RNAi-Mediated Suppression of OsBBTI5 Promotes Salt Stress Tolerance in Rice

This study explores the impact of RNAi in terms of selectively inhibiting the expression of the OsBBTI5 gene, with the primary objective of uncovering its involvement in the molecular mechanisms associated with salt tolerance in rice. OsBBTI5, belonging to the Bowman-Birk inhibitor (BBI) family gene, is known for its involvement in plant stress responses. The gene was successfully cloned from rice, exhibiting transcriptional self-activation in yeast. A yeast two-hybrid assay confirmed its specific binding to OsAPX2 (an ascorbate peroxidase gene). Transgenic OsBBTI5-RNAi plants displayed insensitivity to varying concentrations of 24-epibrassinolide in the brassinosteroid sensitivity assay. However, they showed reduced root and plant height at high concentrations (10 and 100 µM) of GA3 immersion. Enzyme activity assays revealed increased peroxidase (POD) and superoxide dismutase (SOD) activities and decreased malondialdehyde (MDA) content under 40-60 mM NaCl. Transcriptomic analysis indicated a significant upregulation of photosynthesis-related genes in transgenic plants under salt stress compared to the wild type. Notably, this study provides novel insights, suggesting that the BBI gene is part of the BR signaling pathway, and that OsBBTI5 potentially enhances stress tolerance in transgenic plants through interaction with the salt stress-related gene OsAPX2.

Exogenous Brassinosteroid Enhances Zinc tolerance by activating the Phenylpropanoid Biosynthesis pathway in Citrullus lanatus L

Zinc (Zn) is an important element in plants, but over-accumulation of Zn is harmful. The phytohormone brassinosteroids (BRs) play a key role in regulating plant growth, development, and response to stress. However, the role of BRs in watermelon (Citrullus lanatus L.) under Zn stress, one of the most important horticultural crops, remains largely unknown. In this study, we revealed that 24-epibrassinolide (EBR), a bioactive BR enhanced Zn tolerance in watermelon plants, which was related to the EBR-induced increase in the fresh weight, chlorophyll content, and net photosynthetic rate (Pn) and decrease in the content of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and Zn in watermelon leaves. Through RNA deep sequencing (RNA-seq), 350 different expressed genes (DEG) were found to be involved in the response to Zn stress after EBR treatment, including 175 up-regulated DEGs and 175 down-regulated DEGs. The up-regulated DEGs were significantly enriched in 'phenylpropanoid biosynthesis' pathway (map00940) using KEGG enrichment analysis. The gene expression levels of PAL, 4CL, CCR, and CCoAOMT, key genes involved in phenylpropanoid pathway, were significantly induced after EBR treatment. In addition, compared with Zn stress alone, EBR treatment significantly promoted the activities of PAL, 4CL, and POD by 30.90%, 20.69%, and 47.28%, respectively, and increased the content of total phenolic compounds, total flavonoids, and lignin by 23.02%, 40.37%, and 29.26%, respectively. The present research indicates that EBR plays an active role in strengthening Zn tolerance, thus providing new insights into the mechanism of BRs enhancing heavy metal tolerance.

Effects of Plant Regulators on the Seed Germination and Antioxidant Enzyme Activity of Cotton under Compound Salt Stress

Salinity stress significantly hampers cotton seed germination and seedling growth. Employing plant growth regulators stands out as an effective strategy to mitigate salt stress. In this study, we assessed the impact of varying concentrations of natural composite salt conditions (0%, 0.6%, and 1.2%) on cotton seed germination, seedling growth, and physiology. Additionally, we explored the effects of compound sodium nitrophenolate (CSN: 2 mg·L-1 and 10 mg·L-1), 24-epibrassinolide (EBR: 0.02 mg·L-1 and 0.1 mg·L-1), and gibberellic acid (GA: 60 mg·L-1 and 300 mg·L-1), against a control (CK: distilled water) group. The results indicate that with an increase in the composite salt concentration, the germination potential (GP) and germination rate (GR) of cotton seeds gradually decrease. Simultaneously, the fresh weight and root vitality of seedlings also correspondingly decrease, while the degree of membrane lipid peroxidation increases. Under high-salt (1.2%) conditions, soaking treatments with CSN and EBR significantly enhance both GP (45-59% and 55-64%) and GR (30-33% and 39-36%) compared to the CK. However, the GA treatment does not increase the GP and GR of cotton. Moreover, under high-salt (1.2%) conditions, CSN and EBR treatments result in the increased activities of superoxide dismutase (56-66% and 71-80%), peroxidase (20-24% and 37-51%), and catalase (26-32% and 35-46%). Consequently, cotton exhibits a relatively good tolerance to natural composite salts. Soaking treatments with CSN and EBR effectively improve cotton germination by enhancing antioxidant enzyme activities, thereby strengthening cotton's tolerance to salt stress. These findings offer new insights for enhancing the salt tolerance of cotton.

Physiological Characteristics and Transcriptome Analysis of Exogenous Brassinosteroid-Treated Kiwifruit

Brassinosteroids (BRs) play pivotal roles in improving plant stress tolerance. To investigate the mechanism of BR regulation of salt tolerance in kiwifruit, we used 'Hongyang' kiwifruit as the test material. We exposed the plants to 150 mmol/L NaCl stress and irrigated them with exogenous BR (2,4-epibrassinolide). The phenotypic analysis showed that salt stress significantly inhibited photosynthesis in kiwifruit, leading to a significant increase in the H2O2 content of leaves and roots and a significant increase in Na+/K+, resulting in oxidative damage and an ion imbalance. BR treatment resulted in enhanced photosynthesis, reduced H2O2 content, and reduced Na+/K+ in leaves, alleviating the salt stress injury. Furthermore, transcriptome enrichment analysis showed that the differentially expressed genes (DEGs) related to BR treatment are involved in pathways such as starch and sucrose metabolism, pentose and glucuronate interconversions, and plant hormone signal transduction, among others. Among the DEGs involved in plant hormone signal transduction, those with the highest expression were involved in abscisic acid signal transduction. Moreover, there was a significant increase in the expression of the AcHKT1 gene, which regulates ion transduction, and the antioxidant enzyme AcFSD2 gene, which is a key gene for improving salt tolerance. The data suggest that BRs can improve salt tolerance by regulating ion homeostasis and reducing oxidative stress.

Assessing the effects of 24-epibrassinolide and yeast extract at various levels on cowpea's morphophysiological and biochemical responses under water deficit stress

BACKGROUND

Due to the factor of water deficit, which has placed human food security at risk by causing a 20% annual reduction in agricultural products, addressing this growing peril necessitates the adoption of inventive strategies aimed at enhancing plant tolerance. One such promising approach is employing elicitors such as 24-epibrassinolide (EBR) and yeast extract, which are potent agents capable of triggering robust defense responses in plants. By employing these elicitors, crops can develop enhanced adaptive mechanisms to combat water deficit and improve their ability to withstand drought condition. This study investigates the impact of different levels of EBR (0, 5, 10 µm) and yeast extract (0 and 12 g/l) on enhancing the tolerance of cowpea to water deficit stress over two growing seasons.

