Comparative effect of 28-homobrassinolide and 24-epibrassinolide on the performance of different components influencing the photosynthetic machinery in Brassica juncea L

Preliminary Treatment by Exogenous 24-Epibrassinolide Influences Burning-Induced Electrical Signals and Following Photosynthetic Responses in Pea (Pisum sativum L.)

Long-distance electrical signals (ESs) are an important mechanism of induction of systemic adaptive changes in plants under local action of stressors. ES-induced changes in photosynthesis and transpiration play a key role in these responses increasing plant tolerance to action of adverse factors. As a result, investigating ways of regulating electrical signaling and ES-induced physiological responses is a perspective problem of plant electrophysiology. The current work was devoted to the analysis of the influence of preliminary treatment (spraying) by exogenous 24-epibrassinolide (EBL) on burning-induced ESs and following photosynthetic and transpiratory responses in pea (Pisum sativum L.). It was shown that preliminary treatment by 1 µM EBL (1 day before the experiment) increased the amplitude of burning-induced ESs (variation potentials) in leaves and decreased the time of propagation of these signals from the stem to the leaf. The EBL treatment weakly influenced the magnitudes of burning-induced decreasing the photosynthetic linear electron flow and CO2 assimilation, but these changes were accelerated. Burning-induced changes in the cyclic electron flow around photosystem I were also affected by the EBL treatment. The influence of the EBL treatment on burning-induced changes in the stomatal water conductance was not observed. Our results show that preliminary treatment by EBL can be used for the modification of electrical signals and following photosynthetic responses in plants.

Application of waste eggshells elevates phytoremediation efficiency of Pb-Zn mine-contaminated farmland and mitigates soil greenhouse gas emissions: A field study

Remediating heavy metal (HM)-contaminated farmlands and sequestering soil carbon for emission reduction have been prominent topics in environmental research in recent years. However, few studies have looked into the soil greenhouse gas (GHG) impacts of growing hyperaccumulators in composite HM-contaminated farmland, as well as agronomic measures to remediate soil HMs while mitigating GHG emissions. To investigate fertilization measures to improve phytoremediation efficiency and mitigate GHG emissions, S. photeinocarpum was planted with three different fertilization measures on farmland contaminated by lead-zinc (Pb-Zn) mines (1200 kg ha-1 eggshell, 125 kg ha-1 28-homobrassinolide, and 16.7 kg ha-1 mineral potassium fulvic acid) during its growth period. The findings are as follows: Eggshell application significantly enhanced the translocation factor (TF) of Pb, Zn, and cadmium (Cd) from the roots to the shoots of Solanum photeinocarpum. Moreover, eggshells notably increased the bioaccumulation factor (BCF) of Cd and Pb in plant shoots by 120.75% and 159.09%, respectively. Regarding GHG emissions, the combined application of eggshells and 28-homobrassinolide substantially lowered the global warming potential (GWP) of the soil. Correlation analyses revealed that eggshell application increased the relative abundance of the Gemmatimonadota bacterial phylum in the soil, facilitating Pb and Cd migration from the roots to shoot tissues in S. photeinocarpum. Eggshell use inhibited nitrate nitrogen (NO3--N) transformation into nitrous oxide (N2O) by the Myxococcota bacterial phylum and reduced N2O release from the soil. The application of low-cost eggshells can achieve a win-win situation of soil HM remediation and GHG emission reduction, as well as provide simple and scalable management measures for HM-contaminated farmland.

Deciphering the Mechanism of Melatonin-Induced Enhancement of Photosystem II Function in Moderate Drought-Stressed Oregano Plants

Melatonin (MT) is considered as an antistress molecule that plays a constructive role in the acclimation of plants to both biotic and abiotic stress conditions. In the present study, we assessed the impact of 10 and 100 μM MT foliar spray, on chlorophyll content, and photosystem II (PSII) function, under moderate drought stress, on oregano (Origanum vulgare L.) plants. Our aim was to elucidate the molecular mechanism of MT action on the photosynthetic electron transport process. Foliar spray with 100 μM MT was more effective in mitigating the negative impact of moderate drought stress on PSII function, compared to 10 μM MT. MT foliar spray significantly improved the reduced efficiency of the oxygen-evolving complex (OEC), and PSII photoinhibition (Fv/Fm), which were caused by drought stress. Under moderate drought stress, foliar spray with 100 μM MT, compared with the water sprayed (WA) leaves, increased the non-photochemical quenching (NPQ) by 31%, at the growth irradiance (GI, 205 μmol photons m-2 s-1), and by 13% at a high irradiance (HI, 1000 μmol photons m-2 s-1). However, the lower NPQ increase at HI was demonstrated to be more effective in decreasing the singlet-excited oxygen (1O2) production at HI (-38%), in drought-stressed oregano plants sprayed with 100 μM MT, than the corresponding decrease in 1O2 production at the GI (-20%), both compared with the respective WA-sprayed leaves under moderate drought. The reduced 1O2 production resulted in a significant increase in the quantum yield of PSII photochemistry (ΦPSII), and the electron transport rate (ETR), in moderate drought-stressed plants sprayed with 100 μM MT, compared with WA-sprayed plants, but only at the HI (+27%). Our results suggest that the enhancement of PSII functionality, with 100 μM MT under moderate drought stress, was initiated by the NPQ mechanism, which decreased the 1O2 production and increased the fraction of open PSII reaction centers (qp), resulting in an increased ETR.

