Brassinosteroids (BRs) have been rarely tested for their effective roles in mitigation of deleterious effects of
water stress (WS) on plants. In addition, the contribution of
nitric oxide (NO) in BR-improved plant tolerance to
water stress needs to be elucidated. So, a trial was carried out to uncover the contribution of NO in BR-induced tolerance of pepper plants to WS. For well-watered and water-stressed plants, soil water availability was sustained at 80% and 40% of the full water storage capacity, respectively. BR (24-epibrassinolide, EB; 1.0 μM) was sprayed to the leaves of both well-watered and water stressed-pepper plants every two days for 10 days prior to the initiation of stress treatment. After starting WS treatment,
cPTIO was sprayed to plant leaves twice a week for four weeks.
Water stress caused a reduced plant growth and oxidative stress, but the application of EB increased plant growth and reversed the oxidative stress. The EB treatment increased endogenous NO and reinforced
antioxidant defence systems, but the
cPTIO application reversed the NO levels, downregulated the
antioxidant defence systems, and aggravated oxidative damages caused by WS. These results show that EB-induced NO generation and NO-mediated
antioxidant defence systems might be crucial mechanisms for EB-improved tolerance of pepper plants to WS. So, both EB and NO jointly are responsible for achieving improved tolerance of pepper plants to
water stress.