Brassinolide as potential rescue agent for Pinellia ternata grown under microplastic condition: Insights into their modulatory role on photosynthesis, redox homeostasis, and AsA-GSH cycling

Microplastic (MP), as a new pollutant, not only affects the growth and development of plants but also may affect the secondary metabolites of plants. The anti-tumor role of Pinellia ternata is related to secondary metabolites. The role of brassinolide (BR) in regulating plant resistance is currently one of the research hotspots. The paper mainly explores the regulation of BR on growth and physiology of Pinellia ternata under MP stress. The experimental design includes two levels of MP (0, 1%) and two levels of BR (0, 0.1 mg/L). MP led to a marked reduction in plant height (15.0%), Fv/Fm (3.2%), SOD and APX activity (15.0%, 5.1%), whereas induced an evident raise in the rate of O2·- production (29.6%) and GSH content (4.4%), as well as flavonoids (6.8%), alkaloids (75%), and β-sitosterol (26.5%) contents. Under MP addition, BR supply significantly increased plant height (15.7%), aboveground and underground biomass (16.1%, 10.3%), carotenoid and GSH content (11.8%, 4.2%), Fv/Fm (2.9%), and activities of SOD, GR, and MDHAR (32.2%, 21.08%, 20.9%). These results indicate that MP suppresses the growth of P. ternata, although it promotes secondary metabolism. BR can alleviate the inhibitory effect of MP on growth by improving photosynthesis, redox homeostasis, and the AsA-GSH cycle.

Sodium nitrophenolate mediates brassinosteroids signaling to enhance cold tolerance of cucumber seedling

Cold stress (CS) significantly limits cucumber yield. However, it remains unclear whether and how sodium nitrophenolate (CSN) regulates plant responses to cold stress. Here, H2O, CSN, 24-epibrassinolide (EBR), and CSN + EBR were sprayed on cucumber seedlings before or after CS, and on control plants. We found that CSN, EBR, or EBR + CSN pre-treatment improved seedling growth under normal conditions (control condition) and cold tolerance under CS conditions. EBR pre-treatment promoted the expression of approximately half of the genes involved in BR synthesis and signaling and CsICE-CsCBF-CsCOR under CS. However, CSN pre-treatment promoted almost all the expression of BR synthesis and signaling genes, and CsICE-CsCBF-CsCOR genes, which showed the highest expression in early CS, remarkably improving the cold tolerance of cucumber. Interestingly, EBR and CSN had a superimposed effect on the expression of BR synthesis and signaling and CsICE-CsCBF-CsCOR genes, which rapidly increased their expression under normal temperature. Spraying EBR after CS accelerated seedling recovery, whereas CSN had the opposite effect. However, spraying CSN combined with EBR accelerated the recovery of CS-injured seedlings and was better than spraying EBR alone. Although CS-injured seedlings were negatively influenced by CSN, pre-treatment with CSN accelerated seedling growth and increased cold tolerance, suggesting that the effect of CSN was related to whether the seedlings were damaged by CS. In conclusion, we firstly found that CSN enhanced cold tolerance by activating BR signaling, contributing to the gene expression of ICE-CBF-COR and that CSN + EBR contributed to cold tolerance and CS-injured seedling recovery in cucumber.

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.

Anti-cancer activity, and molecular docking of novel hybrid heterocyclic steroids revealed promising anti-hepatocellular carcinoma agent: Implication of cyclin dependent kinase-2 pathway

To identify new steroidal agents with potential biological activities, we synthesized hybrid steroids containing thiazole, pyrazole, isoxazole, thiophene or phthalazine moiety. Epi-androsterone 1 reacted with phenylthiosemicarbazide to afford the corresponding androstane-4-phenyl-3-thiosemicarbazone derivative 2. The latter product was used in the synthesis of a series of annulated steroid derivatives. Also, Epi-androsterone 1 reacted with the thienopyridazine derivative 16 to afford the thieno[3,4-d]pyridazino-N-ylidenoandrostane derivative 17. Compound 17 reacted readily with electron-poor olefins to yield the corresponding phthalazine steroid derivatives. Detailed experimental and spectroscopic evidences for the structures of the newly synthesized compounds are explained. Compounds 3, 7, 8a, 12a, 14, 17 and 21a, were investigated individually as anticancer agents on different panel of human malignant cell lines. Moreover, a computer modelling investigation was performed to speculate the macromolecular targets for the most promising candidate. The results revealed a concentration-dependent reduction in the number of viable cells in all cancer cell lines. Most notably, compound 7 was the most effective compound against all tested cancer cell lines, especially against HepG2 cell line; therefore, the mode of action of this compound against HCC was investigated. Compound 7 was able to induce cell cycle arrest, and DNA fragmentation in HepG2 cells. Moreover, compound 7 induced apoptosis via upregulating the expression of caspase-3, -8, -9, P53, Bax and inhibiting the expression of BCL2, and CDK2 genes. Our results highlighted compound 7 as a promising anti-hepatocellular carcinoma agent, with theoretical, and practical potential binding affinity with CDK2; therefore, more investigations are required to elucidate its chemotherapeutic value as anti-HCC agent.

Formation of nitrogen-containing six-membered heterocycles on steroidal ring system: A review

Steroidal heterocyclic compounds constitute interesting and promising scaffolds for drug discovery as they have displayed diverse chemical reactivity and several types of biological activities. This study is a concise report on the most recent advancements in the chemistry of the steroid skeleton, including reactions at the A, B, and D ring systems. The modern synthetic methods for the steroidal nitrogen-containing six-membered heterocyclic derivatives from 3-keto-, 6-keto-, 17-keto-, and 20-keto-steroids, as well as 2-Aldo-, 4-Aldo-, 6-Aldo-, and 16-Aldo-steroids, are discussed. However, some other methods for the synthesis of steroidal N-containing 6-membered heterocyclic derivatives are also included. These compounds have shown therapeutic potential as cytotoxic agents against various cell lines and have also shown antiproliferative, anti-inflammatory, and antioxidant activities. Therefore, they could be used as prospective candidates for the development of various medications. This paper not only describes synthetic details involved in creating N-containing 6-membered heterocyclic steroid derivatives, but also provides a brief overview of the medicinal applications of these compounds. This information will be highly useful for the medicinal chemists conducting research in this field.

Cancer and brassinosteroids: Mechanisms of action, SAR and future perspectives

Brassinosteroids are plant hormones whose main function is to stimulate plant growth. However, they have been studied for their biological applications in humans. Brassinosteroid compounds have displayed an important role in the study of cancer pathology and show potential for developing novel anticancer drugs. In this review we describe the relationship of brassinosteroids with cancer with focus on the last decade, the mechanisms of cytotoxic activity described to date, and a structure-activity relationship based on the available information.

Brassinolide alleviates Fe deficiency-induced stress by regulating the Fe absorption mechanism in Malus hupehensis Rehd

Exogenous brassinolide promotes Fe absorption through mechanism I strategy, thus improving the tolerance of Malus hupehensis seedlings to Fe deficiency stress. Iron (Fe) deficiency is a common nutritional disorder that results in decreased yield and poor fruit quality in apple production. As a highly active synthetic analog of brassinosteroids, brassinolide (BL) plays numerous roles in plant responses to abiotic stresses. However, its role in Fe deficiency stress in apple plants has never been reported. Herein, we found that the exogenous application of 0.2 mg L^-1 BL could significantly enhance the tolerance of apple seedlings to Fe deficiency stress and result in a low etiolation rate and a high photosynthetic rate. The functional mechanisms of this effect were also explored. We found that first, exogenous BL could improve Fe absorption through the mechanism I strategy. BL induced the activity of H⁺-ATPase and the expression of MhAHA family genes, resulting in rhizosphere acidification. Moreover, BL could enhance the activity of Fe chelate reductase and absorb Fe through direct binding with the E-box of the MhIRT1 or MhFRO2 promoter via the transcription factors MhBZR1 and MhBZR2. Second, exogenous BL alleviated osmotic stress by increasing the contents of osmolytes (proline, solution proteins, and solution sugar) and scavenged reactive oxygen species by improving the activities of antioxidant enzymes. Lastly, exogenous BL could cooperate with other endogenous plant hormones, such as indole-3-acetic acid, isopentenyl adenosine, and gibberellic acid 4, that respond to Fe deficiency stress indirectly. This work provided a theoretical basis for the application of exogenous BL to alleviate Fe deficiency stress in apple plants.

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.

