Changes in ascorbate peroxidase, catalase, guaiacol peroxidase and superoxide dismutase activities in common bean (Phaseolus vulgaris) nodules under salt stress

Integrative use of biochar and biostimulants improves cadmium detoxification and yield in cotton

Dealing with abiotic stress is a challenge to maintaining sustainable agricultural productivity, especially for the dual stress of soil salinity and heavy metal contamination. A field experiment was conducted in a completely randomized factorial design to assess the combined effects of biochar (BC), plant growth-promoting microorganisms (PGPM), and seaweed extract (SWE) in mitigating cadmium (Cd) toxicity while promoting cotton growth in saline soils. The study included eight treatments: control (CK), single applications of SWE, PGPM, or BC, dual applications of BC + SWE, BC + PGPM, and PGPM + SWE, and a triple application (BC + PGPM + SWE). Results showed that the BC + PGPM + SWE treatment significantly improved soil quality by reducing the Na and Cd bioavailability by 31 % and 34 %, respectively, while enhancing soil organic matter, microbial biomass carbon, and soil enzymatic activity. Antioxidant defense mechanisms in cotton leaves were significantly induced, as indicated by enhanced activity of SOD, APX, DHAR and GR from 1.8-folds in SOD to 3.4-folds the control in GR. Multivariate analysis revealed that enzymatic and non-enzymatic antioxidants of the ascorbate-glutathione cycle seemed to play a key role in oxidative stress mitigation with maintenance of redox homeostasis and chelation of Cd, resulting in a reduction of 18 % and 56 % in Cd translocation factors from root to shoot, and from shoot to bolls, which contributing to a 65 % increase in cotton seed yield. This study demonstrates an integrative approach to enhancing the resilience of the soil and its productivity, thereby offering a scaling-up, eco-friendly strategy toward sustainable agriculture in degraded and stress-prone ecosystems.

Unraveling the role of κ-carrageenan on the combined effect of drought and chromium stress in wheat (Triticum aestivium L.)

Drought (D) and chromium (Cr) stress co-occur in agricultural fields due to the accumulation of excessive Cr in soils from industrial pollution and increasing frequency of water scarcity. Carrageenan (Car), a compound extracted from red seaweed, is an emerging biostimulant with multifaceted roles in plants. This study investigated the role of exogenous Car in mediating tolerance to D-, Cr-, and DCr-stress in wheat seedlings, aiming to elucidate the potential of Car in mitigating toxicity and promoting plant resilience. Wheat seedlings exposed to DCr-stress exhibited reduced growth and biomass production, along with elevated levels of reactive oxygen, carbonyl, and nitrogen species. Moreover, D-stress exacerbated Cr-toxicity, as demonstrated by principal component analysis (PCA), which showed a strong positive correlation between DCr-stress and stress marker parameters. This suggests that DCr-stress resulted in higher Cr uptake and increased oxidative damage compared to individual D- or Cr-stress, making DCr-stress more detrimental than either stress applied alone. However, Car priming ameliorated the toxic effects of DCr-stress and promoted the growth performance of DCr-stressed wheat seedlings. In PCA, the positive correlation of D + Car, Cr + Car, and DCr + Car treatments with growth and plant defense-related parameters suggests that Car-mediated improvement in stress tolerance can be attributed to reduced accumulation of toxic Cr, increased levels of total free amino acids and soluble sugars, enhanced antioxidant enzyme activity, elevated non-enzymatic antioxidant levels, higher phenolic and flavonoid content, and improved metal chelation and detoxification. Our results indicated Car is a potential and cost-effective biostimulant for managing D-, Cr-, or DCr-stress in wheat.

Red light induced seed germination and seedling growth by modulating antioxidant defense system, Rubisco, and NADPH oxidase activities in Capsicum frutescens

In this study, the impact of light-emitting diodes (LEDs) in different spectrums was investigated on the seed germination and post-germinative performance of Capsicum frutescens seedlings. The seeds were exposed to different LED lights (full spectrum, white, red, blue, and red-blue) for 0, 1, 2, and 4 h (h). The seeds were placed for a week in darkness to investigate germination, and then the growth mechanisms were studied in four-week-old seedlings. Results indicated that germination percentage was promoted markedly under 2 h red and full lights and also in 1 h blue, which was accompanied by the regulation of H2O2 level and NADPH oxidase (NOX) activity. Sprout growth and height were more heightened under 2 h red light, but their contents decreased considerably under blue light with a rising incubation time. Red light induced more biomass yield, chlorophyll (Chl) pigments, Chl a/b ratio and florescence in four-week-old seedlings. Blue light also increased Chl pigments, but decreased biomass yield by enhancing malondialdehyde (MDA) level. Increased growth in seedlings treated to red light was associated with upregulating Rubisco gene expressions (rbcL and rbcS) and its activity. Red and red-blue lights promoted the activity of superoxide dismutase, glutathione reductase, and ascorbate peroxidase enzymes to increase ascorbic acid (ASA) production in the ascorbate-glutathione cycle. Total phenolic (0.22 mg DAG g- 1 DW), ASA (89.58 mg 100 g- 1 FW) and capsaicinoids (2.73 mg g- 1 DW) contents were heightened under red light, while carotenoid (11.78 µg g- 1 FW) content was more accumulated under blue light. The findings of this study suggest red light modulates NOX activity and H2O2 level for inducing seed germination and seedling quality in C. frutescens, which can create important implications for the production of antioxidant metabolites and increase the cultivation area of this plant.

Useful or merely convenient: can enzymatic antioxidant activity be used as a proxy for abiotic stress tolerance?

During their lifespan, plants are often exposed to a broad range of stresses that change their redox balance and lead to accumulation of reactive oxygen species (ROS). The traditional view is that this comes with negative consequences to cells structural integrity and metabolism and, to prevent this, plants evolved a complex and well-coordinated antioxidant defence system that relies on the operation of a range of enzymatic and non-enzymatic antioxidants (AO). Due to the simplicity of measuring their activity, and in light of the persistent dogma that stress-induced ROS accumulation is detrimental for plants, it is not surprising that enzymatic AOs have often been advocated as suitable proxies for stress tolerance as well as potential targets for improving tolerance traits. However, there are a growing number of reports showing either no changes or even down-regulation of AO systems in stressed plants. Moreover, ROS are recognized now as important second messengers operating in both local and systemic signalling, synergistically interacting with the primary stressor, to regulate gene expression needed for optimal acclimatization. This work critically assesses the suitability of using enzymatic AOs as a proxy for stress tolerance or as a target for crop genetic improvement. It is concluded that constitutively higher AO activity may interfere with stress-induced ROS signalling and be a disadvantage for plant stress tolerance.

Translocation mechanism and the role of aerenchyma in nanoplastic translocation in Myriophyllum sp. "Roraima" and physiological responses

Nanoplastics have become a growing concern due to their potential impact on freshwater vegetation. The uptake, translocation, and effects of 0.05-µm nanoplastics on Myriophyllum sp. "Roraima" were investigated, along with the role of aerenchyma in nanoplastic transport. Microscopic observations revealed nanoplastic particle adsorption to the plant surface and entry into the roots and stems, with higher abundance and more dispersed distribution by direct contact. Nanoplastic particles were detected in the plant stem, primarily concentrated in regions adjacent to the aerenchyma. No morphological effects were observed. Induced changes in photosynthesis, including increased maximum quantum efficiency of photosystem II (Fv/Fm), decreased non-photochemical quenching (NPQ), decreased photosynthetic pigments, and increased photoprotective pigments, were recognized. Additionally, hydrogen peroxide levels and antioxidant enzyme activities varied in response to nanoplastic exposure. This study provides insights into the impact of nanoplastics on Myriophyllum sp. "Roraima" and has reviewed the underlying mechanisms, highlighting the role of aerenchyma in nanoplastic transport within the plant. Moreover, this study contributes to the understanding of the potential impacts of nanoplastic pollution on freshwater macrophytes while acknowledging the influence of phyto-anatomical structure on nanoplastic translocation.

Analysis of Stress Response Genes in Microtuberization of Potato Solanum tuberosum L.: Contributions to Osmotic and Combined Abiotic Stress Tolerance

Wild Solanum species have contributed many introgressed genes during domestication into current cultivated potatoes, enhancing their biotic and abiotic stress resistance and facilitating global expansion. Abiotic stress negatively impacts potato physiology and productivity. Understanding the molecular mechanisms regulating tuber development may help solve this global problem. We made a transcriptomic analysis of potato microtuberization under darkness, cytokinins, and osmotic stress conditions. A protein-protein interaction (PPI) network analysis identified 404 genes with high confidence. These genes were involved in important processes like oxidative stress, carbon metabolism, sterol biosynthesis, starch and sucrose metabolism, fatty acid biosynthesis, and nucleosome assembly. From this network, we selected nine ancestral genes along with eight additional stress-related genes. We used qPCR to analyze the expression of the selected genes under osmotic, heat-osmotic, cold-osmotic, salt-osmotic, and combined-stress conditions. The principal component analysis (PCA) revealed that 60.61% of the genes analyzed were associated with osmotic, cold-osmotic, and heat-osmotic stress. Seven out of ten introgression/domestication genes showed the highest variance in the analysis. The genes H3.2 and GAPCP1 were involved in osmotic, cold-osmotic, and heat-osmotic stress. Under combined-all stress, TPI and RPL4 were significant, while in salt-osmotic stress conditions, ENO1, HSP70-8, and PER were significant. This indicates the importance of ancestral genes for potato survival during evolution. The targeted manipulation of these genes could improve combined-stress tolerance in potatoes, providing a genetic basis for enhancing crop resilience.