RESULTS

The findings of this study demonstrate that, the combined application of EBR (especially 10 µm) and yeast extract (12 g/l) can increase seed yield (18%), 20-pod weight (16%), the number of pods per plant (18%), total chlorophyll content (90%), and decrease malondialdehyde content (45%) in cowpea, compared to plants grown under water deficit stress without these treatments. Upon implementing these treatments, impressive results were obtained, with the highest recorded values observed for the seed yield (1867.55 kg/ha), 20-pod weight (16.29 g), pods number per plant (9), and total chlorophyll content (19.88 mg g-1 FW). The correlation analysis indicated a significant relationship between the seed yield, and total chlorophyll (0.74**), carotenoids (0.82**), weight of 20 seeds (0.67**), and number of pods (0.90**). These traits should be prioritized in cowpea breeding programs focusing on water deficit stress.

CONCLUSIONS

The comprehensive exploration of the effects of EBR and yeast extract across various levels on cowpea plants facing water deficit stress presents a pivotal contribution to the agricultural domain. This research illuminates a promising trajectory for future agricultural practices and users seeking sustainable solutions to enhance crops tolerance. Overall, the implications drawn from this study contribute significantly towards advancing our understanding of plant responses to water deficit stress while providing actionable recommendations for optimizing crop production under challenging environmental conditions.

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.

24-Epibrassinolide Facilitates Adventitious Root Formation by Coordinating Cell-Wall Polyamine Oxidase- and Plasma Membrane Respiratory Burst Oxidase Homologue-Derived Reactive Oxygen Species in Capsicum annuum L

Adventitious root (AR) formation is a critical process in cutting propagation of horticultural plants. Brassinosteroids (BRs) have been shown to regulate AR formation in several plant species; however, little is known about their exact effects on pepper AR formation, and the downstream signaling of BRs also remains elusive. In this study, we showed that treatment of 24-Epibrassinolide (EBL, an active BR) at the concentrations of 20-100 nM promoted AR formation in pepper (Capsicum annuum). Furthermore, we investigated the roles of apoplastic reactive oxygen species (ROS), including hydrogen peroxide (H₂O₂) and superoxide radical (O₂^•-), in EBL-promoted AR formation, by using physiological, histochemical, bioinformatic, and biochemical approaches. EBL promoted AR formation by modulating cell-wall-located polyamine oxidase (PAO)-dependent H₂O₂ production and respiratory burst oxidase homologue (RBOH)-dependent O₂^•- production, respectively. Screening of CaPAO and CaRBOH gene families combined with gene expression analysis suggested that EBL-promoted AR formation correlated with the upregulation of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in the AR zone. Transient expression analysis confirmed that CaPAO1 was able to produce H₂O₂, and CaRBOH2, CaRBOH5, and CaRBOH6 were capable of producing O₂^•-. The silencing of CaPAO1, CaRBOH2, CaRBOH5, and CaRBOH6 in pepper decreased the ROS accumulation and abolished the EBL-induced AR formation. Overall, these results uncover one of the regulatory pathways for BR-regulated AR formation, and extend our knowledge of the functions of BRs and of the BRs-ROS crosstalk in plant development.

Assessment of Biological Activity of 28-Homobrassinolide via a Multi-Level Comparative Analysis

Brassinosteroids (BRs) play vital roles in the plant life cycle and synthetic BRs are widely used to increase crop yield and plant stress tolerance. Among them are 24R-methyl-epibrassinolide (24-EBL) and 24S-ethyl-28-homobrassinolide (28-HBL), which differ from brassinolide (BL, the most active BR) at the C-24 position. Although it is well known that 24-EBL is 10% active as BL, there is no consensus on the bioactivity of 28-HBL. A recent outpouring of research interest in 28-HBL on major crops accompanied with a surge of industrial-scale synthesis that produces mixtures of active (22R,23R)-28-HBL and inactive (22S,23S)-28HBL, demands a standardized assay system capable of analyzing different synthetic "28-HBL" products. In this study, the relative bioactivity of 28-HBL to BL and 24-EBL, including its capacity to induce the well-established BR responses at molecular, biochemical, and physiological levels, was systematically analyzed using the whole seedlings of the wild-type and BR-deficient mutant of Arabidopsis thaliana. These multi-level bioassays consistently showed that 28-HBL exhibits a much stronger bioactivity than 24-EBL and is almost as active as BL in rescuing the short hypocotyl phenotype of the dark-grown det2 mutant. These results are consistent with the previously established structure-activity relationship of BRs, proving that this multi-level whole seedling bioassay system could be used to analyze different batches of industrially produced 28-HBL or other BL analogs to ensure the full potential of BRs in modern agriculture.

Interactive effect of 24-epibrassinolide and plant growth promoting rhizobacteria inoculation restores photosynthetic attributes in Brassica juncea L. under chlorpyrifos toxicity

Chlorpyrifos (CP) is a commonly used organophosphorous pesticide that is frequently utilised in the agricultural industry because of its great efficiency and inexpensive cost. The focus of the present study was to assess the impact of CP toxicity on Brassica juncea L. and to unravel the ameliorative potential of phytohormone, 24-epibrassinolide (EBL) mediated plant-microbe (Pseudomonas aeruginosa (B1), Burkholderia gladioli (B2)) interaction in B. juncea L. The maximum significant increment in the total chlorophyll, carotenoids, xanthophyll, anthocyanin and flavonoid content with EBL and B2 treatment in CP stressed B. juncea seedlings on spectrophotometric analysis were observed. Autofluorescence imaging of photosynthetic pigments i.e. chlorophyll, carotenoids, and total phenols with confocal microscopy showed maximum fluorescence with EBL and B2. Furthermore, when compared to CP stressed seedlings, scanning electron microscopy (SEM) study of the abaxial surface of leaves revealed a recovery in stomatal opening. The supplementation of EBL and PGPR (plant growth promoting rhizobacteria) improved the level of psb A (D1 subunit PSII) and psb B (CP 47 subunit of PSII) genes expression. The expression analysis of chalcone synthase (CHS), Phenylalanine ammonialyase (PAL), Phyotene synthase (PSY) with RT-PCR system showed up-regulation in the expression when supplemented with EBL and PGPR. As a result, the current study suggests that EBL and PGPR together, can reduce CP-induced toxicity in B. juncea seedlings and recovering the seedling biomass.

