Study the effect of 24-epibrassinolide application on the Cu/Zn-SOD expression and tolerance to drought stress in common bean

To study the possibility of increasing the drought tolerance of common bean with the exogenous application of 24-epibrassinolide (EBL), an experiment was conducted in 2016 and 2017. In this experiment, two irrigation levels (optimal irrigation and drought stress) were applied to the main plots and two common bean genotypes (Kusha cultivar and COS16 genotype) and four EBL concentrations (0, 2, 4, and 6 mu M) were allocated to sub-plots as factorial. In the flowering stage, drought stress was applied and plants were sprayed with EBL. The results showed that drought stress reduced relative water content (RWC) and increased proline content, malondialdehyde (MDA) content, and antioxidant enzymes activity. However, exogenous application of EBL reduced the seed yield loss and increased the drought stress tolerance in both common bean genotypes by decreasing the MDA content and increasing the RWC, proline content, antioxidant enzymes activity, and nitrate reductase activity. It can be concluded that foliar spray of 4 mu M EBL as the best concentration may increase the seed yield and enhance the drought stress tolerance of common bean. Also, Cu/Zn-SOD was up-regulated in response to the drought stress and exogenous EBL. The COS16 genotype showed better response to the drought stress and exogenous EBL than the Kusha cultivar, because of the higher up-regulation of Cu/Zn-SOD in this genotype compared to the Kusha cultivar. Therefore, EBL can be used as a plant growth regulator to enhance drought stress tolerance and minimize the seed yield loss of common bean caused by water deficit.