24-Epibrassinolide modulates the neurodevelopmental outcomes of high caffeine exposure in zebrafish (Danio rerio) embryos

Previous embryonic fish data have shown caffeine to induce potential teratogenic and long-term neurodevelopmental outcomes through oxidative stress-mediated apoptosis. In this context, antioxidants may have the potential to counteract the caffeine-induced effects. Therefore, the present study aimed to investigate the potential protective role of 24-epibrassinolide (24-EPI), a natural brassinosteroid with proven antioxidant properties, against caffeine-induced teratogenic effects during early zebrafish development. Embryos (~2 h post-fertilization - hpf) were exposed to 0.5 mM caffeine, co-exposed to 24-EPI (0.01, 0.1 and 1 μM) and to 24-EPI alone (1 μM) for 96 h. During exposure, lethal and sublethal developmental parameters were evaluated. At the end of the exposure, biochemical evaluations were made, and 24 h after, different behavioural paradigms were assessed. An increased number of animals showing oedema and malformations were observed after caffeine exposure, while these were reduced after co-exposure to 24-EPI concentration, namely the tail curvature. The results showed oxidative stress and related parameters similar among treatments. Yet, caffeine exposure resulted in locomotor deficits (decreased speed and distance) and disrupted anxiety-like and avoidance responses. The co-exposure to caffeine and to the highest 24-EPI concentrations resulted in less pronounced behavioural deficits. Overall, there was an absence of effects in the embryo/larvae exposed solely to 24-EPI, while caffeine caused developmental and neurotoxic effects. Although further studies are needed, the results showed promising protective effects of the highest 24-EPI concentration tested against the toxicity induced by caffeine in zebrafish.

Brassinosteroids Influence Arabidopsis Hypocotyl Graviresponses through Changes in Mannans and Cellulose

The force of gravity is a constant environmental factor. Plant shoots respond to gravity through negative gravitropism and gravity resistance. These responses are essential for plants to direct the growth of aerial organs away from the soil surface after germination and to keep an upright posture above ground. We took advantage of the effect of brassinosteroids (BRs) on the two types of graviresponses in Arabidopsis thaliana hypocotyls to disentangle functions of cell wall polymers during etiolated shoot growth. The ability of etiolated Arabidopsis seedlings to grow upward was suppressed in the presence of 24-epibrassinolide (EBL) but enhanced in the presence of brassinazole (BRZ), an inhibitor of BR biosynthesis. These effects were accompanied by changes in cell wall mechanics and composition. Cell wall biochemical analyses, confocal microscopy of the cellulose-specific pontamine S4B dye and cellular growth analyses revealed that the EBL and BRZ treatments correlated with changes in cellulose fibre organization, cell expansion at the hypocotyl base and mannan content. Indeed, a longitudinal reorientation of cellulose fibres and growth inhibition at the base of hypocotyls supported their upright posture whereas the presence of mannans reduced gravitropic bending. The negative effect of mannans on gravitropism is a new function for this class of hemicelluloses. We also found that EBL interferes with upright growth of hypocotyls through their uneven thickening at the base.

Epibrassinolide improves the growth performance of Sedum lineare upon Zn stress through boosting antioxidative capacities

As an essential element, zinc (Zn) can improve or inhibit the growth of plants depending on its concentrations. In this study, the effects of 24-Epibrassinolide (EBR), one well-known steroid phytohormone regulating plant growth and alleviating abiotic stress damage, on morphological parameters and antioxidant capacities of Sedum lineare were investigated under different Zn doses. Compared to plants only exposed to Zn, simultaneously foliar application of 0.75 μM EBR significantly improved multiple morphological characteristics and such growth-improving effects were more significant at high Zn concentrations. At a detrimental 800 μM Zn, EBR benefitted plant growth most prominently, as shown by that the stem length, fresh weight and internode length were increased by 111%, 85% and 157%, respectively; than Zn solely treated plants. EBR spray also enhanced both the activities of antioxidant enzymes such as peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), and the contents of antioxidative agents including ascorbic acid (AsA) and glutathione (GSH), which in turn decreased the accumulation of reactive oxygen species (ROS) and alleviated the lipid peroxidation in plants. Thus, by demonstrating that EBR could help S. lineare resist high-zinc stress through strengthening the antioxidant system, this work provided a new idea for expanding the planting range of Crassulaceae plants in heavy metal contaminated soil for phytoremediation purpose in the future.

Leaf application of 24-epibrassinolide mitigates cadmium toxicity in young Eucalyptus urophylla plants by modulating leaf anatomy and gas exchange

Cadmium (Cd2+) soil pollution is a global environmental problem caused by the high toxicity of Cd. 24-Epibrassinolide (EBR) is a biodegradable plant steroid involved in response modulation to biotic and abiotic stresses. The aim of this study was to evaluate if the leaf-application of EBR improves the gas exchange and possible repercussions on leaf anatomy in young Eucalyptus urophylla plants exposed to Cd toxicity. The experiment involved six treatments, which included three Cd concentrations (0, 450, and 900 μM) and two EBR concentrations (0 and 100 nM, described as - EBR and + EBR, respectively). Plants exposed to Cd toxicity suffered decreases in leaf anatomical and gas exchange parameters. However, the plants treated with EBR + 900 μM Cd showed an increase of 46%, 40%, and 54% in the net photosynthetic rate, water-use efficiency, and instantaneous carboxylation efficiency, respectively. The EBR application-induced improvements in gas exchange parameters, causing beneficial effects on the photosynthetic apparatus, mainly the effective quantum yield of photosystem II (PSII) photochemistry and electron transport rate. Furthermore, this steroid mitigated the effect of Cd toxicity on leaf anatomical variables, more specifically palisade and spongy parenchyma, which are intrinsically related to stomatal density, and stimulated the net photosynthetic rate of plants.

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.

Genome-Wide Identification of the B-BOX Genes that Respond to Multiple Ripening Related Signals in Sweet Cherry Fruit

B-BOX proteins are zinc finger transcription factors that play important roles in plant growth, development, and abiotic stress responses. In this study, we identified 15 PavBBX genes in the genome database of sweet cherry. We systematically analyzed the gene structures, clustering characteristics, and expression patterns of these genes during fruit development and in response to light and various hormones. The PavBBX genes were divided into five subgroups. The promoter regions of the PavBBX genes contain cis-acting elements related to plant development, hormones, and stress. qRT-PCR revealed five upregulated and eight downregulated PavBBX genes during fruit development. In addition, PavBBX6, PavBBX9, and PavBBX11 were upregulated in response to light induction. We also found that ABA, BR, and GA₃ contents significantly increased in response to light induction. Furthermore, the expression of several PavBBX genes was highly correlated with the expression of anthocyanin biosynthesis genes, light-responsive genes, and genes that function in multiple hormone signaling pathways. Some PavBBX genes were strongly induced by ABA, GA, and BR treatment. Notably, PavBBX6 and PavBBX9 responded to all three hormones. Taken together, BBX proteins likely play major roles in regulating anthocyanin biosynthesis in sweet cherry fruit by integrating light, ABA, GA, and BR signaling pathways.

Transcriptomic analyses show that 24-epibrassinolide (EBR) promotes cold tolerance in cotton seedlings

In plants, brassinosteroids (BRs) are a class of steroidal hormones that are involved in numerous physiological responses. However, the function of BRs in cold tolerance in cotton has not been explored. In this study, cotton seedlings were treated with five concentrations (0, 0.05, 0.1, 0.2, 0.5 and 1.0 mg/L) of 24-Epibrassinolide (EBR) at 4°C. We measured the electrolyte leakage, malondialdehyde (MDA) content, proline content, and net photosynthesis rate (Pn) of the seedlings, which showed that EBR treatment increased cold tolerance in cotton in a dose-dependent manner, and that 0.2 mg/L is an optimum concentration for enhancing cold tolerance. The function of EBR in cotton cotyledons was investigated in the control 0 mg/L (Cold+water) and 0.2 mg/L (Cold+EBR) treatments using RNA-Seq. A total of 4,001 differentially expressed genes (DEGs), including 2,591 up-regulated genes and 1,409 down-regulated genes were identified. Gene Ontology (GO) and biochemical pathway enrichment analyses showed that EBR is involved in the genetic information process, secondary metabolism, and also inhibits abscisic acid (ABA) and ethylene (ETH) signal transduction. In this study, physiological experiments showed that EBR can increase cold tolerance in cotton seedlings, and the comprehensive RNA-seq data shed light on the mechanisms through which EBR increases cold tolerance in cotton seedlings.