Germination and biological adaptation approaches as salt-stress tolerance process in selected paddy cultivars under salinity stress

Cultivating productive paddy crops on salty soil to maximise production is a challenging approach to meeting the world's growing food demand. Thus, determining salinity tolerance rates in specific paddy cultivars is urgently needed. In this study, the salt tolerance traits of selected paddy cultivars, ADT45 and ADT39, were investigated by analysing germination, metabolites (pigments and biomolecules), and enzymatic (Superoxide dismutase (SOD), Catalase (CAT), and Peroxidase (POD) adaptation strategies as salt-stress tolerance mechanisms. This study found that salinity-induced reactive oxygen species (ROS) were efficiently detoxified by the antioxidant enzymes Superoxide dismutase (SOD), Catalase (CAT), and Peroxidase (POD) in ADT45 paddy varieties, followed by ADT39. Salinity stress had a significant impact on pigments and essential biomolecules in ADT45 and ADT39 paddy cultivars, including total chlorophyll, anthocyanin, carotenoids, ascorbic acid, hydrogen peroxide (H2O2), malondialdehyde, and proline. ADT45 demonstrated a significant relationship between H2O2 and antioxidant enzyme levels, followed by ADT39 paddy but not IR64. Morphological, physiological, and biochemical analyses revealed that ADT45, followed by ADT39, is a potential salt-tolerant rice cultivar.

Comparative role of calcium oxide nanoparticles and calcium bulk fertilizer to alleviate cadmium toxicity by modulating oxidative stress, photosynthetic performance and antioxidant-defense genes expression in alfalfa

Cadmium (Cd) toxicity poses a significant threat to soil health and sustainable food production. Its bioaccumulation in plant tissues induces phytotoxicity by affecting physiological and biochemical attributes, leading to a reduction in plant biomass and production. Recently, nanotechnology has emerged as a promising approach for addressing heavy metal toxicity in an eco-friendly manner to enhance crop production. However, the comparative role of foliar applied calcium oxide nanoparticles (CaO-NPs) and bulk calcium fertilizer under Cd stress in alfalfa remains unexplored. Herein, we studied the ameliorative role of CaO-NPs and bulk calcium (50 and 100 mg L-1) to alleviate Cd stress (30 mg kg-1) in alfalfa seedlings. Plants exposed to Cd exhibited significant decreases in morpho-physiological traits, gas exchange attributes, and pigment contents as well as increase in Cd bioaccumulation in plant tissues. Notably, exogenous application of CaO-NPs ameliorates the toxic impact of Cd by enhancing plant biomass (45%), fluorescence efficiency and gaseous exchange attributes. The maximum dose of CaO-NPs induced Cd-tolerance response accompanied by a significant increase in antioxidative enzyme activities, such as superoxide dismutase (SOD; 29%), peroxidase (POD; 41%), catalase (CAT; 36%) and ascorbate peroxidase (APX; 49%), which play positive roles in ROS scavenging. TEM examination further revealed the protective role of these NPs in averting Cd-induced damage to leaf ultrastructure and mesophyll cells. Furthermore, CaO-NPs had a substantial influence on both Cd and Ca2+ accumulation in plant tissues, while qRT‒PCR analysis demonstrated higher expression of antioxidant defense genes viz. Cu/ZnSOD (0.38 fold change (FC)), MtPOD (0.51 FC), MtCAT (0.61 FC) and MtAPX (0.79 FC) under CaO-NPs application, over Cd control. Overall, our findings suggested that exogenous CaO-NPs could be effective in alleviating the adverse effects of Cd on alfalfa seedlings to ensure food safety and support sustainable agriculture.

Exploring the impact of plant growth-promoting bacteria in alleviating stress on Aptenia cordifolia subjected to irrigation with recycled water in multifunctional external green walls

BACKGROUND

Rapid urbanization and population growth exert a substantial impact on the accessibility of drinking water resources, underscoring the imperative for wastewater treatment and the reuse of non-potable water in agriculture. In this context, green walls emerge as a potential solution to augment the purification of unconventional waters, simultaneously contributing to the aesthetic appeal and enjoyment of urban areas. This study aims to optimize water management in green walls by investigating the impact of bacterial strains on the biochemical properties and performance of the ornamental accumulator plant, Aptenia cordifolia, grown with various unconventional water sources. The experiments were designed as split plots based on a completely randomized block design with three replications. The main factor was recycled water with three levels (gray water, wastewater from the Kashfroud region of Mashhad, and urban water (control)). The sub-factor included different bacterial strains at four levels, composed of various bacteria combinations, (B1: Psedoumonas flucrecens + Azosporillum liposferum + Thiobacillus thioparus + Aztobactor chorococcum, B2: Paenibacillus polymyxa + Pseudomonas fildensis + Bacillus subtilis + Achromobacter xylosoxidans + Bacillus licheniform, B3: Pseudomonas putida + Acidithiobacillus ferrooxidans + Bacillus velezensis + Bacillus subtilis + Bacillus methylotrophicus + Mcrobacterium testaceum, and the control level without bacterial application (B0).

RESULT

The findings revealed significant differences at the 5% probability level across all morphophysiological traits, including plant height, the number and length of lateral branches, growth index, and plant coverage. Moreover, superior morphophysiological traits were observed in plants cultivated in substrates inoculated with wastewater irrigation. Substrates inoculated with bacteria exhibited the highest relative water content (RWC) and chlorophyll levels, coupled with the lowest relative saturation deficit (RSD), electrolyte leakage (EL), and carotenoid levels. Furthermore, plant growth-promoting bacteria (PGPB), from a biochemical perspective, were associated with increased carbohydrates, total protein, and anthocyanin. They also contributed to controlling oxidative stress caused by free radicals by enhancing the activity of antioxidant enzymes, such as guaiacol peroxidase (GPX), polyphenol oxidase (PPO), ascorbate peroxidase (APX), and peroxidase (POD), while reducing catalase enzyme (CAT) activity. This led to increased resistance to stress, as evidenced by a decrease in malondialdehyde and proline levels. The study concludes that the MIX B3, being both ecofriendly and economical, represents an effective strategy for mitigating the adverse effects of wastewater on plants.

CONCLUSION

This study showed that plant irrigation using wastewater increases the levels of proline, phenols and oxidative stress. However, the application of plant growth promoting bacteria (PGPB) reduced oxidative damage by increasing antioxidant activity and decreasing proline and phenol levels. These findings show the potential of bacterial treatments to improve plant growth and reduce adverse effects of recycled water irrigation.

Antioxidative and Metabolic Responses in Canola: Strategies with Wood Distillate and Sugarcane Bagasse Ash for Improved Growth under Abiotic Stress

In the context of increasing agricultural challenges posed by soil salinity and drought stress, the main importance of the present study was to evaluate some novel treatments for improving canola productivity and resilience by applying wood distillate (WD) in combination with bagasse ash (SBA). A two-year field experiment using a split plot design was conducted and evaluated several physiological and biochemical parameters under different irrigation regimes conducted at 80% and 50% field capacity. While there were considerable moderation effects of SBA and WD on soil salinity, expressed as exchangeable sodium percentage (ESP), under both well-irrigated and drought conditions, more importantly, the ESP was reduced to 31% under drought stress with combined WD and SBA applications over any single factor. WD and SBA treatments of canola leaves showed reduced Na content with increased K levels, and the plants maintained physiological attributes-chlorophyll content, stomatal conductance, and relative water content-to the level of controls of well-irrigation. Besides, they significantly alleviated oxidative stress by decreasing the hydrogen peroxide (H2O2), malondialdehyde (MDA), and electrolyte leakage (EL) levels and increasing the activities of antioxidant enzymes like superoxide dismutase (SOD) and ascorbate peroxidase (APX). Nonenzymatic antioxidants such as total soluble sugars (TSS), total soluble proteins (TSP), total phenolic content (TPC), and total flavonoid content (TFC) were significantly increased under stress conditions with a special accent on combined treatment, whereas the levels of proline and GB that increased in alignment with drought reduced under the combined application. Various growth parameters of plants like plant height, number of branches, and siliques per plant were significantly improved with WD and SBA under drought stress. Principal component analysis (PCA) and Pearson correlation further confirmed the relationships among these parameters and thus underpinned that WD and SBA can evoke a synergistic effect to enhance growth promotion and stress tolerance in canola. This, therefore, infers that the combined application of WD and SBA can be key, offering very high potential as viable options to better canola productivity under adverse environmental conditions.

Comprehensive analysis of pepper (Capsicum annuum) RAV genes family and functional identification of CaRAV1 under chilling stress

BACKGROUND

Despite its known significance in plant abiotic stress responses, the role of the RAV gene family in the response of Capsicum annuum to chilling stress remains largely unexplored.