New Paradigms in Brassinosteroids, Strigolactones, Sphingolipids, and Nitric Oxide Interaction in the Control of Lateral and Adventitious Root Formation

The root system is formed by the primary root (PR), which forms lateral roots (LRs) and, in some cases, adventitious roots (ARs), which in turn may produce their own LRs. The formation of ARs is also essential for vegetative propagation in planta and in vitro and for breeding programs. Root formation and branching is coordinated by a complex developmental network, which maximizes the plant's ability to cope with abiotic stress. Rooting is also a response caused in a cutting by wounding and disconnection from the donor plant. Brassinosteroids (BRs) are steroid molecules perceived at the cell surface. They act as plant-growth-regulators (PGRs) and modulate plant development to provide stress tolerance. BRs and auxins control the formation of LRs and ARs. The auxin/BR interaction involves other PGRs and compounds, such as nitric oxide (NO), strigolactones (SLs), and sphingolipids (SPLs). The roles of these interactions in root formation and plasticity are still to be discovered. SLs are carotenoid derived PGRs. SLs enhance/reduce LR/AR formation depending on species and culture conditions. These PGRs possibly crosstalk with BRs. SPLs form domains with sterols within cellular membranes. Both SLs and SPLs participate in plant development and stress responses. SPLs are determinant for auxin cell-trafficking, which is essential for the formation of LRs/ARs in planta and in in vitro systems. Although little is known about the transport, trafficking, and signaling of SPLs, they seem to interact with BRs and SLs in regulating root-system growth. Here, we review the literature on BRs as modulators of LR and AR formation, as well as their crosstalk with SLs and SPLs through NO signaling. Knowledge on the control of rooting by these non-classical PGRs can help in improving crop productivity and enhancing AR-response from cuttings.

Exogenous 24-epibrassinolide promoted growth and nitrogen absorption and assimilation efficiency of apple seedlings under salt stress

Introduction

High salinity significantly hampers global agricultural productivity. Plants typically undergo lower nitrogen utilization efficiency (NUE) under salt stress. As an active byproduct from brassinolide biosynthesis, 24-epibrassinolide (EBR) is involved in regulating the stress-treated plant N absorption and assimilation. However, the exogenous EBR application effects' on N absorption and assimilation in apple exposed to the salt-stressed condition remains unclear.

Methods

We sprayed exogenous EBR (0.2 mg L^-1) on apple dwarf rootstock (M9T337) seedlings (growing hydroponically) under salt (NaCl) stress in a growth chamber. We analyzed the seedling development, photosynthesis and its-mediated C fixation, N ( NO 3 - ) absorption and assimilation in reponse to exogenous EBR application under salt stress.

Results

The findings demonstrated that NaCl stress greatly hampered seedlings' root growth and that exogenous EBR application obviously alleviated this growth suppression. Exogenous EBR-treated plants under NaCl stress displayed the more ideal root morphology and root activity, stronger salt stress tolerance and photosynthetic capacity as well as higher C- and N-assimilation enzyme activities, NO 3 - ion flow rate and nitrate transporter gene expression level than did untreated plants. Furthermore, the results of isotope labeling noted that exogenous EBR application also enhanced ¹³C-photoassimilate transport from leaves to roots and ¹⁵ NO 3 - transport from roots to leaves under NaCl stress.

Conclusion

Our findings imply that exogenous EBR application, through strengthening photosynthesis, C- and N-assimilation enzyme activities, nitrate absorption and transport as well as synchronized optimizing the distribution of seedlings' C and N, has a fundamental role in improving NUE in apple rootstock seedlings under salt stress.

24-Epibrassinolide confers zinc stress tolerance in watermelon seedlings through modulating antioxidative capacities and lignin accumulation

Zinc (Zn) is an important element in plants, but over-accumulation of Zn is harmful. It is well-known that brassinolide (BR) plays a key role in the regulation of abiotic stress responses in plants. However, the effects of brassinolide on alleviating Zn phytotoxicity in watermelon (Citrullus lanatus L.) seedlings are not clear. The purpose of this study was to study the effect of 24-epibrassinolide (EBR, one of the bioactive BRs) on Zn tolerance of watermelon seedlings and its potential resistance mechanism. Exposure to excessive Zn significantly inhibited shoot and root fresh weight of watermelon, but this could be significantly alleviated by the optimum 0.05 μM EBR. Exogenous spraying EBR increased the pigments and alleviated oxidative damage caused by Zn through reducing Zn accumulation and the levels of reactive oxygen species (ROS) and malonaldehyde (MDA) and increasing the activities of antioxidant enzymes and contents of ascorbic acid (AsA) and glutathione (GSH). Importantly, the relative mRNA levels of antioxidant genesincluding Cu/Zn-superoxidedismutase (Cu-Zn SOD), catalase (CAT), ascorbic acid peroxidase (APX), and glutathione reductase (GR) were significantly induced after EBR treatment. In addition, EBR pre-treatment induced lignin accumulation under Zn stress, and the activity of phenylalanine ammonia-lyase (PAL) and 4-coumaric ligase (4CL), two key enzymes regulating lignin synthesis, also tended to be consistent. Collectively, the present research proves the beneficial effects of EBR in response to Zn stress through enhancing antioxidant defense and lignin accumulation and provides a new insight into the mechanism of BR-enhancing heavy metal tolerance.

A 24-epibrassinolide treatment and intercropping willow with alfalfa increase the efficiency of the phytoremediation of cadmium-contaminated soil

Cadmium contamination in agricultural soils threatens food security and human health, and that has caused widespread concern worldwide. Willow and alfalfa are widely used for the phytoremediation of cadmium (Cd)-contaminated soil, and willow NJU513 is the promising plant for remediating Cd-contaminated soil. In order to discuss the effect of intercropping willow NJU513 with alfalfa on the phytoremediation of Cd-contaminated soil, a pot-culture experiment was conducted in the greenhouse. The result showed that the phytoremediation of Cd-contaminated soil was enhanced by this intercropping because of the 25.90 % increase in the available Cd content. In order to increase the phytoremediation efficiency of Cd in the intercropping treatment, a 24-epibrassinolide (Brs) treatment was designed in the current study. The results showed that the phytoremediation of Cd-contaminated soil by willow and alfalfa improved following a Brs treatment because of the 16.32-74.15 % and 16.91-44.48 % increases in the plant biomass and available Cd content, respectively. Additionally, the extracted Cd by plants in the intercropping treatments with and without Brs was 0.56 and 0.31 mg pot-1, respectively. Transcriptome analyses of willow leaves revealed that Brs up-regulated the expression of genes related to calcium channel activity, calcium and zinc transmembrane transport, photosynthesis, catalase/antioxidant activity, glutathione metabolic processes and detoxification, phagosomes, and vacuoles, and that these upregulated genes promoted plant remediation efficiency and resistance to Cd stress. Brs promoted the phosphate ion transporter activity in willow leaves, which may have enhanced the solubilization of insoluble phosphate minerals by bacterial species (e.g., Vicinamibacterales, Bacillus, and Gaiella) to release Cd, ultimately leading to increased phytoremediation efficiency. In addition, plants with and without Brs treatments induced the bacteria-mediated transformation of available Cd to stable Cd. The study findings may be useful for improving the phytoremediation of Cd-contaminated paddy soil.

