Influence of Exogenous 24-Epicasterone on the Hormonal Status of Soybean Plants.

Brassinosteroids (BRs) are key phytohormones involved in the regulation of major processes of cell metabolism that guide plant growth. In the past decades, new evidence has made it clear that BRs also play a key role in the orchestration of plant responses to many abiotic and biotic stresses. In the present work, we analyzed the impact of foliar treatment with 24-epicastasterone (ECS) on the endogenous content of major phytohormones (auxins, salicylic acid, jasmonic acid, and abscisic acid) and their intermediates in soybean leaves 7 days following the treatment. Changes in the endogenous content of phytohormones have been identified and quantified by LC/MS. The obtained results point to a clear role of ECS in the upregulation of auxin content (indole-3-acetic acid, IAA) and downregulation of salicylic, jasmonic, and abscisic acid levels. These data confirm that under optimal conditions, ECS in tested concentrations of 0.25 µM and 1 µM might promote growth in soybeans by inducing auxin contents. Benzoic acid (a precursor of salicylic acid (SA)), but not SA itself, has also been highly accumulated under ECS treatment, which indicates an activation of the adaptation strategies of cell metabolism to possible environmental challenges.

Brassinosteroids application induces phosphatidic acid production and modify antioxidant enzymes activity in tobacco in calcium-dependent manner.

Brassinosteroids (BRs) are steroid hormones regulating various aspects of plant metabolism, including growth, development and stress responses. However, little is known about the mechanism of their impact on antioxidant systems and phospholipid turnover. Using tobacco plants overexpressing H+/Ca2+vacuolar Arabidopsis antiporter CAX1, we showed the role of Ca2+ ion balance in the reactive oxygen species production and rapid phosphatidic acid accumulation induced by exogenous BR. Combination of our experimental results with public transcriptomic and proteomic data revealed a particular role of Ca2+-dependent phospholipid metabolizing enzymes in BR signaling. Here we provide novel insights into the role of calcium balance and lipid-derived second messengers in plant responses to exogenous BRs and propose a complex model integrating BR-mediated metabolic changes with phospholipid turnover.

Seed germination, respiratory processes and phosphatidic acid accumulation in Arabidopsis diacylglycerol kinase knockouts - The effect of brassinosteroid, brassinazole and salinity.

Using Arabidopsis thaliana wild type (WT) plants and diacylglycerol kinase knockouts (single mutants - dgk3, dgk1, dgk6; double mutants - dgk3dgk7, dgk5dgk6, dgk1dgk2) we observed that the inhibitor of brassinosteroid (BR) biosynthesis, brassinazole (BRZ), drastically decreased germination of dgk mutants under salt stress, while BRZ co-administration with 24-epibrassinolide (EBL) partially improved germination rates. We also observed a statistically significant decrease in alternative and cytochrome respiratory pathways in response to BRZ treatment under salinity conditions. We showed that production of the lipid second messenger phosphatidic acid (PA) is impaired in dgk mutants in response to EBL treatment and inhibitor of diacylglycerol kinase (DGK) - R59022. This study demonstrates that dgk mutants possess lower germination rates, lower total respiration rates, an alternative respiratory pathway and PA content under optimal and high salinity conditions in response to EBL treatment comparing to WT plants.

Effect of 24-epibrassinolide on Brassica napus alternative respiratory pathway, guard cells movements and phospholipid signaling under salt stress.

Using Brassica napus roots we observed statistically significant increase in alternative respiratory pathway in response to exogenous 24-epibrassinolide (EBL) under optimal conditions and salinity. Also we observed activation of phospholipid signaling under the same conditions in response to EBL by measuring levels of lipid second messengers - diacylglycerol (DAG) and phosphatidic acid (PA). We found that brassinosteroids cause closure of stomata in isolated leaf disks while inhibitors of alternative oxidase cancelled these effects. This study demonstrates that BRs activate total respiration rate, alternative respiratory pathway, production of PA and DAG, stimulate stomata closure and growth under optimal conditions and salinity. Also, specific inhibitor of brassinosteroids biosynthesis decreased alternative respiratory pathway and production of lipid messengers in rape plants.