RESULTS

In this study, we identified and characterized six members of the CaRAV gene subfamily in pepper plants through genome-wide analysis. Subsequently, the CaRAV subfamily was classified into four branches based on homology with Arabidopsis thaliana, each exhibiting relatively conserved domains within the branch. We discovered that light response elements accounted for the majority of CaRAVs, whereas low-temperature response elements were specific to the NGA gene subfamily. After pepper plants were subjected to chilling stress, qRT‒PCR analysis revealed that CaRAV1, CaRAV2 and CaNGA1 were significantly induced in response to chilling stress, indicating that CaRAVs play a role in the response to chilling stress. Using virus-induced gene silencing (VIGS) vectors, we targeted key members of the CaRAV gene family. Under normal growth conditions, the MDA content and SOD enzyme activity of the silenced plants were slightly greater than those of the control plants, and the REC activity was significantly greater than that of the control plants. The levels of MDA and electrolyte leakage were greater in the silenced plants after they were exposed to chilling stress, and the POD and CAT enzyme activities were significantly lower than those in the control, which was particularly evident under repeated chilling stress. In addition, the relative expression of CaPOD and CaCAT was greater in V2 plants upon repeated chilling stress, especially CaCAT was significantly greater in V2 plants than in the other two silenced plants, with 3.29 and 1.10 increases within 12 and 24 h. These findings suggest that CaRAV1 and CaNGA1 positively regulate the response to chilling stress.

CONCLUSIONS

Silencing of key members of the CaRAV gene family results in increased susceptibility to chilling damage and reduced antioxidant enzyme activity in plants, particularly under repeated chilling stress. This study provides valuable information for understanding the classification and putative functions of RAV transcription factors in pepper plants.

Floral scents, specialized metabolites and stress-response activities in Heritiera fomes and Bruguiera gymnorrhiza from Sundarban mangrove ecosystem

Floral biochemistry and stress physiology is an underexplored aspect of mangroves, which should be investigated as part of preservation and restoration efforts. A thriving true mangrove tree (Bruguiera gymnorrhiza (L.) Lamk.) and a threatened mangrove-associate species (Heritiera fomes Buch. Ham.) were studied in the Sundarban region of India for seasonal variations in floral odours, non-volatile phytochemicals, antioxidant enzyme activities, and surface water chemistry in surrounding habitat. Both species were found to exhibit significant differences in floral volatilomes, protein contents, antioxidant enzyme activities, total flavonoids, and total phenolic contents between spring and autumn blooms. The bird-pollinated flowers of B. gymnorrhiza also showed considerable seasonal differences in floral anthocyanin and proline contents, indicating vulnerability of the post-anthesis open flowers to environmental factors. Contrarily to previous findings, B. gymnorrhiza floral bouquet appeared to be enriched in various classes of volatiles - dominated by sulphurous compounds in bud stage and terpenoids in open stage. Floral anthocyanins, contributing to the striking colouration of the calyx, were found to comprise cyanidin and delphinidin derivatives. Other glycosides of cyanidin and delphinidin were detected in H. fomes flowers, contributing to visual guides to potential food rewards for pollinating insects. Floral tissue in H. fomes was found to be protected by densely overlapping layers of stellate trichomes containing sesquiterpenoids as phytoprotectants. Comparison of the two floral species suggested that H. fomes flowering is optimized to oligohaline (but not freshwater) vernal conditions; whereas B. gymnorrhiza blooms are adapted for biologically enriched (including abundant herbivores and microbial growth), mesohaline forest habitats.

An evaluation of conventional and nature-based technologies for controlling antibiotic-resistant bacteria and antibiotic-resistant genes in wastewater treatment plants

Antibiotic resistance is a globally recognized health concern which leads to longer hospital stays, increased morbidity, increased mortality, and higher medical costs. Understanding how antibiotic resistance persists and exchanges in environmental systems like soil, water, and wastewater are critically important for understanding the emergence of pathogens with new resistance profiles and the subsequent exposure of people who indirectly/directly come in contact with these pathogens. There are concerns about the widespread application of prophylactic antibiotics in the clinical and agriculture sectors, as well as chemicals/detergents used in food and manufacturing industries, especially the quaternary ammonium compounds which have been found responsible for the generation of resistant genes in water and soil. The rates of horizontal gene transfer increase where there is a lack of proper water/wastewater infrastructure, high antibiotic manufacturing industries, or endpoint users - such as hospitals and intensive agriculture. Conventional wastewater treatment technologies are often inefficient in the reduction of ARB/ARGs and provide the perfect combination of conditions for the development of antibiotic resistance. The wastewater discharged from municipal facilities may therefore be enriched with bacterial communities/pathogens and provide a suitable environment (due to the presence of nutrients and other pollutants) to enhance the transfer of antibiotic resistance. However, facilities with tertiary treatment (either traditional/emerging technologies) provide higher rates of reduction. This review provides a synthesis of the current understanding of wastewater treatment and antibiotic resistance, examining the drivers that may accelerate their possible transmission to a different environment, and highlighting the need for tertiary technologies used in treatment plants for the reduction of resistant bacteria/genes.

Reduced glutathione and raffinose lengthens postharvest storage of cassava root tubers by improving antioxidant capacity and antibiosis

Cassava is an ideal food security crop in marginal and drought environment. However, the post-harvest storage of cassava is urgent problem to be resolved. In this study, the storage tolerant and non-tolerant cassava were screened by measuring the change of Peroxidase (POD), Superoxide dismutase (SOD), Catalase (CAT) and Malondialdehyde (MDA) in seven cultivars of cassava. Compared with other cultivars, the cultivar of SC14 showed the highest level of SOD, MDA and POD respectively at 0 day, 12 day and 9 day postharvest while exhibited lowest level of CAT at 0 day postharvest, indicating the strongest antioxidant capability and storage tolerance. In contrast, GR15231, termed as storage non-tolerance cultivars, showed lowest SOD and POD at 12 day and kept a relative high level of CAT at 12 day post-harvest. In addition, SC14 has higher level of starch and dry substance than GR15231. Mass spectrum was performed for SC14 and GR15231 to explore the key metabolites regulating the storage tolerance of cassava. The results showed that the expression of glutathione (reduced) and raffinose was significantly decreased at 12 day post-harvest both in tolerant SC14 and non-tolerant GR15231. Compared with GR15231, SC14 showed higher level of raffinose both at 0 and 12 day post-harvest, indicating that raffinose may be the potential metabolites protecting SC14 cultivar from deterioration post-harvest. Additionally, raffinose ratio of SC14a/SC14b was five times less than that of GR15231a/GR15231b, reflecting the slower degradation of raffinose in SC14 cultivar compared with GR15231 cultivar. In conclusion, the antioxidant microenvironment induced by reduced glutathione and higher level of raffinose in SC14 cultivar might be the promising metabolites to improve its antioxidant capacity and antibiosis and thus maintained the quality of Cassava root tubers.

Antioxidant enzymes of Pseudochlorella pringsheimii under two stressors: variation of SOD Isoforms activity

Algae are always facing the challenge of exposure to different stress conditions, therefore raising challenges of adaptation for survival. In this context, the growth and the antioxidant enzymes of the green stress-tolerant alga Pseudochlorella pringsheimii were investigated under two environmental stresses viz. iron and salinity. The number of algal cells was moderately increased by iron treatment in the range of 0.025-0.09 mM of iron, yet, the number of cells decreased at high iron concentrations (0.18 to 0.7 mM Fe). Furthermore, the different NaCl concentrations (8.5-136.0 mM) had an inhibitory effect on the algal cell number, compared to the control.The superoxide dismutase (SOD) showed three isoforms namely; Mn, Fe, and Cu/Zn SOD. The in gel and in vitro (tube-test) activities of FeSOD were higher compared with the other SOD isoforms. The activity of total SOD and its isoforms increased significantly by the different concentrations of Fe and non-significantly by NaCl. The maximum SOD activity was recorded at 0.7 mM Fe (67.9% above control). The relative expression of FeSOD was high under iron and NaCl at 8.5 and 34 mM, respectively. However, FeSOD expression was reduced at the highest NaCl tested concentration (136 mM). In addition, the antioxidant enzyme activity of catalase (CAT) and peroxidase (POD) were accelerated by increasing iron and salinity stress which indicates the essential role of these enzymes under stress. The correlation between the investigated parameters was also investigated. A highly significant positive correlation between the activity of total SOD and its isoforms, and with the relative expression of FeSOD was observed.

The comparative effects of manganese nanoparticles and their counterparts (bulk and ionic) in Artemisia annua plants via seed priming and foliar application

The world has experienced an unprecedented boom in nanotechnology. Nanoparticles (NPs) are likely to act as biostimulants in various plants due to having high surface/volume value. However, understanding the actual effect of NPs is essential to discriminate them from other counterparts in terms of being applicable, safe and cost-effective. This study aimed to assay the impact of manganese(III) oxide (Mn₂O₃)-NPs via seed-priming (SP) and a combination of SP and foliar application (SP+F) on Artemisia. annua performance at several times intervals and comparison with other available manganese (Mn) forms. Our findings indicate that SP with MnSO₄ and Mn₂O₃-NPs stimulates the processes that occur prior to germination and thus reduces the time for radicle emergence. In both applications (i.e., SP and +F), none of the Mn treatments did show adverse phytotoxic on A. annua growth at morpho-physio and biochemical levels except for Mn₂O_3, which delayed germination and further plant growth, subsequently. Besides, from physio-biochemical data, it can be inferred that the general mechanism mode of action of Mn is mainly attributed to induce the photosynthetic processes, stimulate the superoxide dismutase (SOD) activity, and up-regulation of proline and phenolic compounds. Therefore, our results showed that both enzymatic and non-enzymatic antioxidants could be influenced by the application of Mn treatments in a type-dependent manner. In general, this study revealed that Mn₂O₃-NPs at the tested condition could be used as biostimulants to improve germination, seedling development and further plant growth. However, they are not as effective as MnSO₄ treatments. Nonetheless, these findings can be used to consider and develop Mn₂O₃-NPs priming in future studies to improve seed germination and seedling quality in plants.