Effects of Exogenous α-Naphthaleneacetic Acid and 24-Epibrassinolide on Fruit Size and Assimilate Metabolism-Related Sugars and Enzyme Activities in Giant Pumpkin

Size is the most important quality attribute of giant pumpkin fruit. Different concentrations and application frequencies of α-naphthaleneacetic acid (NAA) and 24-epibrassinolide (EBR) were sprayed on the leaves and fruits of giant pumpkin at different growth stages to determine their effects and the mechanism responsible for fruit size increase. NAA+EBR application improved source strength, and further analysis indicated that NAA+EBR markedly boosted net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (Tr) and the expression level and activity of galactitol synthetase (GolS), raffinose synthetase (RS), and stachyose synthetase (STS), resulting in an increase in the synthesis of photoassimilate, especially stachyose. Concomitantly, NAA+EBR spray increased stachyose and sucrose contents throughout pumpkin fruit growth and the concentrations of glucose and fructose at 0 and 20 days post-anthesis (DPA) in peduncle phloem sap, implying that such treatment improved the efficiency of assimilate transport from the peduncle to the fruit. Furthermore, it improved the expression and activity of alkaline α-galactosidase (AGA), facilitating assimilate unloading, providing carbon skeletons and energy for fruit growth, and increasing fruit weight by more than 44.1%. Therefore, exogenous NAA and EBR increased source capacity, transportation efficiency, and sink strength, overall promoting the synthesis and distribution of photoassimilate, ultimately increasing fruit size.

Inhibition of the Glycogen Synthase Kinase 3 Family by the Bikinin Alleviates the Long-Term Effects of Salinity in Barley

Crops grown under stress conditions show restricted growth and, eventually, reduced yield. Among others, brassinosteroids (BRs) mitigate the effects of stress and improve plant growth. We used two barley cultivars with differing sensitivities to BRs, as determined by the lamina joint inclination test. Barley plants with the 2nd unfolded leaf were sprayed with a diluted series of bikinin, an inhibitor of the Glycogen Synthase Kinase 3 (GSK3) family, which controls the BR signaling pathway. Barley was grown under salt stress conditions up to the start of the 5th leaf growth stage. The phenotypical, molecular, and physiological changes were determined. Our results indicate that the salt tolerance of barley depends on its sensitivity to BRs. We confirmed that barley treatment with bikinin reduced the level of the phosphorylated form of HvBZR1, the activity of which is regulated by GSK3. The use of two barley varieties with different responses to salinity led to the identification of the role of BR signaling in photosynthesis activity. These results suggest that salinity reduces the expression of the genes controlling the BR signaling pathway. Moreover, the results also suggest that the functional analysis of the GSK3 family in stress responses can be a tool for plant breeding in order to improve crops’ resistance to salinity or to other stresses.

Transcriptomic profiling revealed the role of 24-epibrassinolide in alleviating salt stress damage in tall fescue (Festuca arundinacea)

Soil salinization is a major problem all over the world. The accumulation of salt in soil reduces the root water uptake and directly affects plant growth and metabolic activities. Brassinosteroid is a plant hormone that plays an important role in regulation of plant growth and physiological process, including promotion of cell expansion and elongation, signal transduction and stress response. Exogenous 24-epibrassinolide (EBL) has been proved to alleviate various environmental stress in plants. However, the role that EBL plays in salt stress response is still unknown in tall fescue (Festuca arundinacea). In this study, the physiology and molecular mechanisms regulated by exogenous EBL of salt stress response in tall fescue was investigated. Tall fescue plants were divided into four groups, including control (CK), NaCl solution (SALT), 24-epibrassinolide (EBL), NaCl solution + 24-epibrassinolide (SE). During the growth period of tall fescue, we found that electrolyte leakage (EL) and malondialdehyde (MDA) were decreased, chlorophyll (Chl) content and antioxidant enzyme activity were increased in leaves of tall fescue in SE group compared with SALT group, indicating that EBL improved the salt tolerance in grasses. Transcriptomic profiling analysis showed that after 12 h of treatments, 10,265, 13,830 and 10,537 differential genes were expressed in EBL, SALT, and SE groups compared with control, respectively. These differentially expressed genes (DEGs) mainly focused on binding, catalytic activity, cellular process, metabolic process, cellular anatomical entity. Moreover, most of the differential genes were expressed in the plant hormone signal transduction pathway. These results helped us to better understand the mechanism of exogenous 24-epibrassinolide to improve the salt tolerance of tall fescue.

The Mechanisms Underlying Salt Resistance Mediated by Exogenous Application of 24-Epibrassinolide in Peanut

Peanut is one of the most important oil crops in the world, the growth and productivity of which are severely affected by salt stress. 24-epibrassinolide (EBL) plays an important role in stress resistances. However, the roles of exogenous EBL on the salt tolerance of peanut remain unclear. In this study, peanut seedlings treated with 150 mM NaCl and with or without EBL spray were performed to investigate the roles of EBL on salt resistance. Under 150 mM NaCl conditions, foliar application of 0.1 µM EBL increased the activity of catalase and thereby could eliminate reactive oxygen species (ROS). Similarly, EBL application promoted the accumulation of proline and soluble sugar, thus maintaining osmotic balance. Furthermore, foliar EBL spray enhanced the total chlorophyll content and high photosynthesis capacity. Transcriptome analysis showed that under NaCl stress, EBL treatment up-regulated expression levels of genes encoding peroxisomal nicotinamide adenine dinucleotide carrier (PMP34), probable sucrose-phosphate synthase 2 (SPS2) beta-fructofuranosidase (BFRUCT1) and Na⁺/H⁺ antiporters (NHX7 and NHX8), while down-regulated proline dehydrogenase 2 (PRODH). These findings provide valuable resources for salt resistance study in peanut and lay the foundation for using BR to enhance salt tolerance during peanut production.

Development and Comprehensive SPE-UHPLC-MS/MS Analysis Optimization, Comparison, and Evaluation of 2,4-Epibrassinolide in Different Plant Tissues

A determination method for trace 24-epibrassinolide (EBL) in plant tissues was developed using ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The plant tissue samples were extracted using a methanol-formic acid solution, and the corresponding supernatant was purified with ODS C18 solid-phase extraction column. The extracts were separated using a Zorbax Eclipse Plus C18 (2.1 mm × 50 mm, 1.8 μm) column with methanol and 0.1% formic acid as the mobile phase. The ion source for the mass spectrometry was an electrospray ionization source with positive ion mode detection. The linear range of the target compound was 0.7~104 μg/kg, the limit of detection (LOD) was 0.11~0.37 μg/kg, the limit of quantification (LOQ) was 0.36~1.22 μg/kg, the recovery rate was 84.0~116.3%, and the relative standard deviation (RSD%) was 0.8~10.5. The samples of maize plumule, brassica rapeseed flower, and marigold leaf were detected using the external standard method. The optimization of the extraction method and detection method of EBL improved the detection sensitivity, laid a foundation for the artificial synthesis of EBL, improved the extraction rate of EBL, and provided a theoretical basis for the study of EBL in many plants.