Integrated physiological, transcriptomic, and metabolomic analyses of drought stress alleviation in Ehretia macrophylla Wall. seedlings by SiO2 NPs (silica nanoparticles)

With environmental problems such as climate global warming, drought has become one of the major stress factors, because it severely affects the plant growth and development. Silicon dioxide nanoparticles (SiO2 NPs) are crucial for mitigating abiotic stresses suffered by plants in unfavorable environmental conditions and further promoting plant growth, such as drought. This study aimed to investigate the effect of different concentrations of SiO2 NPs on the growth of the Ehretia macrophylla Wall. seedlings under severe drought stress (water content in soil, 30-35%). The treatment was started by starting spraying different concentrations of SiO2 NPs on seedlings of Ehretia macrophyla, which were consistently under normal and severe drought conditions (soil moisture content 30-35%), respectively, at the seedling stage, followed by physiological and biochemical measurements, transcriptomics and metabolomics analyses. SiO2 NPs (100 mg·L-1) treatment reduced malondialdehyde and hydrogen peroxide content and enhanced the activity of antioxidant enzymes under drought stress. Transcriptomic analysis showed that 1451 differentially expressed genes (DEGs) in the leaves of E. macrophylla seedlings were regulated by SiO2 NPs under drought stress, and these genes mainly participate in auxin signal transduction and mitogen-activated protein kinase signaling pathways. This study also found that the metabolism of fatty acids and α-linolenic acids may play a key role in the enhancement of drought tolerance in SiO2 NP-treated E. macrophylla seedlings. Metabolomics studies indicated that the accumulation level of secondary metabolites related to drought tolerance was higher after SiO2 NPs treatment. This study revealed insights into the physiological mechanisms induced by SiO2 NPs for enhancing the drought tolerance of plants.

SlSERK3B Promotes Tomato Seedling Growth and Development by Regulating Photosynthetic Capacity

Brassinosteroids (BRs) are a group of polyhydroxylated steroids for plant growth and development, regulating numerous physiological and biochemical processes and participating in multi-pathway signaling in plants. 24-Epibrassinolide (EBR) is the most commonly used BR for the investigation of the effects of exogenous steroidal phytohormones on plant physiology. Although SlSERK3B is considered a gene involved in the brassinosteroid (BR) signaling pathway, its specific role in plant growth and development has not been reported in detail. In this study, tomato (Solanum lycopersicum L.) seedlings treated with 0.05 μmol L-1 EBR showed a significant increase in plant height, stem diameter, and fresh weight, demonstrating that BR promotes the growth of tomato seedlings. EBR treatment increased the expression of the BR receptor gene SlBRI1, the co-receptor gene SlSERK3A and its homologs SlSERK3B, and SlBZR1. The SlSERK3B gene was silenced by TRV-mediated virus-induced gene silencing (VIGS) technology. The results showed that both brassinolide (BL) content and BR synthesis genes were significantly up-regulated in TRV-SlSERK3B-infected seedlings compared to the control seedlings. In contrast, plant height, stem diameter, fresh weight, leaf area and total root length were significantly reduced in silenced plants. These results suggest that silencing SlSERK3B may affect BR synthesis and signaling, thereby affecting the growth of tomato seedlings. Furthermore, the photosynthetic capacity of TRV-SlSERK3B-infected tomato seedlings was reduced, accompanied by decreased photosynthetic pigment content chlorophyll fluorescence, and photosynthesis parameters. The expression levels of chlorophyll-degrading genes were significantly up-regulated, and carotenoid-synthesising genes were significantly down-regulated in TRV-SlSERK3B-infected seedlings. In conclusion, silencing of SlSERK3B inhibited BR signaling and reduced photosynthesis in tomato seedlings, and this correlation suggests that SlSERK3B may be related to BR signaling and photosynthesis enhancement.

Quercetin-mediated alteration in photosynthetic efficiency, sugar metabolism, elemental status, yield, and redox potential in two varieties of okra

Quercetin is a bioactive natural compound with an antioxidative property that can potentially modify plant physiology. The current investigation aimed to gauge the effect of different concentrations of foliar spray of quercetin (0, 0.5, 1, 1.5, 2.0 mM) on several morphological and physio-biochemical performances of Abelmoschus esculentus L. (Moench.) plants under normal environmental conditions. The foliar spray on the plant leaves was applied 25 days after sowing (DAS) and continued up to 30 DAS once each day. The plants were sampled at 30 and 45 DAS to monitor several parameters. The foliar treatments of quercetin significantly upgraded all the studied parameters. The results direct that most of the traits such as growth, nutrient uptake, photosynthetic, and enzyme activities were promoted in a dose-dependent way. Quercetin application lowered the reactive oxygen species (ROS) buildup by increasing the antioxidant enzyme activities. Microscopic investigations further revealed a significant enhancement in the stomatal aperture under quercetin application. Out of several doses tested, 1 mM of quercetin proved best and can be used for further investigations.

Exogenous Application of 24-Epibrassinolide Confers Saline Stress and Improves Photosynthetic Capacity, Antioxidant Defense, Mineral Uptake, and Yield in Maize

Salinity is one of the major environmental stresses threatening crop production, the natural ecosystem, global food security, and the socioeconomic health of humans. Thus, the development of eco-friendly strategies to mitigate saline stress and/or enhance crop tolerance is an important issue worldwide. Therefore, this study was conducted during the summer of 2022 to investigate the potential of 24-Epibrassinolide (EBL) for mitigating saline stress and improving photosynthetic capacity, antioxidant defense systems, mineral uptake, and yield in maize (Zea mays L.) grown under a controlled hydroponic system. Three saline stress levels-S1 (control/no added NaCl), S2 (60 mM NaCl), and S3 (120 mM NaCl)-were continuously applied with nutrient solution, whereas exogenous EBL (i.e., control, 0.1 µM and 0.2 µM) was applied as exogenous application three times (i.e., 40, 55, 70 days after sowing). The experiment was designed as a split-plot in a randomized complete block design (RCBD) in which saline stress was the main factor and EBL treatment was the sub-factor. Results showed that saline stress significantly affected plant growth, physiological performance, biochemistry, antioxidant activity, and yield attributes. However, the exogenous application of EBL at 0.2 µM significantly mitigated the salt stress and thus improved plant performance even under 120 mM NaCl saline stress. For instance, as compared to untreated plants (control), 0.2 µM EBL application improved plant height (+18%), biomass (+19%), SPAD (+32%), Fv/Fm (+28%), rate of photosynthesis (+11%), carboxylation efficiency (+6%), superoxide dismutase (SOD +14%), catalase (CAT +18%), ascorbate peroxidase (APX +20%), K+ (+24%), 100-grain weight (+11%), and grain yield (+47%) of maize grown under salt stress. Additionally, it resulted in a 23% reduction in Na+ accumulation in leaves and a 25% reduction in for Na+/K+ ratio under saline stress as compared to control. Furthermore, the Pearson's correlation and principal component analysis (PCA) highlighted the significance of exogenous EBL as saline stress mitigator in maize. Overall, our results indicated the protective effects of EBL application to the alleviation of saline stress in crop plants. However, further exploration of its mechanism of action and crop-specific response is suggested prior to commercial use in agriculture.