Physio-biochemical characterization of wheat genotypes under temperature stress

Thermal stress is a major abiotic stress in wheat and is highly complex in mechanism. A large area in northwestern plain zones (NWPZ), which is the wheat bowl of India is affected by heat stress. Climate change also causes an abrupt increase in temperature at different growth stages of wheat. Thus, wiser selection of stress tolerant varieties is an important strategy to combat the climate change effect. The present study aims for physiological and biochemical screening of timely sown NWPZ wheat varieties (WB2, HD3086, DBW88, DPW621-50, DBW17, HD2967 and PBW550) of India for their thermal stress tolerance along with heat tolerant (RAJ3765) and susceptible checks (RAJ4014) at seedling stage. The experiment was conducted in completely randomized design under controlled laboratory condition and heat stress was induced at 37 °C at seedling stage. Later different physio-biochemical traits were studied in both control and stress seedlings. All traits exhibited significant variations among genotypes under heat stress condition. Root and shoot weight, relative water content, chlorophyll content index and chlorophyll fluorescence reduced significantly, whereas membrane leakage, osmotic potential, catalase, ascorbate peroxidase, guaiacol peroxidase, malondialdehyde content and proline content were increased in stress plants. A tolerance matrix was prepared based on stress response of the genotypes for each trait and a final tolerance score was given to each genotype. Based on this tolerance matrix, DBW88 and PBW550 were identified as tolerant, DPW621-50, DBW17 and HD2967 as moderately susceptible and HD3086 and WB2 as susceptible to heat stress. Earlier studies parade that seedling level stress tolerance has high correlation with adult level stress tolerance under field condition in wheat. Hence, this study helps in wiser selection of varieties for sowing in NWPZ based on weather forecast of the location for creating varietal mosaic in context of climate change.

A novel long noncoding RNA CIL1 enhances cold stress tolerance in Arabidopsis

With the intensification of global warming, extreme weather events have occurred more frequently, among which cold stress has become one of the major environmental factors that restrict global crop yield and production. Multiple long noncoding RNAs (lncRNAs) have been predicted or recognized in the plant response to cold stress, however, the molecular biological functions of most of these RNAs are still poorly understood. Here, we identified a novel lncRNA, COLD INDUCED lncRNA 1 (CIL1), as a positive regulator of the plant response to cold stress in Arabidopsis. CIL1 was significantly induced when the plant was exposed to cold stress. Moreover, knockdown mutants showed more sensitivity to cold stress than the wild type did, accompanied by an increased content of endogenous ROS (reactive oxygen species) and reduced osmoregulatory substances. Genome-wide transcriptome analysis indicated that 256 genes were downregulated and 34 genes were upregulated in cil1 mutants under cold stress, which were mainly involved in hormone signal transduction, ROS homeostasis and glucose metabolism. Our study implies that CIL1 has a positive effect on the plant response to cold stress by regulating the expression of multiple stress-related genes during the seedling stage.

B2, an abscisic acid mimic, improves salinity tolerance in winter wheat seedlings via improving activity of antioxidant enzymes

Salinity severely inhibits growth and reduces yield of salt-sensitive plants like wheat, and this effect can be alleviated by plant growth regulators and phytohormones, among which abscisic acid (ABA) plays a central role in response to various stressful environments. ABA is highly photosensitive to light disruption, which this limits its application. Here, based on pyrabactin (a synthetic ABA agonist), we designed and synthesized a functional analog of ABA and named B2, then evaluated its role in salt resistance using winter wheat seedlings. The phenotypes showed that B2 significantly improved the salt tolerance of winter wheat seedlings by elevating the biomass. The physiological analysis found that B2 treatment reduced the generation rate of O₂ ^-, electrolyte leakage, the content of proline, and the accumulation of malonaldehyde (MDA) and H₂O₂ and also significantly increased the contents of endogenous hormones zeatin riboside (ZA) and gibberellic acid (GA). Further biochemical analysis revealed that the activities of various antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), were enhanced by B2, and the activities of antioxidase isozymes SOD3, POD1/2, and APX1/2 were particularly increased, largely resembling ABA treatment. The abiotic stress response-related gene TaSOS1 was significantly upregulated by B2, while the TaTIP2;2 gene was suppressed. In conclusion, an ABA analog B2 was capable to enhance salt stress tolerance in winter wheat seedlings by stimulating the antioxidant system, providing a novel regulator for better survival of crops in saline soils and improving crop yield.

Whole plant response of Pongamia pinnata to drought stress tolerance revealed by morpho-physiological, biochemical and transcriptome analysis

BACKGROUND

Pongamia is considered an important biofuel species worldwide. Drought stress in the early growth stages of Pongamia influences negatively on the germination and seedling development. Due to lack of cultivar stability under drought stress conditions, establishment of successful plantation in drought hit areas becomes a major problem. To address this issue, drought stress response of four Pongamia genotypes was studied at morphological, physio-chemical and transcriptome levels.

METHODS AND RESULTS

Drought stress was levied by limiting water for 15 days on three months old seedlings of four genotypes. A significant effect of water stress was observed on the traits considered. The genotype NRCP25 exhibited superior morpho-physiological, biochemical drought responses. Also, the genotype had higher root length, photosynthetic pigments, higher antioxidant enzymes and solute accumulation compared to other genotypes. In addition, transcript profiling of selected drought responsive candidate genes such as trehalose phosphate synthase 1 (TPS1), abscisic acid responsive elements-binding protein 2 (ABF2-2), heat shock protein 17 (HSP 17 kDa), tonoplast intrinsic protein 1 (TIP 1-2), zinc finger homeodomain protein 2 (ZFP 2), and xyloglucan endotransglucolase 13 (XET 13) showed only up-regulation in NRCP25. Further, the transcriptome responses are in line with key physio-chemical responses exhibited by NRCP25 for drought tolerance.

CONCLUSIONS

As of now, there are no systematic studies on Pongamia drought stress tolerance; therefore this study offers a comprehensive understanding of whole plant drought stress responsiveness of Pongamia. Moreover, the results support important putative trait indices with potential candidate genes for drought tolerance improvement of Pongamia.

Presence of polystyrene microplastics in Cd contaminated water promotes Cd removal by nano zero-valent iron and ryegrass (Lolium Perenne L.)

Microplastics, as emerging contaminants, have attracted widespread attention for their increasing detection frequency in aquatic environment. It has been reported that microplastics may co-presence with heavy metals in water, which might have impact on heavy metals removal in water. Furthermore, the effects of microplastics on the co-remediation efficiency of plants with engineered nanomaterials are ambiguous. To this end, this study was dedicated to unveil the intrinsic effects of polystyrene microplastics (PSMPs) on the cadmium (Cd) removal efficiency by co-remediation of ryegrass (Lolium perenne L.) and three engineered nanomaterials, respectively were nano-zerovalent iron (nZVI), carboxymethylcellulose-modified-nZVI (C-nZVI) and sulfidated nZVI (S-nZVI). Significant changes were observed in Cd content, plant biomass, chlorophyll b and antioxidant enzymes. It was surprising to find that with the treatment of nZVI or C-nZVI, polystyrene microplastics would enter plants roots, and these plants were found to contain more Cd among all series. Accordingly, four possible mechanisms were proposed to explain why plants that observed the internalization of PSMPs contained more Cd. This work reveals the impact of coexisting microplastics in water on Cd remediation efficiency and provides new insights into the entry of polystyrene microplastics into plant roots.

Ultrastructure, adaptability, and alleviation mechanisms of photosynthetic apparatus in plants under waterlogging: A review

Photosynthesis is a process highly sensitive to various abiotic and biotic stresses in plants. Among them, the major abiotic stress, waterlogging, affects the crop's growth and productivity. Under waterlogging, the photosynthetic apparatus of plants was destroyed. Waterlogging reduced chlorophyll content and the net photosynthetic rate. Therefore, this updated review summarized the effect of waterlogging on chloroplast ultrastructure, photosynthetic characteristics, and chlorophyll fluorescence attributes of plant species. By studying various research papers, we found that intercellular concentration of available carbon dioxide in mesophyll cells, assimilation of carbon, and the net photosynthetic ratio declined under waterlogging. The chlorophyll fluorescence efficiency of plants decreased under waterlogging. Thus, the study of photosynthesis in plants under waterlogging should be done with respect to changing climate. Moreover, the recognition of photosynthetic characteristics present in tolerant species will be beneficial for designing the waterlogging-tolerant crop plant in changing environments.

