Effects of 24-epibrassinolide and the synthetic brassinosteroid mimic on chili pepper under drought

Drought is major stress that severely reduces plant growth and productivity. To improve drought tolerance, an exogenous brassinosteroids (BRs) has been used effectively in the field condition. However, the application of BRs is expensive due to the scarcity of natural BRs and the multistep synthesis of BRs. In an attempt to reduce the cost, 7,8-dihydro-8 alpha-20-hydroxyecdysone (DHECD) has been proposed to function as an imitation of 24-epibrassinolide (EBR). In this study, chili pepper plants (Capsicum annuum L. var. frutescens (L.) Kuntze) were sprayed with DHECD, EBR at 1 A mu M or distilled water (control). Plants were subjected to severe water stress (25% pot water capacity) for 5 days and their physiological effects and yield were investigated. The result showed that the applications of DHECD and EBR before the beginning of water stress could improve leaf water status determined by relative water content in plants grown under drought condition. The electrolyte leakage, lipid peroxidation level, and H2O2 production were significantly declined, while the accumulations of proline and total soluble sugar were increased in the treated plants. Moreover, the net photosynthesis (P-N) was elevated due to the increases of stomatal conductance (g(s)) and intercellular CO2 concentration (C-i) after BR pretreatments under drought. In addition, applications of DHECD and EBR maintained all chlorophyll fluorescence parameters; F-v/F-m, F-v'/F-m', Phi PSII, qP, and ETR, to remain the photosynthesis. As a result, shoot biomass, fruit yield and capsaicin level were considerably enhanced in the treated plants. DHECD showed better performance to maintain membrane integrity; however, EBR had more effect on the osmotic maintenance. The result also showed that pretreatment with BRs had little or no effect on well-watered plants. The study concluded that DHECD and EBR alleviated the impact of drought on physiological responses and consequently minimized yield loss.