Insights into salicylic acid-mediated redox homeostasis, carbohydrate metabolism and secondary metabolite involvement in improvement of photosynthetic performance, enzyme activities, ionomics, and yield in different varieties of Abelmoschus esculentus

Salicylic acid (SA) is a well-known signaling molecule and phenolic plant hormone. However, the optimal concentration of SA required for beneficial effects may vary across different plant species. The objective of this study was to investigate the effects of salicylic acid (SA) on two different varieties of Abelmoschus esculentus (Sakata-713 and Neelam) in order to determine the optimal concentration of SA and its impact on the growth, physiology, and biochemical processes of the plants. We conducted an experiment applying different SA concentrations (0, 10-4, 10-5, 10-6, 10-7 M) at 25 days after sowing (DAS) and evaluated various plant parameters at different stages. To evaluate various parameters sampling was performed at 30 and 45 DAS; yield traits were calculated at 60 DAS. The results indicate that SA application increased cell division, trichome number, chlorophyll content, photosynthesis, gas exchange traits, and elemental status which further boosted plants growth and yield traits. SA application stimulated activity of several enzymes that participate in carboxylation/decarboxylation homeostasis (carbonic anhydrase), nitrogen metabolism (nitrate reductase), Calvin cycle (Rubisco), TCA cycle (succinate dehydrogenase and fumarase) and secondary metabolism (phenylalanine lyase). A gradual increase in the production of secondary metabolites (total phenol, total flavonoid, anthocyanin) and carbon metabolism (total reducing sugars, starch, glucose, fructose, sucrose) was observed. Notably, SA treatment also played a vital role in maintaining a balanced equilibrium between reactive oxygen species (ROS) and the scavenging system (catalase, peroxidase, superoxide dismutase). Based on our results, the optimal concentration of SA was determined to be 10-5 M, as it yielded the most favourable outcomes among the different concentrations tested. Moreover, when comparing the two varieties of okra, Sakata-713 exhibited a more promising response to SA treatment compared to Neelam.

24-Epibrassinolide alleviates drought effects in young Carapa guianensis plants, improving the hydraulic safety margin, gas exchange and antioxidant defence

Climate change is increasing the frequency of extreme events such as droughts, limiting plant growth and productivity. Exogenous application of plant growth regulators, such as 24-epibrassinolide (EBR), might be a solution as this molecule is organic, eco-friendly, and biodegradable. This is the first research to examine possible roles of EBR on the hydraulic safety margin, physiological behaviour, and metabolism in Carapa guianensis Aubl. (Meliaceae) exposed to drought. C. guianensis is a widely distributed tree in tropical forests of the Amazon. The objective was to determine whether EBR can improve tolerance to water deficit in young C. guianensis by measuring hydraulic traits, nutritional, biochemical and physiological responses, and biomass. The experiment had four randomized treatments: two water conditions (control and water deficit) and two concentrations of EBR (0 and 100 nM EBR). EBR increased the water potential and hydraulic safety margin, increased CO2 fixation, and improved stomatal performance. EBR also stimulated antioxidant defences (SOD, CAT, APX, and POX). Overall, tretreatment with EBR improved drought tolerance of young C. guianensis plants.

Exogenous epibrassinolide application improves essential oil biosynthesis and trichome development in peppermint via modulating growth and physicochemical processes

Peppermint has gained a promising status due to the presence of a high proportion of bioactive compounds, especially menthol. Due to its pharmacological efficacy, the demand for its plant-based bioactive compounds necessitates its cultivation worldwide. Brassinosteroids are polyhydroxylated sterol derivatives that regulate diverse processes and control many agronomic traits during plant growth and development. A factorial randomised pot experiment was performed in the net house to investigate the effect of 24-Epibrassinolide (EBL) on the growth, physiology, essential oil content, stomatal behaviour and trichome development of the three cultivars of peppermint. Four levels of foliage-applied EBL, viz. 0, 10-5, 10-6 and 10-7 M were applied to the three cultivars of peppermint (Kukrail, Pranjal and Tushar). Among the different treatments of EBL, the application of 10-6 M increased shoot length by 38.84, 37.59 and 36.91%, root length by 36.73, 29.44 and 33.47%, chlorophyll content by 24.20, 22.48 and 23.32%, PN by 32.88, 32.61 and 33.61%, EO content by 32.72, 30.00 and 28.84%, EO yield per plant by 66.66, 77.77 and 73.33% and menthol yield per plant by 127.27, 110 and 118.18% in Kukrail, Tushar and Pranjal respectively, compared with their respective control plants. Further, the 10-6 M EBL exhibited improved trichome size and density, cellular viability and menthol content of the oil analysed from scanning electron microscopy, confocal laser scanning microscopy and GC-MS respectively as compared to the control. In conclusion, out of different levels of EBL, two sprays of 10-6 M EBL proved effective in enhancing the morphophysiological features and productivity of mint plants, particularly for cultivar Kukrail.