RsmA3 modulates RpoS through the RetS-Gac-Rsm signaling pathway in response to H2 O2 stress in the phytopathogen Pseudomonas syringae

Reactive oxygen species are a fatal challenge to the plant pathogenic bacterium Pseudomonas syringae. In this study, we reveal that the global regulatory protein RsmA3 from the RetS-Gac/Rsm signaling pathway modulates RpoS in the early-log growth phase in the P. syringae wild-type strain MB03, thereby regulating oxidative tolerance to H₂ O₂ and ultimately affecting pathogenicity to the host plant. Following increased H₂ O₂ by external addition or endogenous induction by menadione, the resistance of the mutant strain ΔretS to H₂ O₂ is significantly enhanced due to rapid increases in the transcription of Rsm-related non-coding small RNAs (nc sRNAs), a sigma factor RpoS, and H₂ O₂ -detoxifying enzymes. Moreover, the ΔretS mutant is significantly less pathogenic in cucumber leaves. Seven Rsm-related nc sRNAs (namely, rsmZ, rsmY, and rsmX_1-5 ) show functional redundancy in the RetS-Gac-Rsm signaling pathway. External addition of H₂ O₂ stimulates increases in the transcription of both rsmY and rsmZ. Thus, we propose a regulatory model of the RetS-Gac-Rsm signaling pathway in P. syringae MB03 for the regulation of H₂ O₂ tolerance and phytopathogenicity in the host plant.

The impact of indigenous soil yeasts inoculation on bean (Phaseolus vulgaris) growth

To determine whether the use of soil yeasts as inoculum would intervene in improving bean (Phaseolus vulgaris) growth and its symbiotic parameters, various experiments have been carried out. The effect of inoculation by soil yeasts Meyerozyma guilliermondii GP MT258984, Debaryomyces hansenii DFA MT259039, Rhodotorula mucilaginosa LIA MT259358, Rhodotorula mucilaginosa LC MT252049, along with the strain Saccharomyces cerevisiae in their cell or metabolite forms, was investigated in non-sterile (sand) and agricultural substrates (soil), in association or not with mycorrhizal fungi. The results showed that the yeast could have a beneficial effect on the bean biomass directly without increasing its nodulation and mycorrhization, or indirectly by improving those symbiotic parameters. They also revealed a very important ecological aspect and the possibility of inoculating with indigenous soil yeasts to increase the number of fertilising microorganisms, such as mycorrhizae and rhizobia, without resorting to introducing exogenous strains.

Impact of Two Strains of Rhizobium leguminosarum on the Adaptation to Terminal Water Deficit of Two Cultivars Vicia faba

Drought stress has become one of the most uncontrolled and unpredictable constraints on crop production. The purpose of this study was to evaluate the impacts of two different Rhizobium leguminosarum strains on terminal drought tolerance induction in two faba bean genotypes cultivated in Algeria, Aquadulce and Maltais. To this end, we measured physiological parameters—osmoprotectants accumulation, oxidative stress markers and enzyme activities—to assess the effect of R. leguminosarum inoculation on V. faba under terminal water deficiency conditions in greenhouse trials. Upregulation of anti-oxidative mechanisms and production of compatible solutes were found differentially activated according to Rhizobium strain. Drought stress resilience of the Maltais variety was improved using the local Rhizobium strain OL13 compared to the common strain 3841. Symbiosis with OL13 strain leads in particular to a much better production of proline and soluble sugar in nodules but also in roots and leaves of Maltais plant. Even if additional work is still necessary to decipher the mechanism by which a Rhizobium strain can affect the accumulation of osmoprotectants or cellular redox status in all the plants, inoculation with selected Rhizobium could be a promising strategy for improving water stress management in the forthcoming era of climate change.

Radiochemical Evidence for the Contribution of Chemotyped Siderophore Producing Bacteria Towards Plant Iron Nutrition

Fe deficiency is a major challenge that limits agricultural productivity and is a serious human health concern worldwide. Under iron-limiting conditions soil microorganisms produce siderophores, that chelates Fe³⁺ (ferric) and make it available to the plants. Selection of efficient siderophore producing bacteria and establishing their role in enhancing iron uptake is a strategic approach for improving plant nutrition. Hence 3 efficient isolates Pantoea agglomerans, Pseudomonas plecoglossida and Lactococcus lactis, selected from a repository of 154 bacteria, producing catecholate, hydroxamate and carboxylate siderophores, respectively, were assessed for Fe chelation efficiency using ⁵⁹Fe and their role in plant biometric parameters, Fe uptake and antioxidant enzymes with tomato (Strategy I) and wheat (Strategy II) test plants under hydroponic system. Cell-free siderophore preparation (Sid) improved plant parameters and iron nutrition more efficiently than bacterial inoculants. Pantoea agglomerans was proven best as its ⁵⁹Fe-bound siderophore complex showed the highest uptake of 4.25 and 1.59 Bq plant^-1 in wheat and tomato, respectively. Further, the Fe-starved plants (1 µm Fe-EDTA) showed around two-fold higher ⁵⁹Fe uptake than those raised under Fe-sufficient condition (100 µm Fe-EDTA). Results indicated that probably the bacterial mediated iron translocation in plants is Strategy III, complementing both Strategy I and II by facilitating higher availability of chelated Fe to plant reductases directly and/or through ligand exchange with phytosiderophores, respectively. This study highlights the need for integration of siderophore based formulations in INM strategies for enhancing plant iron content to address the Fe deficiency challenge of the soil and human nutrition.

Titanium dioxide nanoparticle is involved in mitigating NaCl-induced Calendula officinalis L. by activation of antioxidant defense system and accumulation of osmolytes

This study is aimed at evaluating the effects of TiO₂NPs on biochemical and physiological parameters of marigold (Calendula officinalis L.) under NaCl stress. Treatments included TiO₂NPs applied as foliar spraying in three levels (50, 100, and 200 mgL^-1), no foliar application as control, and different NaCl levels (0, 30, 60, and 90 mM) by adding NaCl to irrigation water. According to the results, the application of different concentrations of TiO₂ had various effects on the studied parameters. The use of 100 mgL^-1 TiO₂NPs increased flavonoid content of the leaves (at 30 mM NaCl), cell membrane injury (with no salinity), CAT and SOD activities (at 90 mM NaCl), and PPO activity (at 60 mM NaCl). On the other hand, using 100 mgL^-1 TiO₂NPs under salinity stress decreased MDA and H₂O₂ contents. Moreover, using 200 mgL^-1 TiO₂NPs increased photosynthetic pigments content, total flavonoid content of flowers, total soluble sugar, carotenoid content of flowers, and RWC (at the treatment with no salinity), aboveground and underground biomasses (at 30 mM and 60 mM NaCl, respectively), phenolic content and antioxidant activity (at 30 mM NaCl), and APX activity (at 90 mM NaCl). In conclusion, the findings of the present study indicated that TiO₂NPs could be a useful material to mitigate the harmful effects of salinity stress. Furthermore, the TiO₂NPs spraying could have beneficial effects on osmotic adjustment, biochemical compound, non-enzymatic and enzymatic antioxidant activities, and growth of marigold under NaCl stress conditions.

Molecular responses of legumes to abiotic stress: post-translational modifications of proteins and redox signaling

Legumes include several major crops that can fix atmospheric nitrogen in symbiotic root nodules, thus reducing the demand for nitrogen fertilizers and contributing to sustainable agriculture. Global change models predict increases in temperature and extreme weather conditions. This scenario might increase plant exposure to abiotic stresses and negatively affect crop production. Regulation of whole plant physiology and nitrogen fixation in legumes during abiotic stress is complex, and only a few mechanisms have been elucidated. Reactive oxygen species (ROS), reactive nitrogen species (RNS), and reactive sulfur species (RSS) are key players in the acclimation and stress tolerance mechanisms of plants. However, the specific redox-dependent signaling pathways are far from understood. One mechanism by which ROS, RNS, and RSS fulfil their signaling role is the post-translational modification (PTM) of proteins. Redox-based PTMs occur in the cysteine thiol group (oxidation, S-nitrosylation, S-glutathionylation, persulfidation), and also in methionine (oxidation), tyrosine (nitration), and lysine and arginine (carbonylation/glycation) residues. Unraveling PTM patterns under different types of stress and establishing the functional implications may give insight into the underlying mechanisms by which the plant and nodule respond to adverse conditions. Here, we review current knowledge on redox-based PTMs and their possible consequences in legume and nodule biology.

Biochar application modified growth and physiological parameters of Ocimum ciliatum L. and reduced human risk assessment under cadmium stress

Biochar (BC) is prepared from waste organic material that can improve soil health in the contaminated area. Soil pollution with cadmium (Cd) is one of the worldwide problems. The present study aimed to evaluate the BC influence on some morphophysiological and biochemical characteristics, also Cd concentration of Ocimum ciliatum L. leaves under Cd stress as well as human risk assessment. Therefore, a pot factorial arrangement based on a completely randomized design was done which included three levels of BC (non-BC, 1%, and 2% of the pot soil) and three Cd levels (0, 20, and 40 mg/kg soil) with three replications. The results of the present study indicated that BC application improved morphological traits, photosynthetic pigments, relative water content (RWC), and catalase (CAT) activity of O. ciliatum under Cd stress and reduced total soluble sugars, total phenol, antioxidant activity, proline content, electrolyte leakage (EL), soluble protein content, ascorbate peroxidase (APX), and guaiacol peroxidase (GPX) activities, and Cd concentration as well as target hazard quotient (THQ). In conclusion, based on the findings of this study, BC could be applied as an environmental friendly amendment in Cd-polluted soil to ameliorate the negative influences of Cd stress on O. ciliatum and reduces Cd levels and THQ in the plants due to the absorption properties of BC. This means that BC usage in contaminated soil helps to reduce pollutions and decreases the human risk assessment.