24-Epibrassinolide alleviates the toxic effects of NaCl on photosynthetic processes in potato plants

Brassinosteroids are promising agents for alleviating the negative effects of salinity on plants, but the mechanism of their protective action is far from being understood. We investigated the effect of pretreatment with 24-epibrassinolide (24-EBL) on the photosynthetic and physiological parameters of potato plants under progressive salinity stress caused by root application of 100 mM NaCl. Salinity clearly inhibited primary photosynthetic processes in potato plants by reducing the contents of photosynthetic pigments, photosynthetic electron transport and photosystem II (PSII) maximal and effective quantum yields. These negative effects of salinity on primary photosynthetic processes were mainly due to toxic ionic effects on the plant's ability to oxidize the plastoquinone pool. Pretreatment with 24-EBL alleviated this stress effect and allowed the maintenance of plastoquinone pool oxidation and the efficiency of photosystem II photochemistry to be at the same levels as those in unstressed plants; however, the pretreatment did not affect the photosynthetic pigment content. 24-EBL pretreatment clearly alleviated the decrease in leaf osmotic potential under salinity stress. The stress-induced increases in lipid peroxidation and proline contents were not changed under brassinosteroid pretreatment. However, 24-EBL pretreatment increased the peroxidase activity and improved the K⁺/Na⁺ ratio in potato leaves, which were likely responsible for the protective 24-EBL action under salt stress.

24-epibrassinolide induces protection against waterlogging and alleviates impacts on the root structures, photosynthetic machinery and biomass in soybean

Plants exhibit several restrictions under waterlogging conditions, including stomatal limitations, negative impacts on gas exchange, lower nutrient uptake and reduced growth. 24-epibrassinolide (EBR) is a polyhydroxylated steroid, with the advantages to be a natural and biodegradable molecule, presenting beneficial roles in metabolic and physiological processes. The aim of this research is to investigate whether EBR can protect soybean plants against damage caused by waterlogging and evaluate the responses associated with the root and leaf anatomy, photosynthetic machinery and biomass. This study used a completely randomized factorial design with two water conditions (control and waterlogging) and three concentrations of 24-epibrassinolide (0, 5 and 10 nM EBR). This steroid stimulated the activities of enzymes linked to the antioxidant system and resulted in minor damage to the chloroplast membranes. EBR maximized the efficiency of photosystem II and improved the gas exchange, which was explained by the higher density and index of the stomata in addition to the increased chlorophyll content and electron transport rate. In root structures, EBR mitigated the impact of waterlogging on vascular cylinder and metaxilem, suggesting maintenance and functions of these structures in plants stressed.

Putrescine metabolism modulates the biphasic effects of brassinosteroids on canola and Arabidopsis salt tolerance

Brassinosteroids (BRs) are known to improve salt tolerance of plants, but not in all situations. Here, we show that a certain concentration of 24-epibrassinolide (EBL), an active BR, can promote the tolerance of canola under high-salt stress, but the same concentration is disadvantageous under low-salt stress. We define this phenomenon as hormonal stress-level-dependent biphasic (SLDB) effects. The SLDB effects of EBL on salt tolerance in canola are closely related to H₂ O₂ accumulation, which is regulated by polyamine metabolism, especially putrescine (Put) oxidation. The inhibition of EBL on canola under low-salt stress can be ameliorated by repressing Put biosynthesis or diamine oxidase activity to reduce H₂ O₂ production. Genetic and phenotypic results of bri1-9, bak1, bes1-D, and bzr1-1D mutants and overexpression lines of BRI1 and BAK1 in Arabidopsis indicate that a proper enhancement of BR signaling benefits plants in countering salt stress, whereas excessive enhancement is just as harmful as a deficiency. These results highlight the involvement of crosstalk between BR signaling and Put metabolism in H₂ O₂ accumulation, which underlies the dual role of BR in plant salt tolerance.

Nitrate reductase rather than nitric oxide synthase activity is involved in 24-epibrassinolide-induced nitric oxide synthesis to improve tolerance to iron deficiency in strawberry (Fragaria × annassa) by up-regulating the ascorbate-glutathione cycle

Involvement of nitrate reductase (NR) and nitric oxide synthase (NOS)-like enzyme in 24-epibrassinolide (EB)-triggered nitric oxide (NO) synthesis to improve iron deficiency (ID) tolerance in strawberry plants was studied. EB was sprayed to strawberry plants every two days for two weeks. Then, the EB-treated plants were pre-treated with inhibitors of NR, tungstate, or NOS, L-NAME for 3 h. During the first three weeks, Fe was supplied as 100 μM EDTA-Fe or FeSO₄ to Fe-sufficient or Fe-deficient plants, respectively. Thereafter, plants were subjected for further three weeks to control (100 μM EDTA-Fe) and Fe deficiency (ID; without Fe). ID reduced biomass, chlorophyll, and chlorophyll fluorescence, while increased oxidative stress parameters, ascorbate (AsA), glutathione (GSH), endogenous NO, and the activities of NR, NOS, and antioxidant enzymes. Pre-treatments with EB and EB + SNP improved ID tolerance of strawberry by improving leaf Fe²⁺, plant growth, and antioxidant enzyme activities, and causing a further elevation in AsA, GSH, NO, NR and NOS. L-NAME application reversed NOS activity, but it did not eliminate NO, however, tungstate application reversed both NR activity and NO synthesis in plants exposed to ID + EB, suggesting that NR is the main contributor of EB-induced NO synthesis to improve ID tolerance in strawberry plants.

Exogenous brassinosteroids increase lead stress tolerance in seed germination and seedling growth of Brassica juncea L

Lead (Pb) is a highly toxic heavy metal to plants, animals, and human beings. The use of growth regulators has reversed the effects of heavy metal stress on germination and early plant development. The aim of this study was to evaluate the effect of brassinosteroids on seed germination and seedling growth of Brassica juncea (L.) Czern. & Coss. under Pb stress conditions. Two forms of application of 24-epibrassinolide (EBL) were evaluated, application on seeds in pre-soaking and on germination paper, using EBL concentrations of 0, 10^-10, 10^-8, and 10^-6 M. Germination and seedling growth parameters were evaluated during the germination test. The activity of the enzymes superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase were determined, as well as the lead content in the seeds and seedlings. The EBL applied at the 10^-8 M concentration was the most effective in overcoming Pb stress in both forms of application. The antioxidant enzyme defense system was compromised by Pb exposure. However, 10^-8 M EBL increased the activity of antioxidant enzymes such as catalase and peroxidase to overcome the toxic effects caused by Pb. In addition, EBL at the concentration of 10^-8 M increased Pb content in seedlings without affecting seedling growth.

Nitric oxide is involved in the brassinolide-induced adventitious root development in cucumber

BACKGROUND

Brassinolide (BR), as a new type of plant hormones, is involved in the processes of plant growth and stress response. Previous studies have reported the roles of BR in regulating plant developmental processes and also response tolerance to abiotic stresses in plants. The main purpose of our study was to explore whether nitric oxide (NO) plays a role in the process of BR-induced adventitious root formation in cucumber (Cucumis sativus L.).

RESULTS

Exogenous application of 1 μM BR significantly promoted adventitious rooting, while high concentrations of BR (2-8 μM) effectively inhibited adventitious rooting. NO donor (S-nitroso-N-acerylpenicillamine, SNAP) promoted the occurrence of adventitious roots. Simultaneously, BR and SNAP applied together significantly promoted adventitious rooting and the combined effect was superior to the application of BR or SNAP alone. Moreover, NO scavenger (c-PTIO) and inhibitors (L-NAME and Tungstate) inhibited the positive effects of BR on adventitious rooting. BR at 1 μM also increased endogenous NO content, NO synthase (NOS-like) and Nitrate reductase (NR) activities, while BRz (a specific BR biosynthesis inhibitor) decreased these effects. In addition, the relative expression level of NR was up-regulated by BR and SNAP, whereas BRz down-regulated it. The application of NO inhibitor (Tungstate) in BR also inhibited the up-regulation of NR.

CONCLUSION

BR promoted the formation of adventitious roots by inducing the production of endogenous NO in cucumber.