Coal fly ash application as an eco-friendly approach for modulating the growth, yield, and biochemical constituents of Withania somnifera L. plants

The solid waste known as fly ash, which is produced when coal is burned in thermal power plants, is sustainably used in agriculture. It is an excellent soil supplement for plant growth and development since it contains some desired nutrients (macro and micro), as well as being porous. The present study was done to evaluate the effect of different fly ash levels on Withania somnifera. The present study aimed to assess the impact of various fly ash (FA) concentrations on growth, yield, photosynthetic pigments, biochemical parameters, and cell viability of W. somnifera. The results showed that FA enhanced physical and chemical properties of soil like pH, electric conductivity, porosity, water-holding capacity, and nutrients. The low doses of FA-amended soil (15%) significantly increased the shoot length (36%), root length (24.5%), fresh weight of shoots and roots (107.8 and 50.6%), dry weight of shoots and roots (61.9 and 47.1%), number of fruits (70.4%), carotenoid (43%), total chlorophyll (44.3%), relative water content (109.3%), protein content (20.4%), proline content (110.3%), total phenols (116.1%), nitrogen (20.3%), phosphorus (16.9%), and potassium (26.4%). On the other hand, the higher doses, i.e., 25% of fly ash showed a negative effect on all the above parameters and induced oxidative stress by increasing lipid peroxidation (33.1%) and hydrogen peroxide (102.0%) and improving the activities of antioxidant enzymes and osmolytes. Compared to the control plants, the plants growing in soil enriched with 15 and 25% fly ash had larger stomata pores when examined using a scanning electron microscope. In addition, according to a confocal microscopic analysis of the roots of W. somnifera, higher fly ash concentrations caused membrane damage, as evidenced by an increase in the number of stained nuclei. Moreover, several functional groups and peaks of the biomolecules represented in the control and 15% of fly ash were alcohols, phenols, allenes, ketenes, isocynates, and hydrocarbons. Gas chromatography-mass spectrometry analysis of the methanol extract of W. somnifera leaves cultivated in soil amended with 15% fly ash shows the presence of 47 bioactive compounds. The most abundant compounds in the methanol extract were cis-9-hexadecenal (22.33%), n-hexadecanoic acid (9.68%), cinnamic acid (6.37%), glycidyl oleate (3.88%), nonanoic acid (3.48%), and pyranone (3.57%). The lower concentrations of FA (15%) can be used to enhance plant growth and lower the accumulation of FA that results in environmental pollution.

Epi-Brassinolide Regulates ZmC4 NADP-ME Expression through the Transcription Factors ZmbHLH157 and ZmNF-YC2

Maize is a main food and feed crop with great production potential and high economic benefits. Improving its photosynthesis efficiency is crucial for increasing yield. Maize photosynthesis occurs mainly through the C4 pathway, and NADP-ME (NADP-malic enzyme) is a key enzyme in the photosynthetic carbon assimilation pathway of C4 plants. ZmC4-NADP-ME catalyzes the release of CO₂ from oxaloacetate into the Calvin cycle in the maize bundle sheath. Brassinosteroid (BL) can improve photosynthesis; however, its molecular mechanism of action remains unclear. In this study, transcriptome sequencing of maize seedlings treated with epi-brassinolide (EBL) showed that differentially expressed genes (DEGs) were significantly enriched in photosynthetic antenna proteins, porphyrin and chlorophyll metabolism, and photosynthesis pathways. The DEGs of C4-NADP-ME and pyruvate phosphate dikinase in the C4 pathway were significantly enriched in EBL treatment. Co-expression analysis showed that the transcription level of ZmNF-YC2 and ZmbHLH157 transcription factors was increased under EBL treatment and moderately positively correlated with ZmC4-NADP-ME. Transient overexpression of protoplasts revealed that ZmNF-YC2 and ZmbHLH157 activate C4-NADP-ME promoters. Further experiments showed ZmNF-YC2 and ZmbHLH157 transcription factor binding sites on the -1616 bp and -1118 bp ZmC4 NADP-ME promoter. ZmNF-YC2 and ZmbHLH157 were screened as candidate transcription factors mediating brassinosteroid hormone regulation of the ZmC4 NADP-ME gene. The results provide a theoretical basis for improving maize yield using BR hormones.

Fe-Based Nanomaterial-Induced Root Nodulation Is Modulated by Flavonoids to Improve Soybean (Glycine max) Growth and Quality

Innovative technology to increase efficient nitrogen (N) use while avoiding environmental damages is needed because of the increasing food demand of the rapidly growing global population. Soybean (Glycine max) has evolved a complex symbiosis with N-fixing bacteria that forms nodules to fix N. Herein, foliar application of 10 mg L^-1 Fe₇(PO₄)₆ and Fe₃O₄ nanomaterials (NMs) (Fe-based NMs) promoted soybean growth and root nodulation, thus improving the yield and quality over that of the unexposed control, EDTA-control, and 1 and 5 mg L^-1 NMs. Mechanistically, flavonoids, key signaling molecules at the initial signaling steps in nodulation, were increased by more than 20% upon exposure to 10 mg L^-1 Fe-based NMs, due to enhanced key enzyme (phenylalanine ammonia-lyase, PAL) activity and up-regulation of flavonoid biosynthetic genes (GmPAL, GmC4H, Gm4CL, and GmCHS). Accumulated flavonoids were secreted to the rhizosphere, recruiting rhizobia for colonization. Fe₇(PO₄)₆ NMs increased Allorhizobium by 87.3%, and Fe₃O₄ NMs increased Allorhizobium and Mesorhizobium by 142.2% and 34.9%, leading to increased root nodules by 50.0% and 35.4% over the unexposed control, respectively. Leghemoglobin content was also noticeably improved by 8.2-46.5% upon Fe-based NMs. The higher levels of nodule number and leghemoglobin content resulted in enhanced N content by 15.5-181.2% during the whole growth period. Finally, the yield (pod number and grain biomass) and quality (flavonoids, soluble protein, and elemental nutrients) were significantly increased more than 14% by Fe-based NMs. Our study provides an effective nanoenabled strategy for inducing root nodules to increase N use efficiency, and then both yield and quality of soybean.