Changes in the physiological characteristics of Panax ginseng embryogenic calli and molecular mechanism of ginsenoside biosynthesis under cold stress

Short-term cold stress can induce the increased expression of key enzyme-encoding genes involved in secondary metabolite synthesis, thereby increasing secondary metabolite concentration. Cold stress is an ecologically limiting factor that strongly affects the physiological and biochemical properties of medicinal plants often resulting in changes of the secondary metabolic process. Ginsenosides are the main active ingredients in medicinal ginseng yet few studies exist on the effect of cold stress on the expression of ginsenosides or the molecular mechanism underlying its regulation. Here, we evaluated the effects of cold stress on the physiological characteristics and secondary metabolism of P. ginseng embryogenic calli. Physiological measurements and RNA-Seq analysis were used to dissect the metabolic and molecular responses of P. ginseng to cold conditions. We found that the dynamic accumulation of ginsenoside and various physiological indicators leads to homogenous adaptation to cold stress. Secondary metabolism of ginseng could be a compensation mechanism to facilitate its adaptation to cold stress. Combined with the changes in the endogenous hormone content, 9-cis-epoxycarotenoid dioxygenase (NCED), zeaxanthin epoxidase (ZEP), and short chain dehydrogenase (SDR) from the abscisic acid (ABA) synthesis pathway were identified as key mediators of this response. Thus, an appropriate degree of cold stress may promote accumulation of ginsenosides. Moreover, 3-hydroxy-3-methylglutaryl-CoA reductase (HMGR2), squalene epoxidase (SE1), squalene synthase (SS), dammarenediol synthase (DS-II), and β-alanine C-28 hydroxylase (CYP716A52v2) should be considered key mediators of the cold stress response and ginsenoside biosynthesis. During industrial production, short-term cold stress should be carried out on ginseng calli to improve the quality of its medicinal materials.

Regulation of superoxide dismutase activity in soybean plants by inoculating seeds with rhizobia containing nanoparticles of metal carboxylates under conditions of different water supply

Soybean is one of the most profitable advanced crops in agricultural production in Ukraine and the world as a whole. Therefore, studies of means of regulation and increase in the adaptive capacity of soybeans in symbiosis with nodule bacteria under the action of unfavourable environmental factors are relevant and should be aimed at the use of complex bacterial compositions involving modern nanotechnological approaches. Nanocarboxylates of ferrum, molybdenum and germanium metals were used as components of rhizobia inoculation suspension for soybean seed treatment to study the effectiveness of their complex effect on the regulation of the activity of the key antioxidant enzyme superoxide dismutase in plants under drought. Various symbiotic systems were used, which included soybean plants and inoculation suspensions based on the active, virulent Tn5-mutant Bradyrhizobium japonicum B1-20 by adding nanoparticles of ferrum, germanium and molybdenum carboxylates to the culture medium in a ratio of 1: 1000. Citric acid was the chelator. A model drought lasting 14 days was created during the period of active fixation of atmospheric molecular nitrogen by root nodules of soybeans in the budding and flowering stages, by means of controlled watering of plants to 30% of the total moisture content. In the stage of bean formation, watering of plants was resumed to the optimal level – 60% of the total moisture content. The control was soybean plants, the seeds of which were inoculated with a suspension of rhizobia without the addition of chelated metals. The following research methods were used in the work – microbiological, physiological and biochemical. According to the results, it was found that when nanoparticles of carboxylates of ferrum, molybdenum and germanium were added to the inoculation suspension of rhizobia, there was an increase in superoxide dismutase activity in root nodules and a decrease in soybean leaves under optimal water supply conditions of plants. This indicates the initial changes in the activity of the antioxidant enzyme in these symbiotic systems, induced by the influence of chelated metals in combination with the rhizobia of the active Tn5-mutant B. japonicum B1-20. Prolonged drought induced an increase in the overall level of superoxide dismutase activity in soybean nodules and leaves, compared to plants grown under optimal watering conditions. The symbiotic system formed by soybeans and B. japonicum with molybdenum carboxylate nanoparticles was the most sensitive to long-term drought exposure, compared to two other soybean-rhizobial symbioses using ferrum and germanium nanocarboxylates. This was manifested in the unstable reaction of the enzyme to the action of drought – suppression or intensification of the level of its activity in the root nodules and leaves of soybeans inoculated with rhizobia containing molybdenum carboxylate nanoparticles. In symbiotic systems with the participation of germanium and ferrum nanocarboxylates, slight changes were revealed in superoxide dismutase activity in root nodules and leaves of plants during drought and restoration of enzyme activity to the level of plants with optimal watering after water stress. It is concluded that the addition to the culture medium of rhizobia Tn5-mutant B1-20 of nanocarboxylates of germanium or ferrum is an effective means of regulating the activity of the antioxidant enzyme superoxide dismutase in soybean root nodules and leaves, which can contribute to an increase in the protective properties and adaptation of plants to the action of dehydration.

Toxicity of insecticidal proteins from entomopathogenic bacteria to Galleria mellonella larvae

Entomopathogenic bacteria have great potential in insect control in the agricultural production because they produce a large variety of protein toxins that can kill their hosts by damaging the insect midgut. However, the mechanisms on how these toxins or specific insecticidal proteins act on insects are very diverse and elusive. Here we select Galleria mellonella larvae as the host to explore the effects of insecticidal proteins on the activities of three protective enzymes (SOD, POD, and CAT) and on the morphology of the midgut tissues. As a result, the activities of the three enzymes consistently increased and then decreased when the host was injected with the insecticidal proteins from the entomopathogenic bacterium Enterobacter cloacae. Moreover, the microscopy analysis showed that tissues, cells, and organelles of the host midgut are all diseased after uptake of the insecticidal proteins. Remarkably, the protein toxins contributed to the deformation of the midgut, blackening of the midgut surface, dissolution of cell membrane, shrinkage of cell nucleus, and chromatin condensation. Our findings will advance the explanation of G. mellonella pathogenesis caused by the insecticidal proteins.

Identification of Root-Associated Bacteria That Influence Plant Physiology, Increase Seed Germination, or Promote Growth of the Christmas Tree Species Abies nordmanniana

Abies nordmanniana is used for Christmas tree production but poor seed germination and slow growth represent challenges for the growers. We addressed the plant growth promoting potential of root-associated bacteria isolated from A. nordmanniana. Laboratory screenings of a bacterial strain collection yielded several Bacillus and Paenibacillus strains that improved seed germination and produced indole-3-acetic acid. The impact of three of these strains on seed germination, plant growth and growth-related physiological parameters was then determined in greenhouse and field trials after seed inoculation, and their persistence was assessed by 16S rRNA gene-targeted bacterial community analysis. Two strains showed distinct and significant effects. Bacillus sp. s50 enhanced seed germination in the greenhouse but did not promote shoot or root growth. In accordance, this strain did not increase the level of soluble hexoses needed for plant growth but increased the level of storage carbohydrates. Moreover, strain s50 increased glutathione reductase and glutathione-S-transferase activities in the plant, which may indicate induction of systemic resistance during the early phase of plant development, as the strain showed poor persistence in the root samples (rhizosphere soil plus root tissue). Paenibacillus sp. s37 increased plant root growth, especially by inducing secondary root formation, under in greenhouse conditions, where it showed high persistence in the root samples. Under these conditions, it further it increased the level of soluble carbohydrates in shoots, and the levels of starch and non-structural carbohydrates in roots, stem and shoots. Moreover, it increased the chlorophyll level in the field trial. These findings indicate that this strain improves plant growth and vigor through effects on photosynthesis and plant carbohydrate reservoirs. The current results show that the two strains s37 and s50 could be considered for growth promotion programs of A. nordmanniana in greenhouse nurseries, and even under field conditions.

Loss of control of the culturable bacteria in the hindgut of Bombyx mori after Cry1Ab ingestion

Bt protein, produced by Bacillus thuringiensis, can bind receptors to destroy the physiological functions of the insect midgut. It is unknown whether Bt can also target the hindgut and influence its defense against fecal bacteria. Here we show that Crystal protein 1Ab (Cry1Ab), a Bt protein, was detected in the larval hindgut contents of Bombyx mori after ingestion of this toxin protein. The number of fecal bacteria that can be inhibited by the hindgut prophenoloxidase-induced melanization was significantly enhanced after oral ingestion of Cry1Ab. Although the hindgut contents became brown, the activity of hindgut phenoloxidase was decreased. LC-MS/MS analysis of the hindgut lumen contents revealed that many new proteins including several proteases were newly secreted. The enhanced secretion of proteases cleaved prophenoloxidase to decrease its activity, including the corresponding activity to inhibit the fecal bacteria. In addition, after ingestion of Cry1Ab, the pylorus (between the midgut and hindgut) could not autonomously contract due to the physical detachment of the acellular cuticle-like membrane from the epidermal cells, which prevented the movement of food from the midgut to the hindgut. Some cells in the cryptonephry of the hindgut became swollen and degraded, possibly due to the presence of Cry1Ab in the hindgut. These findings demonstrate that the inhibition of feces bacteria by the hindgut prophenoloxidase-induced melanization is out of control after Cry1Ab ingestion.