Brassinazole Resistant 1 Activity Is Organ-Specific and Genotype-Dependent in Barley Seedlings

Brassinosteroids (BRs) control many plant developmental processes by regulating different groups of transcription factors, and consequently gene expressions. The most known is BZR1, the main member of the BES1 family. However, to date, it is poorly characterized in crop species. The main goal of the presented study was to identify HvBZR1 and determine its activity in 5-day-old barley (the stage is related to one leaf on the main shoot and a few seminal roots) using two cultivars with different sensitivities to BRs. Using the anti-OsBZR1 antibody, we identified the forms of HvBZR1 transcription factor with different molecular weights, which can be related to different phosphorylated forms of serine/threonine residues. Two phosphorylated forms in the shoots and one dephosphorylated form in the roots were determined. A minor amount of the dephosphorylated form of the HvBZR1 in the Haruna Nijo shoots was also found. The phosphorylated forms gave a higher band intensity for Golden Promise than Haruna Nijo. The bands were similar in their intensity, when two different phosphorylated forms were compared in Golden Promise, while a reduced intensity was detected for the phosphorylated form with a lower molecular weight for Haruna Nijo. Degradation of the phosphorylated forms in the shoots (complete degradation in Golden Promise and significant but not complete in Haruna Nijo) and the presence of the dephosphorylated form in the roots were proven for the etiolated barley. In the case of Haruna Nijo, a wider range of the regulators of the BR biosynthesis and signaling pathways induced the expected effects, 24-EBL (0.001 µM) and bikinin (10 and 50 µM) caused low amount of the phosphorylated forms, and at the same time, a tiny band of dephosphorylated form was detected. However, the expression of genes related to the BR biosynthesis and signaling pathways was not a determinant for the protein amount.

24-epibrassinolide confers tolerance against deep-seeding stress in Zea mays L. coleoptile development by phytohormones signaling transduction and their interaction network

Coleoptile/mesocotyl elongation influence seedling emergence and establishment, is major causes of maize deep-seeding tolerance (DST). Detailed analyses on molecular basis underlying their elongation mediated by brassinosteroid under deep-seeding stress (DSS) could provide meaningful information for key factors controlling their elongation. Here we monitored transcriptome and phytohormones changes specifically in elongating coleoptile/mesocotyl in response to DSS and 24-epibrassinolide (EBR)-signaling. Phenotypically, contrasting maize evolved variant organs to positively respond to DST, longer coleoptile/mesocoty of K12/W64A was a desirable organ for seedling under DSS. Applied-EBR improved maize DST, and their coleoptiles/mesocotyls were further elongated. 15,607/20,491 differentially expressed genes (DEGs) were identified in W64A/K12 coleoptile, KEGG analysis showed plant hormone signal transduction, starch and sucrose metabolism, valine, leucine, and isoleucine degradation were critical processes of coleoptile elongation under DSS and EBR signaling, further highly interconnected network maps including 79/142 DEGs for phytohormones were generated. Consistent with these DEGs expression, interactions, and transport, IAA, GA₃, ABA, and Cis-ZT were significantly reduced while EBR, Trans-ZT, JA, and SA were clearly increased in coleoptile under DSS and EBR-signaling. These results enrich our knowledge about the genes and phytohormones regulating coleoptile elongation in maize, and help improve future studies on corresponding genes and develop varieties with DST.

Molecular mechanisms of mesocotyl elongation induced by brassinosteroid in maize under deep-seeding stress by RNA-sequencing, microstructure observation, and physiological metabolism

Deep-seeding is an important way to improve maize drought resistance, mesocotyl elongation can significantly enhance its seedling germination. To improve our understanding of transcription-mediated maize mesocotyl elongation under deep-seeding stress. RNA-sequencing was used to identify differentially expressed genes (DEGs) in both deep-seeding tolerant W64A and intolerant K12 mesocotyls following culture for 10 days after 2.0 mg·L^-1 24-epibrassinolide (EBR) induced stress at the depths of 3 and 20 cm. Phenotypically, the mesocotyl length of both maize significantly increased under 20 cm stress and in the presence of EBR. Microstructure observations revealed that the mesocotyls underwent programmed cell death under deep-seeding stress, which was alleviated by EBR. This was found to be regulated by multiple DEGs encoding cysteine protease/senescence-specific cysteine protease, aspartic protease family protein, phospholipase D, etc. and transcription factors (TFs; MYB, NAC). Additionally, some DEGs associated with cell wall components, i.e., cellulose synthase/cellulose synthase like protein (CESA/CSL), fasciclin-like arabinogalactan (APG), leucine-rich repeat protein (LRR) and lignin biosynthesis enzymes including phenylalanine ammonia-lyase, S-adenosyl-L-methionine-dependent methyltransferases, 4-coumarate-CoA ligase, cinnamoyl CoA reductase, cinnamyl alcohol dehydrogenase, catalase, peroxiredoxin/peroxidase were found to control cell wall sclerosis. Moreover, in auxin, ethylene, brassinosteriod, cytokinin, zeatin, abscisic acid, gibberellin, jasmonic acid, and salicylic acid signaling transduction pathways, the corresponding DEGs were activated/inhibited by TFs (ARF, BZR1/2, B-ARR, A-ARR, MYC2, ABF, TGA) and synthesis of phytohormones-related metabolites. These findings provide information on the molecular mechanisms controlling maize deep-seeding tolerance and will aid in the breeding of deep-seeding maize varieties.

Amelioration of Chlorpyrifos-Induced Toxicity in Brassica juncea L. by Combination of 24-Epibrassinolide and Plant-Growth-Promoting Rhizobacteria

Pervasive use of chlorpyrifos (CP), an organophosphorus pesticide, has been proven to be fatal for plant growth, especially at higher concentrations. CP poisoning leads to growth inhibition, chlorosis, browning of roots and lipid and protein degradation, along with membrane dysfunction and nuclear damage. Plants form a linking bridge between the underground and above-ground communities to escape from the unfavourable conditions. Association with beneficial rhizobacteria promotes the growth and development of the plants. Plant hormones are crucial regulators of basically every aspect of plant development. The growing significance of plant hormones in mediating plant-microbe interactions in stress recovery in plants has been extensively highlighted. Hence, the goal of the current study was to investigate the effect of 24-epibrassinolide (EBL) and PGPRs (Pseudomonas aeruginosa (Ma), Burkholderia gladioli (Mb)) on growth and the antioxidative defence system of CP-stressed Brassica juncea L. seedlings. CP toxicity reduced the germination potential, hypocotyl and radicle development and vigour index, which was maximally recuperated after priming with EBL and Mb. CP-exposed seedlings showed higher levels of superoxide anion (O₂^-), hydrogen peroxide (H₂O₂), lipid peroxidation and electrolyte leakage (EL) and a lower level of nitric oxide (NO). In-vivo visualisation of CP-stressed seedlings using a light and fluorescent microscope also revealed the increase in O₂^-, H₂O₂ and lipid peroxidation, and decreased NO levels. The combination of EBL and PGPRs reduced the reactive oxygen species (ROS) and malondialdehyde (MDA) contents and improved the NO level. In CP-stressed seedlings, increased gene expression of defence enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APOX), glutathione peroxidase (GPOX), dehydroascorbate reductase (DHAR) and glutathione reductase (GPOX) was seen, with the exception of catalase (CAT) on supplementation with EBL and PGPRs. The activity of nitrate reductase (NR) was likewise shown to increase after treatment with EBL and PGPRs. The results obtained from the present study substantiate sufficient evidence regarding the positive association of EBL and PGPRs in amelioration of CP-induced oxidative stress in Brassica juncea seedlings by strengthening the antioxidative defence machinery.