Co-Application of 24-Epibrassinolide and Titanium Oxide Nanoparticles Promotes Pleioblastus pygmaeus Plant Tolerance to Cu and Cd Toxicity by Increasing Antioxidant Activity and Photosynthetic Capacity and Reducing Heavy Metal Accumulation and Translocation

The integrated application of nanoparticles and phytohormones was explored in this study as a potentially eco-friendly remediation strategy to mitigate heavy metal toxicity in a bamboo species (Pleioblastus pygmaeus) by utilizing titanium oxide nanoparticles (TiO₂-NPs) and 24-epibrassinolide (EBL). Hence, an in vitro experiment was performed to evaluate the role of 100 µM TiO₂ NPs and 10⁻⁸ M 24-epibrassinolide individually and in combination under 100 µM Cu and Cd in a completely randomized design using four replicates. Whereas 100 µM of Cu and Cd reduced antioxidant activity, photosynthetic capacity, plant tolerance, and ultimately plant growth, the co-application of 100 µM TiO₂ NPs and 10⁻⁸ M EBL+ heavy metals (Cu and Cd) resulted in a significant increase in plant antioxidant activity (85%), nonenzymatic antioxidant activities (47%), photosynthetic pigments (43%), fluorescence parameters (68%), plant growth (39%), and plant tolerance (41%) and a significant reduction in the contents of malondialdehyde (45%), hydrogen peroxide (36%), superoxide radical (62%), and soluble protein (28%), as well as the percentage of electrolyte leakage (49%), relative to the control. Moreover, heavy metal accumulation and translocation were reduced by TiO₂ NPs and EBL individually and in combination, which could improve bamboo plant tolerance.

Brassinosteroids and metalloids: Regulation of plant biology

Metalloid contamination in the environment is one of the serious concerns posing threat to our ecosystems. Excess of metalloid concentrations (including antimony, arsenic, boron, selenium etc.) in soil results in their over accumulation in plant tissues, which ultimately causes phytotoxicity and their bio-magnification. So, it is very important to find some ecofriendly approaches to counter negative impacts of above mentioned metalloids on plant system. Brassinosteroids (BRs) belong to family of plant steroidal hormones, and are considered as one of the ecofriendly way to counter metalloid phytotoxicity. This phytohormone regulates the plant biology in presence of metalloids by modulating various key biological processes like cell signaling, primary and secondary metabolism, bio-molecule crosstalk and redox homeostasis. The present review explains the in-depth mechanisms of BR regulated plant responses in presence of metalloids, and provides some biotechnological aspects towards ecofriendly management of metalloid contamination.

Zinc oxide nanoparticles alleviates the adverse effects of cadmium stress on Oryza sativa via modulation of the photosynthesis and antioxidant defense system

Cadmium (Cd) is a trace element causing severe toxicity symptoms in plants, besides posing hazardous fitness issue due to its buildup in the human body through food chain. Nanoparticles (NPs) are recently employed as a novel strategy to directly ameliorate the Cd stress and acted as nano-fertilizers. The intend of the current study was to explore the effects of zinc oxide nanoparticles (ZnO-NPs; 50 mg/L) on plant growth, photosynthetic activity, elemental status and antioxidant activity in Oryza sativa (rice) under Cd (0.8 mM) stress. To this end, the rice plants are treated by Cd stress at 15 days after sowing (DAS), and the treatment was given directly into the soil. Supply of ZnO-NPs as foliar spray was given for five consecutive days from 30 to 35 DAS, and sampling was done at 45 DAS. However, rice plants supplemented with ZnO-NPs under the Cd toxicity revealed significantly increased shoot length (SL; 34.0%), root fresh weight (RFW; 30.0%), shoot dry weight (SDW; 23.07%), and root dry weight (RDW; 12.24%). Moreover, the ZnO-NPs supplement has also positive effects on photosynthesis related parameters, SPAD value (40%), chloroplast structure, and qualitatively high fluorescence observed by confocal microscopy even under Cd stress. ZnO-NPs also substantially prevented the increases of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) triggered by Cd. Physiological and biochemical analysis showed that ZnO-NPs increased enzymatic activities of superoxide dismutase (SOD; 59%), catalase (CAT; 52%), and proline (17%) that metabolize reactive oxygen species (ROS); these increases coincided with the changes observed in the H₂O₂ and MDA accumulation after ZnO-NPs application. In conclusion, ZnO-NPs application to foliage has great efficiency to improve biomass, photosynthesis, protein, antioxidant enzymes activity, mineral nutrient contents and reducing Cd levels in rice. This can be attributed mainly from reduced oxidative damage resulted due to the ZnO-NPs application.

24-epibrassinolide alleviates postharvest yellowing of broccoli via improving its antioxidant capacity

Postharvest crop yellowing is a major concern in the broccoli industry. The effect and underlying mechanisms of 24-epibrassinolide (EBR) treatment on yellowing in postharvest broccoli were investigated. Treatment with 2 µM EBR markedly inhibited the increase of the yellowing index and L* values, causing higher retention of the metric hue angle and chlorophyll content compared to the control. Treatment also alleviated oxidative damage by preventing the accumulation of malondialdehyde and superoxide anion (O₂^•-). The ascorbic acid content of broccoli reached its lowest value at the end of its shelf life, whereas that of the treated sample was obviously higher than the control. Moreover, treated broccoli exhibited higher superoxide dismutase, ascorbate peroxidase, and phenylalanine ammonia-lyase activities. Multivariate statistical analysis further demonstrated the effective enhancement of EBR treatment on antioxidant enzymes. These results indicate that exogenous application of EBR ameliorates postharvest yellowing by improving the antioxidant capacity of broccoli.