Anabolic/anticatabolic and adaptogenic effects of 24-epibrassinolide on Lupinus angustifolius: Causes and consequences

Lupinus angustifolius L. is a legume culture known as a source of valuable feed protein and the N₂-fixator for improving soil fertility. However, its low ecological resistance does not allow for a stable yield of the crop. Earlier, we have shown that steroid phytohormone 24-epibrassinolide (EBR) increases the tolerance of lupine to chlorine ions by activating the protective proteins in ripening seeds (such as proteinase inhibitors that prevent protein breakdown) and lectins. Here we investigated the effect of EBR on the functional status of the N₂-fixing system in root nodules, protein synthesis in ripening seeds and the resistance of lupine plants to various pathogens. It was found that EBR enhanced the nodulation process, N₂-fixing activity of nitrogenase and the accumulation of poly-β-hydroxybutirate in the bacteroides, increased the leghemoglobin content in the nodules as well as the metabolic activity of bacteroides. According to data on the inclusion of ¹⁴C-leucine in maturing seed proteins, EBR increased the accumulation of protein in them against the background of a short-term decrease in protein synthesis and its subsequent regeneration to the control level. Gradual inhibition of protein synthesis, characteristic of other legumes, was observed in control variants of lupine. EBR increased lupine resistance to phytopathogenic fungi of Colletotrichum genus and insects of Noctuidae and Scarabaeidae families. We concluded that a more complete implementation of the potential productivity and sustainability of lupine under the action of EBR was achieved due to the anabolic/anti-catabolic effect on the N₂ fixation system in root nodules, as well as on protein synthesis in ripening seeds.

Effect of 24-epibrassinolide on reactive oxygen species and antioxidative defense systems in tall fescue plants under lead stress

Lead is one of the most hazardous pollutants to both the environment as well as human beings. As one of the approaches to enhance phytoremediation, brassinosteroids are predicted as a potential candidate phytohormone for assisted phytoremediation. Few studies have focused on the physiological regulations of tall fescue plants (Festuca arundinacea Schreb.), a potential phytoremediation species, for its responses to applications of brassinosteroids under lead stress. Therefore, the objectives of this study were to investigate the effects of foliar application of 24-epibrassinolide, a brassinosteroids analogue, on reactive oxygen species accumulation and antioxidative defense systems of tall fescue when exposed to lead, and ultimately its potential to be used in phytoremediation. When exposed to lead (1000 mg/kg) for 80 d, decreases in shoot and root biomass of tall fescue biomass as well as chlorophyll and carotenoid productions were found. Foliar application of 24-epibrassinolide at three rates and five applications every 7 d improved the biomass of both shoots and roots, and increased the photosynthetic pigments. The improved lead tolerance in tall fescue plants after 24-epibrassinolide applications was associated with reduced H₂O₂ and O₂^.- accumulations and increased antioxidative enzyme activities including superoxide dismutase, catalase, and guaiacol peroxidase. Additionally, osmoprotectants increased and lipid peroxidation decreased. Ultimately, foliar applications of 24-epibrassinolide enhanced the lead recovery rate of tall fescue plants, proving its potential role in phytoremediation for soil contaminated with heavy metals such as lead.

Brassinosteroid signaling delimits root gravitropism via sorting of the Arabidopsis PIN2 auxin transporter

Arabidopsis PIN2 protein directs transport of the phytohormone auxin from the root tip into the root elongation zone. Variation in hormone transport, which depends on a delicate interplay between PIN2 sorting to and from polar plasma membrane domains, determines root growth. By employing a constitutively degraded version of PIN2, we identify brassinolides as antagonists of PIN2 endocytosis. This response does not require de novo protein synthesis, but involves early events in canonical brassinolide signaling. Brassinolide-controlled adjustments in PIN2 sorting and intracellular distribution governs formation of a lateral PIN2 gradient in gravistimulated roots, coinciding with adjustments in auxin signaling and directional root growth. Strikingly, simulations indicate that PIN2 gradient formation is no prerequisite for root bending but rather dampens asymmetric auxin flow and signaling. Crosstalk between brassinolide signaling and endocytic PIN2 sorting, thus, appears essential for determining the rate of gravity-induced root curvature via attenuation of differential cell elongation.

GSK3-like kinase BIN2 phosphorylates RD26 to potentiate drought signaling in Arabidopsis

Plant steroid hormones brassinosteroids (BRs) regulate plant growth and development at many different levels. Recent research has revealed that stress-responsive NAC (petunia NAM and Arabidopsis ATAF1, ATAF2, and CUC2) transcription factor RD26 is regulated by BR signaling and antagonizes BES1 in the interaction between growth and drought stress signaling. However, the upstream signaling transduction components that activate RD26 during drought are still unknown. Here, we demonstrate that the function of RD26 is modulated by GSK3-like kinase BIN2 and protein phosphatase 2C ABI1. We show that ABI1, a negative regulator in abscisic acid (ABA) signaling, dephosphorylates and destabilizes BIN2 to inhibit BIN2 kinase activity. RD26 protein is stabilized by ABA and dehydration in a BIN2-dependent manner. BIN2 directly interacts and phosphorylates RD26 in vitro and in vivo. BIN2 phosphorylation of RD26 is required for RD26 transcriptional activation on drought-responsive genes. RD26 overexpression suppressed the brassinazole (BRZ)  insensitivity of BIN2 triple mutant bin2 bil1 bil2, and BIN2 function is required for the drought tolerance of RD26 overexpression plants. Taken together, our data suggest a drought signaling mechanism in which drought stress relieves ABI1 inhibition of BIN2, allowing BIN2 activation. Sequentially, BIN2 phosphorylates and stabilizes RD26 to promote drought stress response.

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.

OsBZR1 turnover mediated by OsSK22-regulated U-box E3 ligase OsPUB24 in rice BR response

Oryza sativa BRASSINAZOLE RESISTANT 1 (OsBZR1) is the closest rice homolog of the Arabidopsis BZR1 and bri1-EMS-SUPPRESSOR 1 (BES1)/BZR2 transcription factors. OsBZR1 plays a central role in the rice brassinosteroid signaling pathway. Despite its functional importance, the control mechanism by which the cellular stability of OsBZR1 is regulated has not yet been fully elucidated. Here, we report that a rice U-box E3 ubiquitin (Ub) ligase OsPUB24 acts as a negative regulator in the BR signaling pathway via the 26S proteasome-dependent degradation of OsBZR1. The ospub24 T-DNA knock-out mutant and Ubi:RNAi-OsPUB24 knock-down rice plants displayed enhanced seedling growth, increased lamina joint bending, and hypersensitivity to brassinolide (BL). The expressions of the BR biosynthetic genes suppressed by BR in a negative feedback loop were lower in the mutant progeny than in the wild-type rice plants, which indicated increased BR responses in the mutant line. OsPUB24 ubiquitinated OsBZR1, resulting in the proteasomal degradation of OsBZR1. In addition, the stability of OsPUB24 was downregulated by BL and bikinin, an inhibitor of Oryza sativa Shaggy/GSK3-like kinase 22 (OsSK22). OsSK22, the homolog of Arabidopsis BRASSINOSTEROID INSENSITIVE 2 (BIN2) protein kinase, phosphorylated OsPUB24 and elevated the cellular stability of OsPUB24. Our findings suggest that OsPUB24 participates in OsBZR1 turnover, and that the regulatory networks of OsPUB24, OsSK22 and OsBZR1 are crucial for fine-tuning the BR response in rice.

24-Epibrassinolide promotes arsenic tolerance in Arabidopsis thaliana L. by altering stress responses at biochemical and molecular level

In this study, the effect of 24-Epibrassinolide (EBL) on antioxidant system in Arabidopsis thaliana were investigated under arsenate [As(V)] stress. The enzyme activity of superoxide dismutase (SOD) and catalase (CAT), total antioxidant status, malondialdehyde (MDA) level and free proline content, as well as the expression levels of SOD isoforms (Cu-ZnSODs, FeSODs and MnSOD), CAT isoforms (CAT1, CAT2 and CAT3), some heat shock proteins (Hsp70-4 and Hsp90-1) and proline biosynthesis (P5CS1 and P5CS2) genes were determined in rosette leaves of eight-week old plants under exposure of 100 and 200 μM As(V) and/or 1 μM EBL treatments for 24 h. Total SOD and CAT enzyme activities increased as a result of 100 μM As(V) + EBL treatments compared to 100 μM As(V) treatment. Total antioxidant and proline levels increased in plants subjected to As(V), and the treatment of EBL together with stress caused further increase. As the MDA level increased in As-treated plants, 100 μM As(V) + EBL treatment decreased MDA level. Transcript levels of CSD1, CSD2, FSD1, FSD2, MSD1 and CAT2 genes increased as a result of combined treatment of EBL and As(V) compared to control and alone stress treatments (except CSD1 gene). Expression level of CSD3, CAT1 and CAT3 genes were downregulated in response to As(V) and/or EBL treatments. EBL application alone and in combination with As(V) elevated the expression level of P5CS1 gene dramatically. Treatment with 100 μM As(V) and EBL increased the transcript level of Hsp70-4 and Hsp90-1 genes in leaves compared to 100 μM As(V) treatment. To our best knowledge, this is the first detailed study to evaluate the improving effect of EBL on antioxidant defense system at biochemical and transcriptional level in A. thaliana plants under As(V) stress.