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.

24-epibrassinolide-induced growth promotion of wheat seedlings is associated with changes in the proteome and tyrosine phosphoproteome

Brassinosteroids (BRs) represent a unique class of steroidal plant hormones that display pronounced growth-promoting activity at very low concentrations. Although many efforts have been made to characterize the molecular basis of BR action, little is known about the mechanisms behind the growth-promoting effect of BRs at protein level. Proteomic analysis of response to the steroid plant hormone 24-epibrassinolide (EBR) in wheat seedling shoots (Triticum aestivum L.) was performed using two-dimensional electrophoresis (2-DE) and immunoblotting with highly specific antibodies (PY20) to phosphotyrosine. EBR-modulated proteins and phosphotyrosine polypeptides were identified using MALDI-TOF mass spectrometry. The study revealed that EBR-stimulated growth of wheat seedlings was accompanied by changes in the content of multiple proteins as well as in tyrosine phosphorylation of numerous polypeptides. Among them, 22 differentially accumulated proteins and 13 phosphotyrosine proteins were identified. Based on their performed functions, the identified proteins are involved in physiological processes (photosynthesis, growth, energy and amino acid metabolism) closely associated with intensification of plant metabolism. The EBR-induced changes in protein abundance and tyrosine phosphorylation profile may contribute to growth stimulation of wheat seedlings under the action of EBR. The obtained data suggest an important role for EBR in the activation of protein metabolism underlying fundamental physiological processes, including growth promotion.

Exogenous 24-epibrassinolide activates detoxification enzymes to promote degradation of boscalid in cherry tomatoes

BACKGROUND

Boscalid is often used to extend the storage time of postharvest cherry tomato. Pesticide residue has become an issue of food safety. This study sought to investigate the spatial distribution of boscalid residue in cherry tomato fruits and to determine the effect of 24-epibrassinolide (EBR) in promoting boscalid degradation.

RESULTS

Boscalid could quickly penetrate into cherry tomatoes, but mainly remained in the peel. The migration of boscalid from the peel into the core was a time-consuming and complex process during storage. After 72 h, boscalid residues in the pulp and the core began to accumulate gradually. The exogenous application of EBR activated peroxidase, glutathione reductase and glutathione S-transferase, and effectively promoted the degradation of boscalid by a maximum decrease of 44.8% in peel, 54.0% in pulp and 71.2% in core.

CONCLUSION

As one of the common pesticides, boscalid had a strong ability to enter the cherry tomato and thus become a potential risk for public consumption. Therefore, rational use of pesticides is recommended. The results of this study indicate that the possible risk of boscalid residue could be alleviated by EBR pretreatment through activating detoxification enzymes. © 2020 Society of Chemical Industry.

A defect in BRI1-EMS-SUPPRESSOR 1 (bes1)-mediated brassinosteroid signaling increases photoinhibition and photo-oxidative stress during heat stress in Arabidopsis

Heat stress has negative effects on plant performance, especially in photosynthesis and photoprotection. To withstand heat stress, plants modulate steroid phytohormones, brassinosteroids (BRs). However, their regulation and functions in heat stress acclimation are still poorly understood. Plant growth, photoinhibition, photo-oxidative stress and endogenous contents of hormones (including not only BRs but also abscisic acid, salicylic acid and jasmonic acid) were evaluated during heat stress in Arabidopsis thaliana wild type plants and loss-of-function mutations in either BR biosynthetic or signaling genes. It was found that a defect in BRI1-EMS-SUPPRESSOR 1 (bes1)-mediated BR signaling showed the most sensitive characteristics to heat stress compared to wild type and other BR mutants. Sensitivity was associated with declined PSII photochemistry efficiency (F_v/F_m) together with increased carotenoid, tocopherol and lipid hydroperoxide contents, which evidences higher photoinhibition and photo-oxidative stress in the bes1 mutant under heat stress. Furthermore, the bes1 mutant showed greater contents of abscisic acid (ABA) after one day of exposure to heat stress. However, all heat stress symptoms in the bes1 mutant could be mitigated by the application of 24-epibrassinolide. Therefore, it is concluded that BES1 transcription factor plays a role in plants responses to heat stress, relieving photoinhibition and photo-oxidative stress, but that alternative BR signaling pathways to BES1 may also be effective in heat stress acclimation. Furthermore, this study emphasizes the complex interplay between BR and ABA in the heat acclimation process.

24-Epibrassinolide (EBR) Confers Tolerance against NaCl Stress in Soybean Plants by Up-Regulating Antioxidant System, Ascorbate-Glutathione Cycle, and Glyoxalase System

: The present research was performed to assess the effect of 24-epibrassinolide (EBR) on salt-stressed soybean plants. Salt stress suppressed growth, biomass yield, gas exchange parameters, pigment content, and chlorophyll fluorescence, but all these parameters were up-regulated by EBR supply. Moreover, salt stress increased hydrogen peroxide, malondialdehyde, and electrolyte leakage. EBR supplementation reduced the accumulation of oxidative stress biomarkers. The activities of superoxide dismutase and catalase, and the accumulation of proline, glycinebetaine, total phenols, and total flavonoids increased with NaCl stress, but these attributes further increased with EBR supplementation. The activities of enzymes and the levels of non-enzymatic antioxidants involved in the Asc-Glu cycle also increased with NaCl stress, and further enhancement in these attributes was recorded by EBR supplementation. Salinity elevated the methylglyoxal content, but it was decreased by the EBR supplementation accompanying with up-regulation of the glyoxalase cycle (GlyI and GlyII). Salinity enhanced the Na+ uptake in root and shoot coupled with a decrease in uptake of Ca2+, K+, and P. However, EBR supplementation declined Na+ accumulation and promoted the uptake of the aforementioned nutrients. Overall, EBR supplementation regulated the salt tolerance mechanism in soybean plants by modulating osmolytes, activities of key enzymes, and the levels of non-enzymatic antioxidants.