Exogenous 24-Epibrassinolide stimulates root protection, and leaf antioxidant enzymes in lead stressed rice plants: Central roles to minimize Pb content and oxidative stress

Lead (Pb) is an environmental pollutant that negatively affects rice plants, causing damage to the root system and chloroplast structures, as well as reducing growth. 24-Epibrasnolide (EBR) is a plant growth regulator with a high capacity to modulate antioxidant metabolism. The objective of this research was to investigate whether exogenous EBR application can mitigate oxidative damage in Pb-stressed rice plants, measure anatomical structures and evaluate physiological and biochemical responses connected with redox metabolism. The experiment was randomized with four treatments, including two lead treatments (0 and 200 μM PbCl₂, described as - Pb and + Pb, respectively) and two treatments with brassinosteroid (0 and 100 nM EBR, described as - EBR and + EBR, respectively). The results revealed that plants exposed to Pb suffered significant disturbances, but the EBR alleviated the negative interferences, as confirmed by the improvements in the root structures and antioxidant system. This steroid stimulated the root structures, increasing the epidermis thickness (26%) and aerenchyma area (50%), resulting in higher protection of this tissue against Pb²⁺ ions. Additionally, EBR promoted significant increases in superoxide dismutase (26%), catalase (24%), ascorbate peroxidase (54%) and peroxidase (63%) enzymes, reducing oxidative stress on the photosynthetic machinery in Pb-stressed plants. This research proved that EBR mitigates the toxic effects generated by Pb in rice plants.

Improving Performance of Salt-Grown Crops by Exogenous Application of Plant Growth Regulators

Soil salinity is one of the major abiotic stresses restricting plant growth and development. Application of plant growth regulators (PGRs) is a possible practical means for minimizing salinity-induced yield losses, and can be used in addition to or as an alternative to crop breeding for enhancing salinity tolerance. The PGRs auxin, cytokinin, nitric oxide, brassinosteroid, gibberellin, salicylic acid, abscisic acid, jasmonate, and ethylene have been advocated for practical use to improve crop performance and yield under saline conditions. This review summarizes the current knowledge of the effectiveness of various PGRs in ameliorating the detrimental effects of salinity on plant growth and development, and elucidates the physiological and genetic mechanisms underlying this process by linking PGRs with their downstream targets and signal transduction pathways. It is shown that, while each of these PGRs possesses an ability to alter plant ionic and redox homeostasis, the complexity of interactions between various PGRs and their involvement in numerous signaling pathways makes it difficult to establish an unequivocal causal link between PGRs and their downstream effectors mediating plants' adaptation to salinity. The beneficial effects of PGRs are also strongly dependent on genotype, the timing of application, and the concentration used. The action spectrum of PGRs is also strongly dependent on salinity levels. Taken together, this results in a rather narrow "window" in which the beneficial effects of PGR are observed, hence limiting their practical application (especially under field conditions). It is concluded that, in the light of the above complexity, and also in the context of the cost-benefit analysis, crop breeding for salinity tolerance remains a more reliable avenue for minimizing the impact of salinity on plant growth and yield. Further progress in the field requires more studies on the underlying cell-based mechanisms of interaction between PGRs and membrane transporters mediating plant ion homeostasis.

Zinc oxide nanoparticles and 24-epibrassinolide alleviates Cu toxicity in tomato by regulating ROS scavenging, stomatal movement and photosynthesis

Nanoparticles (NPs) have recently emerged as potential agents for plants to ameliorate abiotic stresses by acting as nano-fertilizers. In this regard, the influence of the zinc oxide nanoparticles (ZnO-NPs) on plant responses to copper (Cu) stress has been poorly understood. Hence, the present study was executed to explore the role of ZnO-NPs (foliar) and 24-epibrassinolide (EBL; root dipping) individually or in combined form in the resilience of tomato (Solanum lycopersicum) plant to Cu stress. Tomato seeds were sown to make the nursery; and at 20 days after sowing (DAS) the plantlets were submerged in 10-8 M of EBL solution for 2 h, and subsequently transplanted in the soil-filled earthen pots. Cu concentration (100 mg kg-1) was applied to the soil at 30 DAS, whereas at 35 DAS plants were sprinkled with double distilled water (DDW; control), 50 mg/L of Zinc (Zn) and 50 mg/L of ZnO-NPs; and plant performance were evaluated at 45 DAS. It was evident that Cu-stress reduced photosynthesis (17.3%), stomatal conductance (18.1%), plant height (19.7%), and nitrate reductase (NR) activity (19.2%), but increased malondialdehyde (MDA; 29.4%), superoxide radical (O2-; 22.3%) and hydrogen peroxide (H2O2; 26.2%) content in S. lycopersicum. Moreover, ZnO-NPs and/or EBL implemented via different modes improved photosynthetic activity, stomatal aperture, growth, cell viability and activity of antioxidant enzymes and proline that augmented resilience of tomato plants to Cu stress. These observations depicted that application of ZnO-NPs and EBL could be a useful approach to assist Cu confiscation and stress tolerance against Cu in tomato plants grown in Cu contaminated sites.

Nanoparticles enhances the salinity toxicity tolerance in Linum usitatissimum L. by modulating the antioxidative enzymes, photosynthetic efficiency, redox status and cellular damage

The contribution of nanoparticles (NPs) in physiology of the plants became the new area of interest for the physiologists; as it is very much cost effective compared to the phytohormones. Our present investigation was also based on this interest in which the same doses (50 mg/L) of four different NPs were sprayed on stressed and non-stressed foliage. The experiment was conducted to assess the impact of four NPs viz., zinc oxide (ZnO), silicon dioxide (SiO₂), titanium dioxide (TiO₂), and ferric oxide (Fe₂O₃) on the morphology and physiology of linseed in the presence of sodium chloride (NaCl). Plants responded positively to all the treated NPs and improved the growth, carbon and nutrient assimilation, while salt stress increased the content of proline, hydrogen peroxide and superoxide anion. Application of NPs over the stressed plants further increased the antioxidant enzymatic system and other physiochemical reactions. Results indicate that application of NPs increased the growth and physiology of the plant and also increased the salt tolerance capacity of the plant.

