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Exogenous 24-epibrassinolide alleviates the detrimental effects of suboptimal root zone temperature in cucumber seedlings

ABSTRACT Suboptimal root zone temperature (RZT) is major hurdle for vegetables production that causes a remarkable reduction in growth and yield during winter and early spring. The aim of this study is to assess the effects of 24-epibrassinolide (EBR) on physiological and biochemical mechanism on cucumber seedling under suboptimal RZT. The treatments were NT (normal RZT [22 ± 2°C]), LT (suboptimal RZT [14 ± 2°C]), EBR (0.1 µM EBR + suboptimal RZT [14 ± 2°C]) and BZR (brassinazole, a specific EBR biosynthesis inhibitor) (4 µM BZR + suboptimal RZT [14 ± 2°C]). The results showed that LT and BZR significantly decline cucumber seedlings growth, chlorophyll (Chl) contents, photosynthetic capacity, antioxidant enzyme activities and nutrients accumulation. Exogenous EBR application significantly enhanced cucumber seedling growth, Chl contents, photosynthetic capacity, nutrient contents, activities of antioxidant enzymes and reduced the contents of H2O2 (hydrogen peroxide), (superoxide radical) and malondialdehyde. The transcript levels of EBR-biosynthesis genes are reduced by LT, while reported significantly higher in EBR treated seedling. Our results suggest that exogenous EBR could alleviate the harmful effects of suboptimal RZT by modulating EBR-biosynthesis genes expression and antioxidant, nutrient, Chl and photosynthetic machinery, thus leading to improved plant growth.