24-Epibrassinosteroid alleviate drought-induced inhibition of photosynthesis in Capsicum annuum

To investigate the role of brassinosteroids in the drought-tolerance of plants, leaf gas exchange and chlorophyll fluorescence parameters were examined in pepper (Capsicum annuum L cv. Longkouzaojiao) plants with or without 24-epibrassinolide (EBR, 0.01 mg L-1 EBR) treatment. Pepper plants were subjected to drought (45% relative soil water content, RSWC) for 10 d and then returned to well-watered conditions for 5 d. In this study, drought treatment impaired the pepper growth and reduced leaf photosynthetic rate, and drought-inhibition of photosynthesis may be due to non-stomatal factor. Drought also reduced the utilization of absorbed light energy in chloroplasts, and photoinhibition was caused by excess absorbed light energy in spite of drought-induced the increase of non-photochemical quenching coefficient (NPQ). Interestedly, EBR treatment significantly alleviated drought-induced inhibition of photosynthesis, which may be particularly attributed to the increase in capacity of CO2 assimilation and the efficiency of light utilization. EBR also significantly alleviated drought-induced photoinhibition by dissipation of excitation energy as heat from the light harvesting complex in photosystem II (PSII). We concluded that EBR could alleviate the detrimental effects of drought on photosynthesis by increasing the efficiency of light utilization and dissipation of excitation energy in the PSII antennae in leaves. (C) 2012 Elsevier B.V. All rights reserved.