Exogenous DA-6 Improves the Low Night Temperature Tolerance of Tomato Through Regulating Cytokinin

Low night temperature (LNT) causes environmental stress and has a severe and negative impact on plant growth and productivity. Synthetic elicitors can regulate plant growth and induce defense mechanisms from this type of stress. Here, we evaluated the effect of the exogenous growth regulator diethyl aminoethyl hexanoate (DA-6) in tomato leaf response to LNT stress. Our results showed that exogenous DA-6 activates the expression of chlorophyll synthesis and photosystem-related genes, and results in higher photosynthetic activity and chlorophyll production. Furthermore, DA-6 can regulate the synthesis of endogenous cytokinin (CTK) and the expression of decomposition genes to stabilize chloroplast structure, reduce oxidative damage, and maintain the photochemical activity of tomato leaves under LNT stress. DA-6 maintains a high level of ABA content and induces the expression of CBF genes, indicating that DA-6 may participate in the cold response signaling pathway and induce the expression of downstream low temperature response genes and accumulation of compatible osmolytes. This study unravels a mode of action by which plant growth regulators can improve low temperature tolerance and provides important considerations for their application to alleviate the harmful effects of cold stress.

Foliar spray of Auxin/IAA modulates photosynthesis, elemental composition, ROS localization and antioxidant machinery to promote growth of Brassica juncea

Auxins (Aux) are primary growth regulators that regulate almost every aspect of growth and development in plants. It plays a vital role in various plant processes besides controlling the key aspects of cell division, cell expansion, and cell differentiation. Considering the significance of Aux, and its potential applications, a study was conducted to observe the impact of indole acetic acid (IAA), a most active and abundant form of Aux on Brassica juncea plants growing under natural environmental conditions. Different concentrations (0, 10^-10, 10^-8, 10^-6 M) of IAA were applied once in a day at 25-day stage of growth for 5 days, consecutively. Various parameters (growth, photosynthetic, biochemical, oxidative biomarkers and nutrient composition) were assessed at different days after sowing (DAS). Scanning electron microscopy (SEM) of leaf stomata, reactive oxygen species (ROS) localization in leaf and roots, and confocal microscopy were also conducted. The results revealed that all the IAA concentrations were effective in growth promotion and ROS reduction, however, the 10^-8 M of IAA exhibited the maximum improvement in all the above mentioned parameters as compared to the control.

Melatonin modulates photosynthesis, redox status, and elemental composition to promote growth of Brassica juncea-a dose-dependent effect

Melatonin (MEL) is an antioxidant molecule, present throughout plant kingdom, animals, and microbes. It is a well-known free radical scavenger and modulates growth and development in plants against various abiotic and biotic stresses. The present study was done to investigate the role of MEL as a foliar spray on the morphological, physiological, and biochemical parameters in Brassica juncea cv. Varuna. Five different doses (10, 20, 30, 40, or 50 μM) of MEL were applied as foliar spray to the leaf of plant at 25 days after sowing (DAS) and continued up to 30 DAS once in a day. The plants were sampled at 30, 45, and 60 DAS to assess various parameters. The present results indicate that most of the parameters, i.e., growth, photosynthetic, nutrients, and enzyme activities increased in a concentration dependent manner. MEL application reduced the accumulation of reactive oxygen species (ROS) by enhancing the antioxidant enzyme activities. Microscopic examinations further revealed a significant increase in the size of the stomatal aperture in the presence of MEL. Out of the various concentrations tested, 40 μM of MEL proved best and can be used for further studies.

Phytoremediation of Cadmium Contaminated Soil Using Brassica juncea: Influence on PSII Activity, Leaf Gaseous Exchange, Carbohydrate Metabolism, Redox and Elemental Status

Phytoremediation is an ecologically and economically feasible technique to remove heavy metal from soil. The aim of the study was to examine cadmium (Cd) toxicity and phytoremediation aptitude of Brassica juncea. In the present study, plants survived when exposed to different levels of Cd (0, 25, 50 and 100 mg/kg soil) and accumulated a large amount of Cd in its root and shoot. Translocation factor (TF) of Cd from root to shoot was > 1 at both 45 and 60-day stage of growth suggesting that B. juncea is a hyperaccumulator and strong candidate for phytoextraction of Cd. Alongside, Cd impaired photolysis of water, PSII activity, nutrient uptake, photosynthesis and sugar accumulation in the plant. Cd-generated oxidative stress restricts the growth of B. juncea. The toxic effect of Cd was more pronounced at 45-day stage of growth signifying the drifting of plant towards acquirement of exclusion strategy.

Exogenous ascorbic acid induces systemic heat stress tolerance in tomato seedlings: transcriptional regulation mechanism

The current study was devoted to assessing the impact of exogenous ascorbic acid (AsA) in inducing systemic thermotolerance against acute heat stress in tomato (Solanum lycopersicum) seedlings. There were four treatment groups including untreated control (CK), heat-stressed tomato (HS: exposure to 40 °C for 8 h), and treated with ascorbic acid (0.5 mM AsA), and the last group includes both the exogenous application of ascorbic acid and heat stress (AsA + HS). The HS led to leaf curling and mild wilting while plants treated with AsA displayed similar phenotype with control plants, approving that AsA eliminated the injurious effects of the heat stress. The oxidative damage to cell components was confirmed by higher levels of hydrogen peroxide, lipid peroxidation, electrolyte leakage, total oxidant status, and oxidative stress index. Moreover, acute heat stress significantly reduced the photosynthetic pigment contents, and nutrient contents in tomato seedling leaves. In contrast, ascorbic acid postulated a priming effect on tomato roots and, substantially, alleviated heat stress effects on seedlings through reducing the oxidative damage and increasing the contents of ascorbic acid, proline, photosynthetic pigments, and upregulation of heat shock proteins in leaves. Ascorbic acid seems to be a key signaling molecule which enhanced the thermotolerance of tomato plants.