Effects of exogenous 24-epibrassinolide and brassinazole on negative gravitropism and tension wood formation in hybrid poplar (Populus deltoids × Populus nigra)

Exogenous 24-epibrassinolide (BL) and brassinazole (BRZ) have regulatory roles in G-fiber cell wall development and secondary xylem cell wall carbohydrate biosynthesis during tension wood formation in hybrid poplar. Brassinosteroids (BRs) play important roles in regulating gravitropism and vasculature development. Here, we report the effect of brassinosteroids on negative gravitropism and G-fiber cell wall development of the stem in woody angiosperms. We applied exogenous 24-epibrassinolide (BL) or its biosynthesis inhibitor brassinazole (BRZ) to slanted hybrid poplar trees (Populus deltoids × Populus nigra) and measured the morphology of gravitropic stems, anatomy and chemistry of secondary cell wall. We furthermore analyzed the expression levels of auxin transport and cellulose biosynthetic genes after 24-epibrassinolide (BL) or brassinazole (BRZ) application. The BL-treated seedlings showed no negative gravitropism bending, whereas application of BRZ dramatically enhanced negative gravitropic bending. BL treatment stimulated secondary xylem fiber elongation and G-fiber formation on the upper side of stems but delayed G-fiber maturation. BRZ inhibited xylem fiber elongation but induced the production of more mature G-fibers on the upper side of stems. Wood chemistry analyses and immunolocalization demonstrated that BL and BRZ treatments increased the cellulose content and modified the deposition of cell wall carbohydrates including arabinose, galactose and rhamnose in the secondary xylem. The expression of cellulose biosynthetic genes, especially those related to cellulose microfibril deposition (PtFLA12 and PtCOBL4) was significantly upregulated in BL- and BRZ-treated TW stems compared with control stems. The significant differences of G-fibers development and negative gravitropism bending between 24-epibrassinolide (BL) and brassinazole (BRZ) application suggest that brassinosteroids are important for secondary xylem development during tension wood formation. Our findings provide potential insights into the mechanism by which BRs regulate G-fiber cell wall development to accomplish negative gravitropism in TW formation.

Exogenous 24-epibrassinolide enhanced benzene detoxification in Chlorophytum comosum via overexpression and conjugation by glutathione

Benzene, a hydrophobic xenobiotic, induces cell damage in both humans and plants. Due to its volatilization, benzene is an airborne environmental problem. The potential of an exogenous bioactive brassinosteroid phytohormone to enhance benzene removal for phytoremediation was investigated. Chlorophytum comosum had higher brassinosteroids content under benzene stress. Plant treated with 24-epibrassinolide (EBR) removed significantly more gaseous benzene than untreated plants under both light and dark conditions at an initial benzene of 12.75 μmol in the systematic chambers (P < 0.05). Although benzene increased malondialdehyde in plant tissue, EBR-treated plants lowered this lipid peroxidation by enhancing their antioxidant content and increasing benzene detoxification-related genes expression, including ascorbic acid (AsA), homogentisate phytyltransferase (HPT), and glutathione synthethase (GS). This contributed to maintaining higher photosynthetic performances. Moreover, EBR-treated plants had higher gene expression of ferredoxin-NADP reductase (FNR) and glucose-6-phosphate 1-dehydrogenase (G6PDH), thus promoting NADPH biosynthesis to cope with benzene under light and dark conditions, respectively. Further, higher glutathione biosynthesis promoted more glutathione conjugate of benzene products including S-phenylcysteine (SPC) in EBR-treated plants. Hence, application of exogenous EBR as foliar spray provided for enhanced benzene detoxification via antioxidant content, benzene detoxification-related genes and benzene conjugation products with glutathione (GSH) and consequently greater gaseous benzene removal.

The role of chloroplasts in the oxidative stress that is induced by zearalenone in wheat plants - The functions of 24-epibrassinolide and selenium in the protective mechanisms

This study focused on the idea that the toxic effect of zearalenone (ZEA) and the protective actions of the brassinosteroid - 24-epibrassinolide (EBR) as well as selenium are dependent on its accumulation in chloroplasts to a high degree. These organelles were isolated from the leaves of oxidative stress-sensitive and stress-tolerant wheat cultivars that had been grown from grains that had been incubated in a solution of ZEA (30 μM), Na₂SeO₄ (Se, 10 μM), EBR (0.1 μM) or in a mixture of ZEA with Se or EBR. Ultra-high performance liquid chromatography techniques indicated that ZEA was adsorbed in higher amounts in the chloroplasts in the sensitive rather than tolerant cultivar. Although the brassinosteroids and Se were also accumulated in the chloroplasts, higher levels were only found in the tolerant cultivar. The application of EBR increased the homocastasterone content, especially in the chloroplasts of the tolerant plant and after the addition of ZEA. The presence of both protectants caused a decrease in the ZEA content in studied organelles and resulted in diminishing of the oxidative stress (i.e. changes in the activity of the antioxidative enzymes). Moreover, a recovery of photosystem II and decrease in the negative impact of ZEN on Hsp90 transcript accumulation was observed in plants.

Responses of the weed Bidens pilosa L. to exogenous application of the steroidal saponin protodioscin and plant growth regulators 24-epibrassinolide, indol-3-acetic acid and abscisic acid

The exogenous application of plant hormones and their analogues has been exploited to improve crop performance in the field. Protodioscin is a saponin whose steroidal moiety has some similarities to plant steroidal hormones, brassinosteroids. To test the possibility that protodioscin acts as an agonist or antagonist of brassinosteroids or other plant growth regulators, we compared responses of the weed species Bidens pilosa L. to treatment with protodioscin, brassinosteroids, auxins (IAA) and abscisic acid (ABA). Seeds were germinated and grown in agar containing protodioscin, dioscin, brassinolides, IAA and ABA. Root apex respiratory activity was measured with an oxygen electrode. Malondialdehyde (MDA) and antioxidant enzymes activities were assessed. Protodioscin at 48-240 μm inhibited growth of B. pilosa seedlings. The steroidal hormone 24-epibrassinolide (0.1-5 μm) also inhibited growth of primary roots, but brassicasterol was inactive. IAA at higher concentrations (0.5-10.0 μm) strongly inhibited primary root length and fresh weight of stems. ABA inhibited all parameters of seedling growth and also seed germination. Respiratory activity of primary roots (KCN-sensitive and KCN-insensitive) was activated by protodioscin. IAA and ABA reduced KCN-insensitive respiration. The content of MDA in primary roots increased only after protodioscin treatment. All assayed compounds increased APx and POD activity, with 24-epibrassinolide being most active. The activity of CAT was stimulated by protodioscin and 24-epibrassinolide. The results revealed that protodioscin was toxic to B. pilosa through a mechanism not related to plant growth regulator signalling. Protodioscin caused a disturbance in mitochondrial respiratory activity, which could be related to overproduction of ROS and consequent cell membrane damage.

24-Epibrassinolide application in plants: An implication for improving drought stress tolerance in plants

Drought stress is one of most dramatic abiotic stresses, reduces crop yield significantly. Application of hormones proved as an effective drought stress ameliorating approach. 24-Epibrassinolide (EBL), an active by-product from brassinolide biosynthesis increases drought stress tolerance in plants significantly. EBL application enhances plant growth and development under drought stress by acting as signalling compound in different physiological processes. This article discussed potential role of 24-epibrassinolide application and drought tolerance in plants. Briefly, EBL sustains or improves plant growth and yield by enhancing carbon assimilation rate, maintaining a balance between ROS and antioxidants and also plays important role in solute accumulation and water relations. Furthermore, we also compared different EBL application methods and concluded that seed priming and foliar application are more productive as compared with root application method. In conclusion, EBL is very impressive phyto-hormone, which can ameliorate drought stress induced detrimental effects in plants.

