. Discovered as a neurotransmitter in animals, NO has now gained a significant place in plant signaling cascade. NO regulates plant growth and several developmental processes including germination, root formation, stomatal movement, maturation and defense in plants. Due to its gaseous state, it is unchallenging for NO to reach different parts of cell and counterpoise antioxidant pool. Various abiotic and biotic stresses act on plants and affect their growth and development. NO plays a pivotal role in alleviating toxic effects caused by various stressors by modulating oxidative stress, antioxidant defense mechanism, metal transport and ion homeostasis. It also modulates the activity of some transcriptional factors during stress conditions in plants. Besides its role during stress conditions, interaction of NO with other signaling molecules such as other gasotransmitters (hydrogen sulfide), phytohormones (abscisic acid, salicylic acid, jasmonic acid, gibberellin, ethylene, brassinosteroids, cytokinins and auxin), ions, polyamines, etc. has been demonstrated. These interactions play vital role in alleviating plant stress by modulating defense mechanisms in plants. Taking all these aspects into consideration, the current review focuses on the role of NO and its interaction with other signaling molecules in regulating plant growth and development, particularly under stressed conditions.

Biochar Stimulated Actual Evapotranspiration and Wheat Productivity under Water Deficit Conditions in Sandy Soil Based on Non-Weighing Lysimeter

The major climate-related hazard to worldwide agricultural productivity is drought, which is becoming more common because of ongoing climate change, especially in the arid and semi-arid regions. Herein, we investigated the influence of biochar soil application at 0, (B1), 7.5 ha^-1 (B2), and 15 t ha^-1 (B3) on the productivity and drought-tolerance indices of wheat (Triticum aestivum L., cv. Sakha 93) grown in sandy soil under irrigation levels of 100 (I1), 80 (I2), and 60% (I3) of crop evapotranspiration (ETc), as well as soil properties based on non-weighing lysimeter units. Increasing water deficiency significantly decreased the actual evapotranspiration (ETa) values. A growing biochar rate caused a significant increase in ETa values, water use efficiency, and wheat productivity compared to the untreated control. Additionally, biochar supplementation revealed an improvement in soil quality as measured by the reduction in the bulk density and hydraulic conductivity with an increase in the total porosity and void ratio of the experimental soil. The correlation analysis exhibited a highly significant and positive correlation (0.98 **) between biological yield and grain yield traits. Therefore, it may be stated that these traits are the most significant components of the evaluated grain yield in wheat plants. The productivity of I1 plants was not significantly different and slightly higher than that of I2 plants. Therefore, it can be recommended that exposed wheat plants cultivated in sandy soil with I2 × B3 treatment significantly provide the highest yield while saving 20% of the irrigation water.

Effects of exogenous taurine on growth, photosynthesis, oxidative stress, antioxidant enzymes and nutrient accumulation by Trifolium alexandrinum plants under manganese stress

Plants essentially require manganese (Mn) for their normal metabolic functioning. However, excess Mn in the cellular environment is detrimental to plant growth, development, and physio-biochemical functions. Taurine (TAU) is an amino acid with potent antioxidant and anti-inflammatory properties in animals and humans. However, no previous study has investigated the potential of TAU in plant metal stress tolerance. The current study provides some novel insights into the effect of TAU in modulating the defense system of Trifolium alexandrinum plants under Mn toxicity. Manganese toxicity resulted in higher oxidative stress and membrane damage through increased superoxide radical, hydrogen peroxide, malondialdehyde, and methylglyoxal generation alongside enhanced lipoxygenase (LOX) activity. Mn toxicity also resulted in limited uptake of potassium (K⁺), phosphorus (P), calcium (Ca²⁺), and increased the accumulation of Mn in both leaf and roots. However, TAU circumvented the Mn-induced oxidative stress by upregulating the activities of antioxidant enzymes (ascorbate peroxidase, peroxidase, catalase, glutathione reductase, glutathione-S-transferase, and superoxide dismutase) and levels of ascorbic acid, proline, anthocyanins, phenolics, flavonoids and glutathione (GSH). Taurine conspicuously improved the growth, photosynthetic pigments, hydrogen sulphide (H₂S), and nitric oxide (NO) levels of Mn stressed plants. Taurine also improved the uptake of K⁺, Ca²⁺, P and reduced the Mn content in stressed plants. Overall, exogenous taurine might be a suitable strategy to combat Mn stress in T. alexandrinum plants but applications at field levels for various crops and metal toxicities and economic suitability need to be addressed before final recommendations.

