Soybean Seed Priming with Brassinosteroids Mitigates the Effects of Drought Stress

Globally, drought is one of the most harmful abiotic factors to plant physiology and production, including soybean. Although 24-epibrassinolide (EBL), an important new plant hormone, can mitigate its negative impacts, the effect of EBL depends on the concentration used. The aim of the present study was to assess the effect of different EBL concentrations on the seed priming of two soybean varieties submitted to drought stress. A randomized block design with a three-way factorial scheme was used (2 x 5 x 2). The factors corresponded to two water regimes, well-watered plants (soil moisture at 100% field capacity) and drought stress (total suspension of irrigation until 20% field capacity), with five EBL concentrations in seed priming (0, 0.05, 0.10, 0.15, and 0.20 mu M) and two soybean varieties (Don Mario 82K84 and Mamor & eacute; IPRO). Drought, particularly severe drought stress, reduced gas exchange, relative water content (RWC) and dry matter production, and increased leaf temperature and proline content. However, 0.05 and 0.10 mu M of EBL minimized the effect of drought stress on gas exchange, RWC and cumulative dry matter reduction, besides decreasing leaf temperature and proline content. Priming soybean seeds with 0.05 and 0.10 mu M EBL and subsequently exposing the plants to drought stress mitigates the impacts of this stress, improving the leaf photosynthetic rate and increasing water use efficiency and dry matter production. This study demonstrates the importance of priming soybean seeds with EBL to mitigate drought stress, providing new insight on a topic that requires further research.