24-Epibrassinolide-alleviated drought stress damage influences antioxidant enzymes and autophagy changes in peach (Prunus persicae L.) leaves

Drought stress is a serious threat to agriculture and the environment. Brassinosteroids (BRs) increase tolerance to drought stress of plant. Autophagy plays important roles in plant responses to drought stress; however, there are few reports on autophagy in peach (Prunus persica). In total, 23 putative autophagy-related genes (ATGs) in peach were identified using ATGs from the Arabidopsis thaliana genome as query in BLASTx algorithm-based searches. Under drought stress, the photosynthetic abilities of peach leaves decreased, while antioxidant enzyme activities, autophagy and ATG expression increased. A correlation analysis showed that antioxidant enzyme activities are inversely correlated to the expression levels of the PpATGs. During drought, the PpATG8s and some PpATG18s had the strongest responses. To investigate enhanced drought-stress tolerance, peach was treated with water, 100 nM 24-epibrassinolide (EBR), 1 μM EBR, 10 μM EBR and 1 μM voriconazole. Exogenous EBR at 1 μM decreased the malondialdehyde (MDA) content under drought stress when compared with water-, 1 μM voriconazole-, 100 nM EBR- and 10 μM EBR-treated peach leaf. The 1-μM EBR application increased superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), ascorbate peroxidase (APX) and glutathione peroxidase (GR) activities during drought stress. In addition, the expression levels of PpATGs were inhibited by EBR. Thus, the 1-μM EBR treatment alleviated drought-stress damage to peach leaves, decreased PpATG expression levels and reduced the number of autophagosomes.

Occurrence of brassinosteroids and influence of 24-epibrassinolide with brassinazole on their content in the leaves and roots of Hordeum vulgare L. cv. Golden Promise

24-epibrassinolide overcame the inhibitory effect of brassinazole on the barley growth and the content of brassinosteroids. The present work demonstrates the occurrence of mainly castasterone, brassinolide and cathasterone and lower amounts of 24-epibrassinolide, 24-epicastasterone, 28-homobrassinolide, typhasterol, 6-deoxocastasterone and 6-deoxotyphasterol in 14-day-old de-etiolated barley (Hordeum vulgare L. cv. Golden Promise). We also investigated the endogenous level of brassinosteroids (BRs) in barley seedlings treated with 24-epibrassinolide (EBL) and/or brassinazole (Brz). To our knowledge, this is the first report related to the occurrence of BRs and application of EBL and Brz in terms of the endogenous content of BRs in barley. Brz as a specific inhibitor of BR biosynthetic reactions decreased the level of BRs in the leaves. Application of EBL showed a weak promotive effect on the BR content in Brz-treated seedlings. Brz also inhibited growth of the seedlings; however, addition of EBL overcame the inhibition. The EBL applied alone at 0.01-1 µM increased the BR level in the leaves but at 10 µM lowered the BR content. In opposition to leaves, the Brz in the concentration range from 0.1 to 1 µM did not significantly affect the content of BRs in the roots. However, application of 10 µM Brz caused BRs to decrease, but treatment of EBL concentrations overcame the inhibitory effect of Brz.

Evaluation of the protective role of exogenous growth regulators against Ni toxicity in woody shrub Daphne jasminea

The results provide a significant verification of the activity of exogenously applied phytohormones: gibberellic acid, jasmonic acid, and brassinolide in the modulation of the plant's response to nickel treatment. The study investigated nickel accumulation and its toxicity to Daphne jasminea shoots cultured in vitro with or without exogenous supplementation with phytohormones: gibberellic acid (GA3), jasmonic acid (JA), and brassinolide (BL). The aim was to verify the modulatory effect of exogenous plant growth regulators (PGRs) on plant reaction to Ni excess. The combined action of Ni and PGRs was evaluated at the anatomical, ultrastructural, and biochemical levels. Nickel toxicity was manifested in decreased biomass accretion and growth tolerance index (83-53.6%), attributed to enhanced synthesis of growth inhibitors, mainly abscisic acid. As a defence reaction, endogenous gibberellins accumulated. Exogenous GA3 ameliorated the plant reaction to Ni stress, inducing proliferation and growth rate. Ni tolerance in the presence of GA3 was attributed to peroxisomal reactions that stimulated the synthesis of endogenous JA. In contrast, the application of BL caused enhanced Ni accumulation. Plants suffered from pronounced stress due to massive oxidation. The defence strategy of plants subjected to Ni and BL involved cell wall rearrangements. Exogenous JA stimulated the synthesis of active auxins and salicylic acid, contributing to enhanced mitotic activity within explants. However, JA disturbed the integrity of chloroplasts and lamellar compartments. Our study revealed that an action of exogenous PGRs may either enhance tolerance to Ni or increase metal toxicity in D. jasminea. Particularly in in vitro culture, where explants are subjected to external phytohormonal stimuli, the combined effects of supplemental PGRs may enhance stress and substantially affect plant development. Our results provide a significant verification of exogenous PGRs activity in the modulation of plant response to nickel.

Exogenous brassinosteroids altered cell length, gibberellin content, and cellulose deposition in promoting carrot petiole elongation

Brassinosteroid (BR) is a predominant plant hormone in regulating cell elongation and cell size. BR-deficient mutants display reduced plant growth and dwarfism in Arabidopsis and rice. In carrot, BRs promote petiole elongation, but its underlying mechanism involving exogenous BR remains unknown. Here, weighted gene co-expression network analysis and promoter region analysis were adopted to identify the potential genes that interacted with DcBZR1/BES1. Bioactive gibberellin (GA) level and cellulose deposition were also determined in the control and treated plants. Quantitative real-time PCR was performed to detect the expression profiles of GA biosynthesis-related genes, GA signaling genes, and cellulose synthase genes. Bioactive GA level and cellulose deposition were upregulated after the petioles were treated with 24-epibrassinolide (24-EBL). The most putative DcBZR1/BES1 genes were clustered in yellow module. The expression level of DCAR_009411 (a GA5-like gene) was significantly induced after 3 h of treatment. The expression levels of DCAR_019754 and DCAR_013973 (CESA-like genes) were also significantly induced after 3 h of 24-EBL treatment. Our results suggested that the effect of BR on carrot petiole growth was quick. These results also provided potential insights into the mechanism by which BRs modulate GA and cellulose synthesis to promote cell elongation in carrot petioles.

Exogenous 24-Epibrassinolide alleviates oxidative damage from copper stress in grape (Vitis vinifera L.) cuttings

Copper (Cu) stress is the most common abiotic stress experienced in vineyards owing to the copper-based fungicides application. Plant hormones, including 24-Epibrassinolide (EBR), may alleviate the adverse impacts of heavy metal stress on plants. We investigated the effects of EBR pretreatment on root morphological parameters, active oxygen metabolism, osmolytes contents, antioxidant enzyme activity, endogenous phytohormone contents, and ascorbate-glutathione (AsA-GSH) cycle activity of one-year-old grape (Vitis vinifera L.) cuttings under Cu stress. Pretreatment with EBR significantly enhanced root morphological parameters (total root length, root surface area, root diameter, root volume, and tip number), increased soluble protein and proline contents, and significantly decreased the contents of H₂O₂, O₂^⋅-, and malondialdehyde (MDA) in roots and leaves. EBR pretreatment increased the activities of superoxide dismutase (SOD), catalase (CAT), peroxidase oxidase (POD), and the contents of the endogenous phytohormones abscisic acid, jasmonic acid, and salicylic acid in the leaves. In addition, EBR regulated the balance of the AsA-GSH cycle by increasing the activities of monodehydroascorbate reductase (MDHAR), glutathione peroxidase (GR), ascorbate peroxidase (APX), and dehydroascorbate reductase (DHAR), and the contents of the antioxidant ascorbate (AsA) and dehydroascorbic acid (DHA), but the contents of glutathione (GSH) and oxidized glutathione (GSSG) decreased. Among the treatments tested, pretreatment with 0.10 mg/L EBR showed the optimal performance for alleviation of Cu toxicity. The results show that exogenous brassinosteroids reduce oxidative damage and improve the tolerance of Cu stress of grapevine cuttings.