Physiological response of cucumber (Cucumis sativus L.) leaves to polystyrene nanoplastics pollution

Microplastics pollution in farmlands has become a major concern. However, few studies have assessed the effects of microplastics on higher plants. In this study, we investigated the influence of polystyrene nanoplastics (PSNPs, 50 mg L^-1), with four different particle sizes (100, 300, 500, and 700 nm), on the physiological and biochemical indexes of cucumber leaves. The biomass of cucumber plants significantly decreased after exposure to 300 nm PSNPs. Similarly, the chlorophyll a, chlorophyll b, soluble sugar, carotenoid, and proline content, as well as the fluorescence of cucumber leaves were significantly reduced by 100 nm PSNPs. Malondialdehyde, proline, peroxidase gene expression and enzyme activity, and hydrogen peroxide content significantly increased in cucumber leaves exposed to 700 nm PSNPs. In addition, increasing PSNPs particle size led to decreased relative expression levels and activities of the major antioxidant enzymes superoxide dismutase and catalase, while vitamin C and soluble protein content significantly increased. Overall, our results indicated that PSNPs affect the photosynthetic, antioxidant, and sugar metabolism systems of cucumber leaves, with the latter clearly affecting the total biomass of cucumber plants. The benzene ring resulting from the degradation of PSNPs in cucumber leaves may be the main factor affecting chlorophyll metabolism and sugar metabolism. Our findings provide a scientific basis for the risk assessment of PSNPs exposure in soil-plant systems.

Penconazole and calcium ameliorate drought stress in canola by upregulating the antioxidative enzymes

The aim of this research was to gauge the alternations in the lipid peroxidation and antioxidative enzyme activity in two cultivars (cv. RGS003 and cv. Sarigol) of canola under drought stress and drought tolerance amelioration by penconazole (PEN) and calcium (Ca). Plants were treated with different polyethylene glycol (PEG) concentrations (0, 5, 10 and 15%) without or with PEN (15 mg L-1) and Ca (15 mM). The Ca treatment prevented the negative effects of drought on fresh weight (FW) in RGS003 and Sarigol at 5 and 15% PEG respectively. Ca and PEN/Ca treatments caused significant induction in the proline content in Sarigol at 15% PEG; the latter treatment was accompanied by higher glycine betaine (GB), lower malondialdehyde (MDA) and growth recovery. Hydrogen peroxide (HO2) content in Sarigol was proportional to the severity of drought stress and all PEN, Ca and PEN/Ca treatments significantly reduced the H2O2 content. PEN and PEN/Ca caused alleviation of the drought-induced oxidative stress in RGS003. RGS003 cultivar exhibited significantly higher antioxidative enzymes activity at most levels of drought, which could lead to its drought tolerance and lower MDA content. In contrast to that of Sarigol, the activity of catalase and superoxide dismutase (SOD) increased with Ca and PEN/Ca treatments in RGS003 under low stress. The application of PEN and Ca induced significantly P5CS and SOD expression in RGS003 under drought stress after 24 h. Overall, these data demonstrated that PEN and Ca have the ability to enhance the tolerance against the drought stress in canola plants.

Foliar application of melatonin delay leaf senescence in maize by improving the antioxidant defense system and enhancing photosynthetic capacity under semi-arid regions

Melatonin is an important plant growth regulator which plays a key role in plant growth and development. The objective of the current research was to evaluate the effect of foliar application of melatonin (MF) on photosynthetic efficiency, antioxidant defense mechanism, and its relation with leaf senescence in maize crop grown in a semi-arid region. A field experiment was conducted during 2017 and 2018 growth season, where melatonin was applied to the foliage at concentrations of 0 (MF₀), 25 (MF₁), 50 (MF₂), and 75 (MF₃) μM at the ninth leaf stage. Foliar application of melatonin significantly improved chlorophyll content, net photosynthetic rate, soluble sugar content, and soluble protein content during the process of leaf senescence. The application of melatonin also enhanced antioxidant enzyme activities including superoxide dismutase, catalase, and peroxidase, while reduced malondialdehyde and reactive oxygen species accumulation. Melatonin foliar application also increased total leaf area per plant, grains per ear, thousand grain weight and grain yield of maize crop in a semi-arid region. The application of melatonin significantly improved photosynthetic activity, antioxidant defense mechanism, and yield of maize crop in a semi-arid region, where the most effective treatment was MF2.

Ursolic Acid Limits Salt-Induced Oxidative Damage by Interfering With Nitric Oxide Production and Oxidative Defense Machinery in Rice

Crops frequently encounter abiotic stresses, and salinity is a prime factor that suppresses plant growth and crop productivity, globally. Ursolic acid (UA) is a potential signaling molecule that alters physiology and biochemical processes and activates the defense mechanism in numerous animal models; however, effects of UA in plants under stress conditions and the underlying mechanism of stress alleviation have not been explored yet. This study examined the effects of foliar application of UA (100 μM) to mitigate salt stress in three rice cultivars (HZ, 712, and HAY). A pot experiment was conducted in a climate-controlled greenhouse with different salt stress treatments. The results indicated that exposure to NaCl-induced salinity reduces growth of rice cultivars by damaging chlorophyll pigment and chloroplast, particularly at a higher stress level. Application of UA alleviated adverse effects of salinity by suppressing oxidative stress (H2O2, O2-) and stimulating activities of enzymatic and non-enzymatic antioxidants (APX, CAT, POD, GR, GSH, AsA, proline, glycinebutane), as well as protecting cell membrane integrity (MDA, LOX, EL). Furthermore, UA application brought about a significant increase in the concentration of leaf nitric oxide (NO) by modulating the expression of NR and NOS enzymes. It seems that UA application also influenced Na+ efflux and maintained a lower cytosolic Na+/K+ ratio via concomitant upregulation of OsSOS1 and OsHKT1;5 in rice cultivars. The results of pharmacological tests have shown that supply of the NO scavenger (PTI) completely reversed the UA-induced salt tolerance in rice cultivars by quenching endogenous NO and triggering oxidative stress, Na+ uptake, and lipid peroxidation. The PTI application with UA and sodium nitroprusside (SNP) also caused growth retardation and a significant increase in Na+ uptake and oxidative stress in rice cultivars. This suggests that UA promoted salt tolerance of rice cultivars by triggering NO production and limiting toxic ion and reactive oxygen species (ROS) accumulation. These results revealed that both UA and NO are together required to develop a salt tolerance response in rice.

Assessment of changes in growth traits, oxidative stress parameters, and enzymatic and non-enzymatic antioxidant defense mechanisms in Lepidium draba plant under osmotic stress induced by polyethylene glycol

Lepidium draba is a weed with the medicinal properties which few researches have been done on it. In this study, some traits, related to the osmotic stress, in 14-day-old L. draba sprouts that were grown 9 days in the presence of various doses of polyethylene glycol 6000 (PEG 6000) including 0, 3, 6, 9, and 12%, with different osmotic potentials (- 0.04, - 0.12, - 0.23, - 0.34, and - 0.48 MPa, respectively) were investigated. Based on our results, germination percentage besides stem and root lengths decreased with increasing the concentrations of PEG. The contents of electrolyte leakage, malondialdehyde, other aldehydes, total protein, free amino acids, total soluble carbohydrate as well as free proline increased with increasing the concentrations of PEG. Also, for the first time, our results have proven that under osmotic stress, there is an adverse relationship between hydrogen peroxide content and the activity of catalase, peroxidase, ascorbate peroxidase, and guaiacol peroxidase enzymes, such that hydrogen peroxide content decreased with induction of PEG up to 6% and after that increased, while the activity of catalase, peroxidase, ascorbate peroxidase, and guaiacol peroxidase enzymes increased up to 6% PEG and after that decreased. The expression levels of catalase, peroxidase, ascorbate peroxidase, and guaiacol peroxidase genes showed the same pattern as was seen for these enzyme activities. According to the results of this study, it can be deduced that decreasing H₂O₂ content cannot be the main reason for other oxidative stress parameters to decrease. In this study, P5CS and P5CR gene expression levels increased with increasing levels of PEG up to 12% which was completely similar to free proline content. Based on our results, L. draba can be considered as a semi-tolerant plant to osmotic stress.

Identification of Root-Associated Bacteria That Influence Plant Physiology, Increase Seed Germination, or Promote Growth of the Christmas Tree Species Abies nordmanniana

Abies nordmanniana is used for Christmas tree production but poor seed germination and slow growth represent challenges for the growers. We addressed the plant growth promoting potential of root-associated bacteria isolated from A. nordmanniana. Laboratory screenings of a bacterial strain collection yielded several Bacillus and Paenibacillus strains that improved seed germination and produced indole-3-acetic acid. The impact of three of these strains on seed germination, plant growth and growth-related physiological parameters was then determined in greenhouse and field trials after seed inoculation, and their persistence was assessed by 16S rRNA gene-targeted bacterial community analysis. Two strains showed distinct and significant effects. Bacillus sp. s50 enhanced seed germination in the greenhouse but did not promote shoot or root growth. In accordance, this strain did not increase the level of soluble hexoses needed for plant growth but increased the level of storage carbohydrates. Moreover, strain s50 increased glutathione reductase and glutathione-S-transferase activities in the plant, which may indicate induction of systemic resistance during the early phase of plant development, as the strain showed poor persistence in the root samples (rhizosphere soil plus root tissue). Paenibacillus sp. s37 increased plant root growth, especially by inducing secondary root formation, under in greenhouse conditions, where it showed high persistence in the root samples. Under these conditions, it further it increased the level of soluble carbohydrates in shoots, and the levels of starch and non-structural carbohydrates in roots, stem and shoots. Moreover, it increased the chlorophyll level in the field trial. These findings indicate that this strain improves plant growth and vigor through effects on photosynthesis and plant carbohydrate reservoirs. The current results show that the two strains s37 and s50 could be considered for growth promotion programs of A. nordmanniana in greenhouse nurseries, and even under field conditions.

