24-Epibrassinolide in the Flowering Stage Mitigates the Effects of Temporary Drought Stress and Favors the Post-stress Recovery in Soybean

Foliar application of 24-epibrassinolide (EBL) has been used in different crops to reduce the adverse effects of water stress, but no studies have been found with soybean crop in the flowering stage, involving this bioregulator. Thus, this work aimed to evaluate the efficiency of the 24-epibrassinolide on growth, physiological mechanisms and antioxidant defense in soybean in the flowering phase under drought stress and rehydration. The EBL mitigated the effect of water stress on the shoot growth of soybean plants. In irrigated plants, EBL promoted improvements in gas exchange, photosynthetic efficiency, chlorophyll synthesis, and increase in shoot biomass. Plants under water deficit treated with EBL showed reductions in stomatal conductance and photosynthesis similar to those found in plants without EBL. However, the EBL mitigated the damage caused by water deficit in soybean, which was evidenced by the reduction of physiological damage to relative water content, leaf water potential, and effective equantum efficiency of photosystem II (phi(PSII)). In addition, EBL minimized oxidative stress in plants, stimulating greater activities of the antioxidant enzymes catalase (CAT) and ascorbate peroxidase (APX),lower electrolyte leakage, and lipid peroxidation, which contributed to the lower degradation of chlorophylls. The EBL contributed with the higher production of dry matter and grain production in plants subjected to stress followed by rehydration. This set of information suggests that EBL not only partially alleviated the deleterious effect of drought stress on soybean in the flowering stage, but also participated in the post-stress recovery of soybean plants, which promoted increased growth, dry matter, and yield.