24‐Epibrassinolide promotes activation of physiological compensation mechanisms in response to drought stress and rehydration and improves yield in soybean

Abstract Drought stress is the main limiting factor for the yield of soybean crop in the world. Alternatives to minimize the impacts of water deficit on plants involve the application of plant bioregulators, among which Brassinosteroids stand out. In this study, nodulated soybean plants were used to investigate the ability of the 24‐epibrassinolide (EBR) bioregulator to reduce the damage caused to physiological mechanisms, growth and yield, after application in the vegetative stage of soybean plants, subjected to drought stress and rehydration. Application of EBR in plants subjected to drought stress promoted better performance in the rates of transpiration, photosynthesis and instantaneous water use efficiency compared to plants without EBR. The lowest reductions in relative water content and leaf water potential were recorded in stressed soybean plants treated with EBR. Plants under drought stress treated with EBR showed increase in the effective photochemical efficiency of PSII. In addition, soybean plants that received EBR application showed lower oxidative damage to cell membranes. The positive effect of EBR remained after soybean rehydration. Plants treated with EBR showed better recovery with greater plant height, leaf area, lower number of aborted grains, in addition to an increase in stem (37.2%), root (62.8%), leaf (51.8%) dry matter and 1000 seed weight (33%) compared to plants without EBR. This information suggests that EBR not only mitigated the deleterious effect of drought stress but also improved plant growth and yield post‐stress.