24-Epibrassinolide Ameliorates Endogenous Hormone Levels to Enhance Low-Temperature Stress Tolerance in Cucumber Seedlings

Phytohormone biosynthesis and accumulation are essential for plant growth and development and stress responses. Here, we investigated the effects of 24-epibrassinolide (EBR) on physiological and biochemical mechanisms in cucumber leaves under low-temperature stress. The cucumber seedlings were exposed to treatments as follows: NT (normal temperature, 26 °C/18 °C day/night), and three low-temperature (12 °C/8 °C day/night) treatments: CK (low-temperature stress); EBR (low-temperature and 0.1 μM EBR); and BZR (low-temperature and 4 μM BZR, a specific EBR biosynthesis inhibitor). The results indicated that low-temperature stress proportionately decreased cucumber seedling growth and the strong seedling index, chlorophyll (Chl) content, photosynthetic capacity, and antioxidant enzyme activities, while increasing reactive oxygen species (ROS) and malondialdehyde (MDA) contents, hormone levels, and EBR biosynthesis gene expression level. However, EBR treatments significantly enhanced cucumber seedling growth and the strong seedling index, chlorophyll content, photosynthetic capacity, activities of antioxidant enzymes, the cell membrane stability, and endogenous hormones, and upregulated EBR biosynthesis gene expression level, while decreasing ROS and the MDA content. Based on these results, it can be concluded that exogenous EBR regulates endogenous hormones by activating at the transcript level EBR biosynthetic genes, which increases antioxidant enzyme capacity levels and reduces the overproduction of ROS and MDA, protecting chlorophyll and photosynthetic machinery, thus improving cucumber seedling growth.

Effects of salicylic acid, Epi-brassinolide and calcium on stress alleviation and Cd accumulation in tomato plants

Salicylic acid (SA), Epi-brassinolide (EBL) and calcium (Ca) play crucial roles in plant development and mediate plant response to biotic and abiotic stress. This study was aimed to investigate the possible mediatory role of SA, EBL, Ca or their combination in protecting tomato plants from cadmium (Cd) toxicity. According to the results, Cd stress resulted in a significant reduction of plant dry mass, photosynthetic pigment content as well as photosynthetic rate. Exogenous application of SA decreased the malondialdehyde (MDA) level by 39.27% and increased catalase (CAT) activity by 81.17%. SA and EBL treatment significantly increased chlorophyll a (Chl a), chlorophyll b (Chl b) content, photosynthetic rate (Pn) as well as water use efficiency (WUE). SA+EBL (1:1)/Ca+SA+EBL (1:1:1) treatment obviously alleviated Cd-induced growth inhibition, the dry mass of different tomato organs were significantly increased (p < 0.05). Especially in Ca+SA+EBL treated plants, the dry mass of roots, stems and leaves increased by 141.18%, 128.57% and 118.52%, respectively. Besides, SA+EBL and Ca+SA+EBL treatments reduced the MDA level, but increased photosynthetic pigment concentration and photosynthetic efficiency. CAT activity was increased by 62.92% in Ca+SA+EBL treated plants, the WUE was increased by 557.76% in SA+EBL pretreated plants. Moreover, exogenous application of SA, SA+EBL and Ca+SA+EBL significantly decreased Cd accumulation in tomato organs (p < 0.05) compared with Cd-stressed plants. Taken together, our results indicated that exogenous application of SA, EBL and Ca individually or in combination could alleviate Cd toxicity in tomato plants, although the extent varies.

The transcription factor FcWRKY40 of Fortunella crassifolia functions positively in salt tolerance through modulation of ion homeostasis and proline biosynthesis by directly regulating SOS2 and P5CS1 homologs

Although some WRKYs have been characterized, regulatory roles of most WRKYs remain poorly understood. Herein, we elucidated function of FcWRKY40 from Fortunella crassifolia in salt tolerance via overexpression and virus-induced gene silencing (VIGS) and unraveled its target genes. Overexpression of FcWRKY40 enhanced salt tolerance in transgenic tobacco and lemon, while silencing of FcWRKY40 increased salt susceptibility. Homolog genes of Salt Overly Sensitive 2 (SOS2) and Δ-1-pyrroline-5-carboxylate synthetase 1 (P5CS1) were dramatically up-regulated in transgenic lemon but down-regulated in VIGS line. Consistently, transgenic lemon displayed lower Na+ and higher proline concentrations, whereas the silenced line accumulated more Na+ but less proline. Treatment of transgenic lemon with 24-epi-brassinolide compromised salt tolerance, while supply of exogenous proline partially restored salt tolerance of the VIGS line. FcWRKY40 specifically binds to and activates promoters of FcSOS2 and FcP5CS1. FcWRKY40 was up-regulated by ABA and salt, and confirmed as a target of ABA-responsive element binding factor 2 (FcABF2). Moreover, salt treatment up-regulated FcABF2 and FcP5CS1, and elevated proline concentrations. Taken together, our findings demonstrate that FcWRKY40 participates in the ABA signaling pathway and as a positive regulator functions in salt tolerance by regulating genes involved in ion homeostasis and proline biosynthesis.

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

BRs are polyhydroxylated sterol derivatives, classified as phytohormones. Plants of Brassica juncea var. Varuna were grown in pots and an aqueous solution (10^-8 M) of two brassinosteroid isomers 28-homobrassinolide (HBL) and 24-epibrassinolide (EBL) of same concentration (10^-8 M) was applied to their leaves. The treatment up-regulated the photosynthetic machinery directly by enhancing water splitting activity, photochemical quenching, non-photochemical quenching, maximum PSII efficiency, actual PSII efficiency, electron transport rate, stomatal movement, stomatal conductance, internal CO₂ concentration, transpiration rate, net photosynthetic rate and carbohydrate synthesis. Moreover, the level of biochemical enzymes (carbonic anhydrase and nitrate reductase), reactive oxygen species (superoxide and hydrogen peroxide) generation, antioxidant enzyme activity and mineral status (C, N, Mg, P, S, K), which indirectly influence the rate of photosynthesis, also improved in the treated plants. Out of the two BR analogues tested, EBL excelled in its effects over HBL.

Interactive effect of 24-epibrassinolide and silicon alleviates cadmium stress via the modulation of antioxidant defense and glyoxalase systems and macronutrient content in Pisum sativum L. seedlings

BACKGROUND

This study assessed the effects of 24-epibrassinolide (EBL, 10-7M) and silicon (2 mM) on the alleviation of cadmium (Cd, 150 mg L-1) toxicity in Pisum sativum L. seedlings via the modulation of growth, antioxidant defense, glyoxalase system, and nutrient uptake.

RESULTS

Shoot and root lengths declined by 46.43% and 52.78%, respectively, following Cd stress. Shoot and root dry weights also declined with Cd toxicity. Biochemical and physiological aspects exhibit significant decline including total chlorophyll (33.09%), carotenoid (51.51%), photosynthetic efficiency (32.60%), photochemical quenching (19.04%), leaf relative water content (40.18%), and gas exchange parameters (80.65%). However, EBL or Si supplementation alone or in combination modulates the previously mentioned parameters. Cadmium stress increased proline and glycine betaine (GB) contents by 4.37 and 2.41-fold, respectively. Exposure of plants to Cd stress increased the accumulation of H2O2, malondialdehyde content, electrolyte leakage, and methylglyoxal, which declined significantly with EBL and Si supplementation, both individually and in combination. Similarly, Cd stress adversely affected enzymatic and non-enzymatic antioxidants, but EBL and/or Si supplementation maintained antioxidant levels. Glyoxalase I (GlyI) accumulated after Cd stress and increased further with the application of EBL and Si. However, GlyII content declined after Cd stress but increased with supplementation of EBL and Si. Cadmium accumulation occurred in the following order: roots > shoots>leaves. Supplementation with EBL and Si, individually and in combination reduced Cd accumulation and enhanced the uptake of macronutrients and micronutrients in shoots and roots, which declined with Cd toxicity.

CONCLUSION

The application of 24-EBL and Si, individually and in combination, alleviated the adverse effects of Cd by improving growth, biochemical parameters, nutrient uptake, osmolyte accumulation, and the anti-oxidative defense and glyoxalase systems in Pisum sativum seedlings.