Transcriptome analysis reveals a positive effect of brassinosteroids on the photosynthetic capacity of wucai under low temperature

Background

Brassinosteroids (BRs) have a positive effect on many processes during plant growth and development, and in response to various abiotic stressors. Low-temperature (LT) stress constricts the geographic distribution, growth, and development of wucai (Brassica campestris L. ssp. chinensis var. rosularis Tsen). However, there is little information on the global gene expression of BRs under LT stress in wucai. In this study, the molecular roles of 24-epibrassinolide (EBR) after exogenously application, were explored by RNA sequencing under LT conditions.

Results

According to the Gene Ontology (GO) term and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses, photosynthesis was significantly enriched after spraying EBR under LT. The transcripts encoding the photosystem II (PSII) oxygen-evolving enhancer protein, photosystem I (PSI) subunit, light-harvesting chlorophyll protein complexes I and II, and ferredoxin were up-regulated after the application of EBR. Transcripts encoding several key enzymes involved in chlorophyll biosynthesis were also up-regulated, accompanied by significant differences in the contents of 5-aminolevulinic acid (ALA), porphobilinogen (PBG), protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-proto IX), protochlorophyllide (Pchl), and photosynthetic pigments. Notably, transcriptional and physiological analyses revealed that under LT stress, plant responses to EBR involved a major reorientation of photosynthesis, as well as porphyrin and chlorophyll metabolism.

Conclusion

This study explored the role of EBR as an LT stress tolerance mechanism in wucai. At the transcription level, LT tolerance manifests as an enhancement of photosynthesis, and the amelioration of porphyrin and chlorophyll metabolism.

Exogenous application of β-sitosterol mediated growth and yield improvement in water-stressed wheat (Triticum aestivum) involves up-regulated antioxidant system

Water stress reduces crop production significantly, and climate change has further aggravated the problem mainly in arid and semi-arid regions. This was the first study on the possible effects of β-sitosterol application in ameliorating the deleterious changes in wheat induced by water stress under field condition and drip irrigation regimes. A field experiment with the split-plot design was conducted, and wheat plants were foliar sprayed with four β-sitosterol (BBS) concentrations (0, 25, 75, and 100 mg L^-1) and two irrigation regimes [50 and 100% of crop evapotranspiration (ET_c)]. Water stress without BBS treatment reduced biological yield, grain yield, harvest index, and photosynthetic efficiency significantly by 28.9%, 42.8%, 19.6%, and 20.5% compared with the well-watered plants, respectively. Proline content increased in water-stressed and BSS-treated plants, owing to a significant role in cellular osmotic adjustment. Application of BSS was effective in reducing the generation of hydrogen peroxide (H₂O₂) and hence the malondialdehyde content significantly in water-stressed and well-watered wheat plants. Application of BSS up-regulated the activity of antioxidant enzymes (SOD, CAT, POD, and APX) significantly and increased the content of tocopherol, ascorbic acid, and carotene thereby reducing the levels of reactive oxygen species. The increased antioxidant system in BSS treated plants was further supported by the expression level of SOD and dehydrin genes in both water-stressed and well-watered plants. In the present study, the application of BBS at 100 mg L^-1 was beneficial and can be recommended for improving the growth and yield of the wheat crop under water stress.

Pesticide mediated oxidative stress induces genotoxicity and disrupts chromatin structure in fenugreek (Trigonella foenum - graecum L.) seedlings

Here we report cytototoxic and genotoxic potentials of four commonly used pesticides, including, tricyclazole, thiabendazole (fungicides), plethora and slash-360 (insecticides) in the non-target tropical crop plant Trigonella foenum - graecum L. (fenugreek). Three different concentrations of the selected pesticides were used. For fungicides, 0.05% and for insecticides, 0.1% concentration represents recommended doses, while, 2X and 4X concentrations of the recommended dose were used to test their phytotoxic effects. Inhibition of germination and seedling growth were clearly observed at 4X concentration of the pesticides. Tricyclazole and plethora showed more pronounced effects than the other two agrochemicals. The pesticides, particularly at 4X concentrations clearly induced oxidative stress and cytotoxic effects in Trigonella seedlings with appreciable reduction in mitotic index, induction of chromosomal abnormalities in root meristematic cell and decreased level of accumulation of some key cell cycle regulators, including CDK1, CDK2 and Cyclin B1.Detection of accumulation of DNA double strand breaks and histone H2AX phosphorylation in pesticide treated seedlings have revealed direct genotoxic effects of the selected pesticides. Overall, our results provide insights into the mechanism of pesticide induced cytotoxic and genotoxic effects in plant genome with future implications for designing pesticides to minimize their deleterious effects on non-target crop plants.

MdBZR1 and MdBZR1-2like Transcription Factors Improves Salt Tolerance by Regulating Gibberellin Biosynthesis in Apple

Brassinosteroids (BRs) are a group of plant steroid hormones that play important roles in regulating plant development. In addition, BRs show considerable functional redundancy with other plant hormones such as gibberellins (GAs). BRASSINAZOLE RESISTANT1 (BZR1) and BRI1-EMS-SUPPRESSOR1 (BES1) transcription factors are negative feedback regulators of BR biosynthesis. This study provides evidence for the roles of MdBZR1 and MdBZR1-2like in promoting GA production. These results also show that BRs regulate GA biosynthesis to improve salt tolerance in apple calli. Moreover, this research proposes a regulatory model, in which MdBZR1 and MdBZR1-2like bind to the promoters of GA biosynthetic genes to regulate their expression in a BR-dependent manner. The expression of key GA biosynthetic genes, MdGA20ox1, MdGA20ox2, and MdGA3ox1 in yeast helps to maintain normal growth even under intense salt stress. In summary, this study underscores the roles of MdBZR1 and MdBZR1-2like in improving salt tolerance by regulating GA biosynthesis in apple calli.