24-epibrassinolide application enhances growth and biochemical aspects of squash under salt stress conditions

Brassinosteroids (BRs) are considered to possess protective activity in plants exposed to various stresses. The present study was conducted to evaluate the effects of 24-epibrassinolide (EBL) on salt stressed summer squash cv. Eskandrani seedlings, whether it can alleviate the deleterious effects of salt stress in growing seedlings or not. For this, summer squash seeds were germinated in solidified half strength MS (Murashige and Skoog) medium supplemented with different concentrations and combinations of EBL (0, 5, 10 and 20 μM) and NaCl (0, 50, 100 and 150 mM). The different concentrations (5, 10, 20 μM) of EBL significantly increased germination percentage and seedling growth capacity and the greatest increase was observed at 10 μM EBL. EBL application significantly increased the contents of photosynthetic pigments, the relative water content and the uptake of K and Ca. However, the different concentrations (50, 100 and 150 mM) of NaCl significantly decreased the above-mentioned attributes. The different concentrations (50, 100 and 150 mM) of NaCl significantly increased the electrolyte leakage, the lipid peroxidation and the Na uptake, but the interaction between EBL and NaCl significantly decreased these parameters. The results of this study proved that the application of 24-epibrassinolide to growing squash seedlings under salt stress conditions reduced the deleterious effects of salt stress and increased the tolerance of seedlings to its detrimental effects.

Transcriptomic profiling of tall fescue in response to heat stress and improved thermotolerance by melatonin and 24-epibrassinolide

Background

Tall fescue is a widely used cool season turfgrass and relatively sensitive to high temperature. Chemical compounds like melatonin (MT) and 24-epibrassinolide (EBL) have been reported to improve plant heat stress tolerance effectively.

Results

In this study, we reported that MT and EBL pretreated tall fescue seedlings showed decreased reactive oxygen species (ROS), electrolyte leakage (EL) and malondialdehide (MDA), but increased chlorophyll (Chl), total protein and antioxidant enzyme activities under heat stress condition, resulting in improved plant growth. Transcriptomic profiling analysis showed that 4311 and 8395 unigenes were significantly changed after 2 h and 12 h of heat treatments, respectively. Among them, genes involved in heat stress responses, DNA, RNA and protein degradation, redox, energy metabolisms, and hormone metabolism pathways were highly induced after heat stress. Genes including FaHSFA3, FaAWPM and FaCYTC2 were significantly upregulated by both MT and EBL treatments, indicating that these genes might function as the putative target genes of MT and EBL.

Conclusions

These findings indicated that heat stress caused extensively transcriptomic reprogramming of tall fescue and exogenous application of MT and EBL effectively improved thermotolerance in tall fescue.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-4588-y) contains supplementary material, which is available to authorized users.

Transcriptional Regulation of Brassinosteroid Accumulation during Carrot Development and the Potential Role of Brassinosteroids in Petiole Elongation

It is widely known that brassinosteroids (BRs) are involved in various physiological processes during plant growth and development. Roles of BRs have been reported in many plants. However, relevant report is yet not found in carrot. Carrot is a nutrient-rich vegetable from the Apiaceae family. Here, we measured the bioactive contents of BRs at five successive stages and analyzed the expression profiles of genes involved in BR biosynthesis, signaling pathway and catabolism. We found that most biosynthesis regulated genes had higher expression level at the first development stage of carrot and the catabolism gene BAS1/CYP734A1 had significantly high expression level at the first stage in carrot roots and petioles. In addition, we treated carrot plants with exogenous 24-epibrassinolide (24-EBL) and examined the morphological changes after treating. Compared with control plants, carrot plants treated with 24-EBL had higher plant height, more number of petioles and heavier aboveground weight. The expression levels of DcBRI1, DcBZR1, and DcBSU1 in the petioles were significantly up-regulated by treating with exogenous 24-EBL. The expression profiles of DcCYP734A1 were all significantly up-regulated in the three organs when treated with 0.5 mg/L 24-EBL. The elongation of carrot petioles can be promoted by treating with exogenous 24-EBL. These results indicate that BRs playing potential roles during the growth and development of carrot.

Physiological Mechanism of Enhancing Salt Stress Tolerance of Perennial Ryegrass by 24-Epibrassinolide

Brassinosteroids (BR) regulate plant tolerance to salt stress but the mechanisms underlying are not fully understood. This study was to investigate physiological mechanisms of 24-epibrassinolide (EBR)'s impact on salt stress tolerance in perennial ryegrass (Lolium perenne L.) The grass seedlings were treated with EBR at 0, 10, and 100 nM, and subjected to salt stress (250 mM NaCl). The grass irrigated with regular water without EBR served as the control. Salt stress increased leaf electrolyte leakage (EL), malondialdehyde (MDA), and reduced photosynthetic rate (Pn). Exogenous EBR reduced EL and MDA, increased Pn, chlorophyll content, and stomatal conductance (gs). The EBR applications also alleviated decline of superoxide dismutase (SOD) and catalase (CAT) and ascorbate peroxidase (APX) activity when compared to salt treatment alone. Salt stress increased leaf abscisic acid (ABA) and gibberellin A4 (GA4) content but reduced indole-3-acetic acid (IAA), zeatin riboside (ZR), isopentenyl adenosine (iPA), and salicylic acid (SA). Exogenous EBR at 10 nm and 100 nM increased ABA, and iPA content under salt stress. The EBR treatment at 100 nM also increased leaf IAA, ZR, JA, and SA. In addition, EBR treatments increased leaf proline and ions (K+, Mg2+, and Ca2+) content, and reduced Na+/K+ in leaf tissues. The results of this study suggest that EBR treatment may improve salt stress tolerance by increasing the level of selected hormones and antioxidant enzyme (SOD and CAT) activity, promoting accumulation of proline and ions (K+, Ca2+, and Mg2+) in perennial ryegrass.

Effect of seed pre-soaking with 24-epibrassinolide on growth and photosynthetic parameters of Brassica juncea L. in imidacloprid soil

Pesticides are widely used to protect crop plants from various insect pests. However, application of pesticides causes phytotoxicity to plants which results in their impaired growth and development. Brassinosteroids are well known to protect plants under abiotic stress conditions. The purpose of the present study was to access the ameliorative role of 24-epibrassinolide (EBR) in Brassica juncea L. under imidacloprid (IMI) toxicity. B. juncea plants were raised from seeds soaked in 0.1, 1 and 100nM of EBR, and grown in soils amended with 250, 300 and 350mgkg(-1) IMI pesticide, and observed for growth, pigments and photosynthetic parameters after 30, 60 and 90 days of seed sowing. The plants grown in soil treated with IMI exhibited a significant reduction in shoot length, number of leaves, chlorophyll contents and photosynthetic parameters like photosynthetic rate, stomatal conductance, inter-cellular CO2 and transpiration rate, when compared with their respective controls. However, pigments which act as antioxidants such as carotenoids, anthocyanins and xanthophylls were increased with IMI stress. Pre-sowing seed treatment with EBR decreased the toxic effects of IMI and increased the growth, pigment biosynthesis and photosynthetic parameters of the plants grown in IMI amended soil. Maximum increase in all the growth and photosynthetic parameters was noticed in plants raised from seeds treated with 100nM EBR and grown in IMI amended soil.

