Brassinosteroids protect photosynthesis and antioxidant system of eggplant seedlings from high-temperature stress

The effects of 24-epibrassinolide under high temperature in eggplant (Solanum melongena L.) seedlings were studied by investigating the plant growth, chlorophyll content, photosynthesis and antioxidant systems. High temperature significantly inhibited the plant growth and markedly decreased the chlorophyll content, net photosynthetic rate, stomatal conductance and transpiration rate, while it increased intercellular CO2 concentration. In a similar manner, high temperature also decreased significantly maximum quantum efficiency of PSII, potential photochemical efficiency, the quantum efficiency of PSII, photochemical quenching, the excitation capture efficiency of open centers, and increased non-photochemical quenching. Application of 0.05-0.2 mu M EBR remarkably promoted the plant growth and alleviated high-temperature-induced inhibition of photosynthesis. Under high temperature, reactive oxygen species levels and lipid peroxidation were markedly increased, which were remarkably inhibited by application of 0.05-0.2 mu M EBR. The activities of antioxidative enzymes such as superoxide dismutase, peroxidase, catalase and ascorbate peroxidase, and contents of ascorbic acid and reduced glutathione were significantly increased during high-temperature treatments, and these increases were more pronounced than those of EBR at 0.05-0.2 mu M treatment. The EBR treatment also greatly enhanced contents of proline, soluble sugar and protein under high-temperature stress. Taken together, it can be concluded that 0.05-0.2 mu M EBR could alleviate the detrimental effects of high temperatures on plant growth by increasing photosynthetic efficiency and enhancing antioxidant enzyme systems. Addition of 0.1 mu M EBR had the best ameliorative effect against high temperature, while the addition of 0.4 mu M EBR had no significant effects.