Zinc Oxide Nanoparticles and Their Biosynthesis: Overview

Zinc (Zn) is plant micronutrient, which is involved in many physiological functions, and an inadequate supply will reduce crop yields. Its deficiency is the widest spread micronutrient deficiency problem; almost all crops and calcareous, sandy soils, as well as peat soils and soils with high phosphorus and silicon content are expected to be deficient. In addition, Zn is essential for growth in animals, human beings, and plants; it is vital to crop nutrition as it is required in various enzymatic reactions, metabolic processes, and oxidation reduction reactions. Finally, there is a lot of attention on the Zn nanoparticles (NPs) due to our understanding of different forms of Zn, as well as its uptake and integration in the plants, which could be the primary step toward the larger use of NPs of Zn in agriculture. Nanotechnology application in agriculture has been increasing over recent years and constitutes a valuable tool in reaching the goal of sustainable food production worldwide. A wide array of nanomaterials has been used to develop strategies of delivery of bioactive compounds aimed at boosting the production and protection of crops. ZnO-NPs, a multifunctional material with distinct properties and their doped counterparts, were widely being studied in different fields of science. However, its application in environmental waste treatment and many other managements, such as remediation, is starting to gain attention due to its low cost and high productivity. Nano-agrochemicals are a combination of nanotechnology with agrochemicals that have resulted in nano-fertilizers, nano-herbicides, nano-fungicides, nano-pesticides, and nano-insecticides being developed. They have anti-bacterial, anti-fungal, anti-inflammatory, antioxidant, and optical capabilities. Green approaches using plants, fungi, bacteria, and algae have been implemented due to the high rate of harmful chemicals and severe situations used in the manufacturing of the NPs. This review summarizes the data on Zn interaction with plants and contributes towards the knowledge of Zn NPs and its impact on plants.

Differential Physio-Biochemical and Metabolic Responses of Peanut (Arachis hypogaea L.) under Multiple Abiotic Stress Conditions

The frequency and severity of extreme climatic conditions such as drought, salinity, cold, and heat are increasing due to climate change. Moreover, in the field, plants are affected by multiple abiotic stresses simultaneously or sequentially. Thus, it is imperative to compare the effects of stress combinations on crop plants relative to individual stresses. This study investigated the differential regulation of physio-biochemical and metabolomics parameters in peanut (Arachis hypogaea L.) under individual (salt, drought, cold, and heat) and combined stress treatments using multivariate correlation analysis. The results showed that combined heat, salt, and drought stress compounds the stress effect of individual stresses. Combined stresses that included heat had the highest electrolyte leakage and lowest relative water content. Lipid peroxidation and chlorophyll contents did not significantly change under combined stresses. Biochemical parameters, such as free amino acids, polyphenol, starch, and sugars, significantly changed under combined stresses compared to individual stresses. Free amino acids increased under combined stresses that included heat; starch, sugars, and polyphenols increased under combined stresses that included drought; proline concentration increased under combined stresses that included salt. Metabolomics data that were obtained under different individual and combined stresses can be used to identify molecular phenotypes that are involved in the acclimation response of plants under changing abiotic stress conditions. Peanut metabolomics identified 160 metabolites, including amino acids, sugars, sugar alcohols, organic acids, fatty acids, sugar acids, and other organic compounds. Pathway enrichment analysis revealed that abiotic stresses significantly affected amino acid, amino sugar, and sugar metabolism. The stress treatments affected the metabolites that were associated with the tricarboxylic acid (TCA) and urea cycles and associated amino acid biosynthesis pathway intermediates. Principal component analysis (PCA), partial least squares-discriminant analysis (PLS-DA), and heatmap analysis identified potential marker metabolites (pinitol, malic acid, and xylopyranose) that were associated with abiotic stress combinations, which could be used in breeding efforts to develop peanut cultivars that are resilient to climate change. The study will also facilitate researchers to explore different stress indicators to identify resistant cultivars for future crop improvement programs.

Individual and combinatorial effects of SNP and NaHS on morpho-physio-biochemical attributes and phytoextraction of chromium through Cr-stressed spinach (Spinacia oleracea L.)

Chromium (Cr) is a toxic heavy metal that contaminates soil and water resources after its discharge from different industries. A pot experiment was conducted to determine the effects of single and/or combined application of sodium nitroprusside (SNP) (250 μM) and sodium hydrogen sulfide (NaHS) (1 mM) on growth, photosynthetic pigments, gas exchange characteristics, oxidative stress biomarkers, antioxidant machinery (enzymatic and non-enzymatic antioxidants), ion uptake, organic acid exudation, and Cr uptake of spinach (Spinacia oleracea L.) exposed to severe Cr stress [Cr: 0 (no Cr), 150, and 300 μM]. Our results depicted that Cr addition to the soil significantly (P < 0.05) decreased plant growth and biomass, gas exchange attributes, and mineral uptake by S. oleracea when compared to the plants grown without the addition of Cr. However, Cr toxicity boosted the production of reactive oxygen species (ROS) by increasing the content of malondialdehyde (MDA), which is the indication of oxidative stress in S. oleracea, and was also manifested by hydrogen peroxide (H₂O₂) content and electrolyte leakage to the membrane-bound organelles. The results showed that the activities of various antioxidative enzymes, such as superoxidase dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX), and the content of non-enzymatic antioxidants, such as phenolic, flavonoid, ascorbic acid, and anthocyanin, initially increased with an increase in the Cr concentration in the soil. The results also revealed that the levels of soluble sugar, reducing sugar, and non-reducing sugar were decreased in plants grown under elevating Cr levels, but the accumulation of the metal in the roots and shoots of S. oleracea, was found to be increased, and the values of bioaccumulation factor were <1 in all the Cr treatments. The negative impacts of Cr injury were reduced by the application of SNP and NaHS (individually or combined), which increased plant growth and biomass, improved photosynthetic apparatus, antioxidant enzymes, and mineral uptake, as well as diminished the exudation of organic acids and oxidative stress indicators in roots of S. oleracea by decreasing Cr toxicity. Here, we conclude that the application of SNP and NaHS under the exposure to Cr stress significantly improved plant growth and biomass, photosynthetic pigments, and gas exchange characteristics; regulated antioxidant defense system and essential nutrient uptake; and balanced organic acid exudation pattern in S. oleracea.