[Combined effects of 24-epibrassinolide and salinity on the growth and physiological perfor-mance of Ulva prolifera]

In order to study the combined effects of brassinosteroids and salinity on the growth and physiological performance of Ulva prolifera under low temperature condition, we investigated the growth, chlorophyll content, chlorophyll fluorescence parameters, soluble protein and carbohydrate contents in this algae, which was grown under three salinity in the presence or absence of 24-epibrassinolide. The results showed that, compared to control salinity (25) treatment, the growth rate of U. prolifera was enhanced by 45.9% under the moderate hyposaline condition (10), but decreased under low salinity (5) treatment, which showed high contents of chlorophyll and soluble protein. However, the presence of EBR (0.2 mg·L^-1) significantly reduced the growth of U. prolifera, especially under the control salinity (25) treatment, under which the fresh mass decreased and more spores were released. Additionally, the effective quantum yield (F_v'/F_m'), the activity of SOD and the content of soluble carbohydrate also decreased, but the soluble protein content increased under the control salinity treatment in the presence of EBR. In conclusion, moderatehypo-saline condition could be used to enhance the growth of U. prolifera at 15 ℃, and under normal salinity (25), the EBR could be used to promote the release of spores and produce more materials for mass production of U. prolifera.

Brassinosteroids Improve Quality of Summer Tea (Camellia sinensis L.) by Balancing Biosynthesis of Polyphenols and Amino Acids

Summer grown green tea is less popular due to bitterness and high astringency, which are attributed to high levels of tea polyphenols (TP) and low levels of amino acids (AA) in tea leaves (Camellia sinensis L.). Brassinosteroids (BRs), a group of steroidal plant hormones can regulate primary and secondary metabolism in a range of plant species under both normal and stress conditions. However, specific effects of BRs on the photosynthesis of tea plants and the quality of summer green tea are largely unknown. Here we show that 24-epibrassinolide (EBR), a bioactive BR, promoted photosynthesis in tea plants in a concentration-dependent manner. Stimulation in photosynthesis by EBR resulted in an increased summer tea yield. Although all tested concentrations (0.01, 0.05, 0.1, 0.5, and 1.0 ppm) of EBR increased concentrations of TP and AA, a moderate concentration (0.5 ppm) caused the highest decrease in TP to AA ratio, an important feature of quality tea. Time-course analysis using 0.5 ppm EBR as foliar spray revealed that TP or AA concentration increased as early as 3 h after EBR application, reaching the highest peak at 24 h and that remained more or less stable. Importantly, such changes in TP and AA concentration by EBR resulted in a remarkably decreased but stable TP to AA ratio at 24 h and onward. Furthermore, concentrations of catechins and theanine increased, while that of caffeine remained unaltered following treatment with EBR. EBR improved activity of phenylalanine ammonia-lyase (PAL) and glutamine: 2-oxoglutarate aminotransferase (GOGAT) enzymes involved in catechins and theanine biosynthesis, respectively. Transcript analysis revealed that transcript levels of CsPAL and CsGS peaked as early as 6 h, while that of CsGOGAT peaked at 12 h following application of EBR, implying that EBR increased the concentration of TP and AA by inducing their biosynthesis. These results suggest a positive role of BR in enhancing green tea quality, which might have potential implication in improving quality of summer tea.

Synergistic effect of auxins and brassinosteroids on the growth and regulation of metabolite content in the green alga Chlorella vulgaris (Trebouxiophyceae)

The relationships between brassinosteroids (BRs) (brassinolide, BL; 24-epiBL; 28-homoBL; castasterone, CS; 24-epiCS; 28-homoCS) and auxins (indole-3-acetic acid, IAA; indole-3-butyric acid, IBA; indole-3-propionic acid, IPA) in the regulation of cell number, phytohormone level and metabolism in green alga Chlorella vulgaris were investigated. Exogenously applied auxins had the highest biological activity in algal cells at 50 μM. Among the auxins, IAA was characterized by the highest activity, while IBA - by the lowest. BRs at 0.01 μM were characterized by the highest biological activity in relation to auxin-treated and untreated cultures of C. vulgaris. The application of 50 μM IAA stimulated the level of all detected endogenous BRs in C. vulgaris cells. The stimulatory effect of BRs in green algae was arranged in the following order: BL > 24-epiBL > 28-homoBL > CS > 24-epiCS > 28-homoCS. Auxins cooperated synergistically with BRs stimulating algal cell proliferation and endogenous accumulation of proteins, chlorophylls and monosaccharides in C. vulgaris. The highest stimulation of algal growth and the contents of analyzed biochemical parameters were observed for the mixture of BL with IAA, whereas the lowest in the culture treated with both 28-homoCS and IBA. However, regardless of the applied mixture of BRs with auxins, the considerable increase in cell number and the metabolite accumulation was found above the level obtained in cultures treated with any single phytohormone. Obtained results confirm that both groups of plant hormones cooperate synergistically in the control of growth and metabolism of unicellular green alga C. vulgaris.

24-epibrassinolide induced antioxidative defense system of Brassica juncea L. under Zn metal stress

The present study deals with the effects of 24-epibrassinolide on growth, lipid peroxidation, antioxidative enzyme activities, non-enzymatic antioxidants and protein content in 30 days old leaves of Brassica juncea (var. PBR 91) under zinc metal stress in field conditions. Surface sterilized seeds of B. juncea were given pre-soaking treatments of 24-EBL (10(-10), 10(-8) and 10(-6) M) for 8 h. Different concentrations of zinc metal in the form of ZnSO4.7H2O (0, 0.5, 1.0, 1.5 and 2.0 mM) were added in the soil kept in experimental pots. Seeds soaked in 24-EBL for 8 h were sown in the earthern pots containing different concentrations of Zn metal. After 30 days of sowing, the plants were analyzed for growth parameters in terms of shoot length and number of leaves. Thereafter, leaves were excised and content of proteins, non-enzymatic antioxidants, malondialdehyde (MDA) and the activities of antioxidative enzymes (superoxide dismutase (SOD) (EC 1.15.1.1) catalase (CAT) (EC 1.11.1.6), ascorbate peroxidase (APOX) (EC 1.11.1.11), guaiacol peroxidase (POD) (EC 1.11.1.7) glutathione reductase (GR) (EC 1.6.4.2), monodehydroascorbate reductase (MDHAR) (EC 1.1.5.4) and dehydroascorbate reductase (DHAR) (EC 1.8.5.1)) were analyzed. It was observed that the growth of plants was inhibited under Zn metal stress. However, 24-EBL seed-presoaking treatment improved the plant growth in terms of increase in shoot length. 24-EBL also mitigated the toxicity of Zn metal by increasing the number of leaves. The activities of antioxidative enzymes (SOD, CAT, POD, GR, APOX, MDHAR and DHAR) and contents of proteins and glutathione were also enhanced in leaves of plants treated with 24-EBL alone, 10(-8) M concentration being the most effective. The activities of antioxidative enzymes also increased in leaves of B. juncea plants by the application 24-EBL supplemented Zn metal solutions. Similarly, the content of proteins and glutathione increased considerably in leaves of B. juncea plants treated with 24-EBL, whereas the level of MDA content decreased in 24-EBL treated plants as compared to untreated control plants thereby revealing stress-protective properties of the brassinolide.