Interaction of 24-epibrassinolide and salicylic acid regulates pigment contents, antioxidative defense responses, and gene expression in Brassica juncea L. seedlings under Pb stress

Lead (Pb) is considered one the most hazardous pollutant, and its accumulation in soil and plants is of prime concern. To understand the role of plant hormones in combating heavy metal stress, the present study was planned to assess the interactive effects of 24-epibrassinolide (EBL) (10^-7 M) and salicylic acid (SA) (1 mM) in regulating growth, pigment contents, antioxidative defense response, and gene expression in Brassica juncea L. seedlings exposed to different concentrations of Pb metal (0.25, 0.50, and 0.75 mM). Reduction in root and shoot lengths, chlorophyll and carotenoid content, and non-enzymatic antioxidants like glutathione, ascorbic acid, and tocopherol in response to Pb toxicity was observed. The enzymatic antioxidants such as guaiacol peroxidase (POD), ascorbate peroxidase (APOX), glutathione peroxidase (GR), dehydroascorbate reductase (DHAR), monodehydroascorbate redductase (MDHAR), glutathione-S-transferease (GST), and glutathione peroxidase (GPOX) were lowered in response to Pb treatments. Other antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), and polyphenol oxidase (PPO) enhanced under metal stress. Co-application of EBL + SA to 0.75 mM Pb-treated seedlings resulted in improvement of root and shoot lengths, chlorophyll, and carotenoid contents. Similarly, glutathione, ascorbic acid, and tocopherol contents were also elevated. Enzymatic antioxidants were also significantly enhanced in response to pre-sowing combined treatment of both hormones. Gene expression analysis suggested elevation in expression of CAT, POD, GR, DHAR, and GST genes by application of EBL. Our results reveal that Pb metal toxicity caused adverse impact on B. juncea L. seedlings, but pre-soaking treatment with EBL and SA individually and in combination help seedlings to counter the ill effects of Pb by improving growth, contents of pigment, and modulation of antioxidative defense system. The combined application of EBL and SA was found to be more effective in ameliorating Pb stress as compared to their individual treatments.

24-Epibrassinolide-induced alterations in the root cell walls of Cucumis sativus L. under Ca(NO3)2 stress

Brassinosteroids (BRs) can effectively alleviate the oxidative stress caused by Ca(NO₃)₂ in cucumber seedlings. The root system is an essential organ in plants due to its roles in physical anchorage, water and nutrient uptake, and metabolite synthesis and storage. In this study, 24-epibrassinolide (EBL) was applied to the cucumber seedling roots under Ca(NO₃)₂ stress, and the resulting chemical and anatomical changes were characterized to investigate the roles of BRs in alleviating salinity stress. Ca(NO₃)₂ alone significantly induced changes in the components of cell wall, anatomical structure, and expression profiles of several lignin biosynthetic genes. Salt stress damaged several metabolic pathways, leading to cell wall reassemble. However, EBL promoted cell expansion and maintained optimum length of root system, alleviating the oxidative stress caused by Ca(NO₃)₂. The continuous transduction of EBL signal thickened the secondary cell wall of casparian band cells, thus resisting against ion toxicity and maintaining water transport.

The effect of 24-epibrassinolide on the green alga Acutodesmus obliquus (Chlorophyceae)

Brassinosteroids play an important role in the plant growth and development as well as in the adaptation of plants to environmental stresses. Studies have shown the effect of 24-epibrassinolide (EBL) in the range of concentrations 0.0001-10 μM on the green unicellular alga Acutodesmus obliquus (Chlorophyceae) during 7 days of cultivation. EBL is an effective stimulator of algal growth as it causes an increase in the number of cells and the contents of selected metabolites such as proteins, monosaccharides, and photosynthetic pigments (chlorophylls, carotenes, and xanthophylls). Furthermore, EBL inhibits the formation of reactive oxygen species such as hydrogen peroxide and oxidative damage as evidenced by a decrease of the lipid peroxidation. The positive effect of EBL resulting from the cellular oxidative state can be alleviated by antioxidants such as ascorbate peroxidase, catalase, superoxide dismutase, and ascorbate.

[Effects of exogenous 2,4-epibrassinolide on the growth and redox balance of cucumber seedlings under NaHCO3 stress]

The effects of 0.2 μmol·L^-1 exogenous 2,4-epibrassinolide (EBR) on the growth and reactive oxygen species metabolism of cucumber seedlings ('Jinyan 4' cucumber) under salt-alkaline stress (30 mmol·L^-1 NaHCO₃) were examined by hydroponics method. The results showed that NaHCO₃ stress significantly induced production of O₂^-· and accumulation of H₂O₂ in leaves and roots, resulting in the increases of MDA content and electrolyte leakage. Under NaHCO₃ stress, activities of superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, dehydroascorbatereductase, monodehydrodroascorbate reductase, and glutathione reductase as well as contents of ascorbic acid and glutathione were firstly increased and then decreased with progress of stress time. Exogenous EBR application significantly increased the activities of antioxidant enzymes and contents of antioxidants as well as the ratio of AsA/DHA (dehydroascorbic acid) and GSH/GSSG (L-glutathione oxidized) in leaves and roots of cucumber under NaHCO₃ stress. Such changes improved the redox hemostasis in plants, reduced the level of reactive oxygen species, and alleviated the membrane lipid peroxidation. Together, they increased the alkaline tolerance of cucumber seedlings.

Modulation of antioxidative defense expression and osmolyte content by co-application of 24-epibrassinolide and salicylic acid in Pb exposed Indian mustard plants

The study focuses on potential of combined pre-soaking treatment of 24-Epibrassinolide (EBL) and Salicylic acid (SA) in alleviating Pb phytotoxicity in Brassica juncea L. plants. The seeds after treatment with combination of both the hormones were sown in mixture of soil, sand and manure (3:1:1) and were exposed to Pb concentrations (0.25mM, 0.50mM and 0.75mM). After 30 days of growth, the plants were harvested and processed, for quantification of various metabolites. It was found that pre-sowing of seeds in combination of EBL and SA, mitigated the adverse effects of metal stress by modulating antioxidative defense response and enhanced osmolyte contents. Dry matter content and heavy metal tolerance index were enhanced in response to co-application of EBL and SA. The levels of superoxide anions, hydrogen peroxide and malondialdehyde were lowered by the combined treatment of hormones. Enhancement in activities of guaiacol peroxidase, catalase, glutathione reductase and glutathione-s-transferase were recorded. Contents of glutathione, tocopherol and ascorbic acid were also enhanced in response to co-application of both hormones. Expression of POD, CAT, GR and GST1 genes were up-regulated whereas SOD gene was observed to be down-regulated. Contents of proline, trehalose and glycine betaine were also reported to be elevated as a result of treatment with EBL+SA. The results suggest that co-application of EBL+SA may play an imperative role in improving the antioxidative defense expression of B. juncea plants to combat the oxidative stress generated by Pb toxicity.

Role of 24-epibrassinolide (EBL) in mediating heavy metal and pesticide induced oxidative stress in plants: A review

Industrialization and urbanization have posed serious threats to the environment. Excessive release of heavy metals from industrial effluents and overuse of pesticides in modern agriculture are limiting crop production by polluting environment and deteriorating food quality. Sustaining food quality under heavy metals and pesticide stress is crucial to meet the increasing demands for food. 24-Epibrassinolide (EBL), a ubiquitously occurring plant growth hormone shows great potential to alleviate heavy metals and pesticide stress in plants. This review sums up the potential role of EBL in ameliorating heavy metals and pesticide toxicity in plants extensively. EBL application increases plant's overall growth, biomass accumulation and photosynthetic efficiency by the modulation of numerous biochemical and physiological processes under heavy metals and pesticide stress. In addition, EBL scavenges reactive oxygen species (ROS) by triggering the production of antioxidant enzymes such as SOD, CAT, POX etc. EBL also induces the production of proline and soluble proteins that helps in maintaining osmotic potential and osmo-protection under both heavy metals and pesticide stress. At the end, future needs of research about the application of 24-epibrassinolide have also been discussed.

The F-box Protein KIB1 Mediates Brassinosteroid-Induced Inactivation and Degradation of GSK3-like Kinases in Arabidopsis

The glycogen synthase kinase-3 (GSK3) family kinases are central cellular regulators highly conserved in all eukaryotes. In Arabidopsis, the GSK3-like kinase BIN2 phosphorylates a range of proteins to control broad developmental processes, and BIN2 is degraded through unknown mechanism upon receptor kinase-mediated brassinosteroid (BR) signaling. Here we identify KIB1 as an F-box E3 ubiquitin ligase that promotes the degradation of BIN2 while blocking its substrate access. Loss-of-function mutations of KIB1 and its homologs abolished BR-induced BIN2 degradation and caused severe BR-insensitive phenotypes. KIB1 directly interacted with BIN2 in a BR-dependent manner and promoted BIN2 ubiquitination in vitro. Expression of an F-box-truncated KIB1 caused BIN2 accumulation but dephosphorylation of its substrate BZR1 and activation of BR responses because KIB1 blocked BIN2 binding to BZR1. Our study demonstrates that KIB1 plays an essential role in BR signaling by inhibiting BIN2 through dual mechanisms of blocking substrate access and promoting degradation.