Dynamic trajectories of volatile and non-volatile specialised metabolites in 'overnight' fragrant flowers of Murraya paniculata

Ephemeral flowers, especially nocturnal ones, usually emit characteristic scent profiles within their post-anthesis lifespans of a few hours. Whether these flowers exhibit temporal variability in the composition and profile of volatile and non-volatile specialised metabolites has received little attention. Flowers of Murraya paniculata bloom in the evenings during the summer and monsoon, and their sweet, intense fragrance enhances the plant's value as an ornamental. We aimed to investigate profiles of both volatile and non-volatile endogenous specialised metabolites (ESM) in nocturnal ephemeral flowers of M. paniculata to examine whether any biochemically diverse groups of ESM follow distinct patterns of accumulation while maintaining synchrony with defensive physiological functions. Targeted ESM contents of M. paniculata flowers were profiled at ten time points at 2-h intervals, starting from late bud stage (afternoon) up to the start of petal senescence (mid-morning). Emitted volatiles were monitored continuously within the whole 20-h period using headspace sampling. The ESM contents were mapped by time point to obtain a highly dynamic and biochemically diverse profile. Relative temporal patterns of ESM accumulation indicated that the active fragrance-emitting period might be divided into 'early bloom', 'mid-bloom' and 'late bloom' phases. Early and late bloom phases were characterised by high free radical generation, with immediate enhancement of antioxidant enzymes and phenolic compounds. The mid-bloom phase was relatively stable and dedicated to maximum fragrance emission, with provision for strong terpenoid-mediated defence against herbivores. The late bloom phase merged into senescence with the start of daylight; however, even the senescent petals continued to emit fragrance to attract diurnal pollinators. Our study suggests that dynamic relations between the different ESM groups regulate the short-term requirements of floral advertisement and phytochemical defence in this ephemeral flower. This study also provided fundamental information on the temporal occurrence of emitted volatiles and internal pools of specialised metabolites in M. paniculata flowers, which could serve as an important model for pollination biology of Rutaceae, which includes many important fruit crops.

Root-Associated Microbial Communities of Abies nordmanniana: Insights Into Interactions of Microbial Communities With Antioxidative Enzymes and Plant Growth

Abies nordmanniana is a major Christmas tree species in Europe, but their uneven and prolonged growth slows down their production. By a 16S and 18S rRNA gene amplicon sequencing approach, we performed a characterization of root-associated bacterial and fungal communities for three-year-old A. nordmanniana plants collected from two nurseries in Denmark and Germany and displaying different growth patterns (small versus tall plants). Proteobacteria had the highest relative abundance at both sampling sites and plant sizes, and Ascomycota was the most abundant fungal phylum. At the order level, Acidobacteriales, Actinomycetales, Burkholderiales, Rhizobiales, and Xanthomonadales represented the bacterial core microbiome of A. nordmanniana, independently of the sampling site or plant size, while the fungal core microbiome included members of the Agaricales, Hypocreales, and Pezizales. Principal Coordinate Analysis indicated that both bacterial and fungal communities clustered according to the sampling site pointing to the significance of soil characteristics and climatic conditions for the composition of root-associated microbial communities. Major differences between communities from tall and small plants were a dominance of the potential pathogen Fusarium (Hypocreales) in the small plants from Germany, while Agaricales, that includes reported beneficial ectomycorrhizal fungi, dominated in the tall plants. An evaluation of plant root antioxidative enzyme profiles showed higher levels of the antioxidative enzymes ascorbate peroxidase, peroxidase, and superoxide dismutase in small plants compared to tall plants. We suggest that the higher antioxidative enzyme activities combined with the growth arrest phenotype indicate higher oxidative stress levels in the small plants. Additionally, the correlations between the relative abundances of specific taxa of the microbiome with the plant antioxidative enzyme profiles were established. The main result was that many more bacterial taxa correlated positively than negatively with one or more antioxidative enzyme activity. This may suggest that the ability of bacteria to increase plant antioxidative enzyme defenses is widespread.

Guaiacol oxidation activity of herbivorous land crabs, Chiromantes haematocheir and Chiromantes dehaani

The land crabs, Chiromantes haematocheir (Akate-gani) and Chiromantes dehaani (Kurobenkei-gani) inhabit seaside forests in Japan. The crabs mainly consume plant material and its detritus. Therefore, they are expected to possess the ability to degrade the major components of biomass, cellulose and lignin in order to digest plant materials. In this study, we analyzed biomass-degrading activities of the land crabs, especially guaiacol oxidation activity, which seems to be related to lignin degradation. Cellulase activity was detected from almost all gut samples including the stomach, midgut gland and intestine of all dissected crabs. Conversely, high guaiacol oxidation activity was detected in the midgut gland of all C. dehaani and several female C. haematocheir crabs. This is consistent with a previous study showing that female crabs were more herbivorous than male crabs were and observation that C. dehaani crabs are more herbivorous than C. haematocheir. Guaiacol oxidation activity might play an important role in the herbivorous behavior of land crabs.

Leptolyngbya fragilis ISC 108 is the most effective strain for dodecane biodegradation in contaminated soils

One of the major environmental problems nowadays is petroleum hydrocarbons contamination. Bioremediation is widely used for cleaning ecosystems contaminated with petroleum hydrocarbons. This study was carried out to investigate the response of five microalgae strains isolated from different regions in Iran for 1% n-dodecane (DOD) degradation. The results revealed that Leptolyngbya fragilis ISC 108 is the most effective strain to utilize n-DOD as growth substrate under a mixotrophic condition. Currently, there is little information about mechanisms involved in microalgae response against DOD. The activity of antioxidant enzymes and total lipid and carbohydrate contents were observed to be greater in DOD-treated L. fragilis ISC 108. Lower values of lipid peroxidation and H₂O₂ along with an increase of dry weight and specific growth rate in L. fragilis ISC 108 under DOD treatment shows that at the cellular level this strain is better equipped with an efficient oxygen radical scavenging system. In conclusion, this study proposes that L. fragilis ISC 108 can be considered an ideal candidate for use in bioremediation of DOD contaminated sites.

Gracilaria dura extract confers drought tolerance in wheat by modulating abscisic acid homeostasis

Water stress severely reduces the production of wheat. Application of seaweed extracts have started to show promise in protecting plants from environmental stresses as they contain several biostimulants. However, the modes of action of these biostimulants are not clear. Here, we investigated the role of Gracilaria dura (GD), a red alga, in conferring stress tolerance to wheat during drought under glasshouse and agro-ecological conditions by integrating molecular studies with physiological and field investigations. GD-sap application conferred drought tolerance (as the biomass increased by up to 57% and crop yield by 70%), via facilitating physiological changes associated to maintaining higher water content. GD-sap application significantly increased ABA accumulation (2.34 and 1.46 fold at 4 and 6 days of drought, respectively) due to enhanced expression of biosynthesis genes. This followed an activation of ABA response genes and physiological processes including reduced stomatal opening, thus reducing water loss. Moreover, GD-sap application enhanced the expression of stress-protective genes specifically under water stress. Treatment with fluridone, an ABA inhibitor, further support the role of ABA in GD-sap mediated drought tolerance in wheat. The findings of this study provide insights into the functional role of GD-sap in improving drought tolerance and show the potential to commercialize GD-sap as a potent biostimulant for sustainable agriculture in regions prone to drought.

L-DOPA Trends in Different Tissues at Early Stages of Vicia faba Growth: Effect of Tyrosine Treatment

The nonprotein amino acid Levo-3,4-dihydroxyphenylalanine (L-DOPA) has insecticidal, allelochemical, and antiparkinsonian effects. The aim of this research was to assess L-DOPA content in different tissues of Vicia faba (cv. Super Agua Dulce), and to verify if treatment with the phenolic amino acid L-4-hydroxyphenylalanine (tyrosine) had an effect on such content. Under light germination, control and tyrosine-treated early seedling stages of V. faba were studied and L-DOPA was quantified spectrophotometrically (Arnow’s method) and by high-performance thin-layer chromatography (HPTLC), as well. Additionally, tyrosinase (TYROX) and guaiacol peroxidase (GPX) activities (considered markers of a phenolic compounds metabolism) were quantified as germination proceeded. Different organs (roots, sprouts, and seeds) and different developmental stages were considered. Steady high L-DOPA concentrations were found in untreated sprouts and roots compared to seeds, as time progressed. While TYROX activity was not detected in these experiments, GPX had diverse trends. In control tissues, GPX increased in seed tissue as germination progressed, whereas in roots and sprouts, a decreasing GPX activity was observed. Tyrosine exposure decreased L-DOPA content, and decreased or did not change GPX activity (depending on the organ). Both Arnow’s and HPTLC methods were consistent in terms of tendencies, except for the scarce contents found in seeds, in which HPTLC was more sensitive. The richest source of L-DOPA was found in shoots (untreated), reaching as high as 125 mg g−1 DW (12% in DW) (the highest content reported in fava bean seedlings until now), whereas the smallest L-DOPA content was found in seeds. The importance of light germination conditions is discussed in terms of L-DOPA yield and from a physiological perspective. It is concluded that V. faba (cv. Super Agua Dulce) shoots are a good source of L-DOPA and that tyrosine addition (0.55 mM) decreases L-DOPA content in actively growing tissues (shoots and roots).