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Exogenous spray application of 24-epibrassinolide induced changes in photosynthesis and anti-oxidant defences against chilling stress in eggplant (Solanum melongena L.) seedlings

Summary Brassinosteroids (BRs) have been implicated in the responses of plants to various environmental stresses.To explore the mechanism(s) of BRs in the tolerance of plants to low temperatures, 24-epibrassinolide (EBR)-induced changes in chlorophyll concentrations, gas exchange parameters, chlorophyll fluorescence, and anti-oxidant defence systems in eggplant (Solanum melongena L.) were studied under chilling stress conditions. Seedlings were exposed to 10°C/5°C (day/night) chilling temperatures for 8 d, with or without a single spray of 0.1 ?M EBR applied 24 h beforehand.The EBR treatment partially overcame the inhibition of growth caused by 8 d of chilling stress.The application of EBR to chilled seedlings had a significant effect on photosynthesis, as reflected by increases in the concentrations of chlorophyll a, chlorophyll b, and total chlorophyll, the net photosynthetic rate (Pn), stomatal conductance (gs), the quantum efficiency of PSII (Fv/Fm), the efficiency of the excitation capture of open PSII centres (Fv'/Fm'), the quantum yield of PSII (_PSII), and the photochemical quenching coefficient (qP). Moreover, pre-treatment with EBR alleviated chilling-induced oxidative damage, as shown by significantly lower concentrations of reactive oxygen species and reduced membrane lipid peroxidation. EBR also caused increases in the activities of superoxide dismutase, guaiacol peroxidase, catalase, and ascorbate peroxidase, and in the concentrations of ascorbic acid, reduced glutathione, and proline in seedlings grown under chilling stress. These results suggest that the protective role of EBR against chilling stress in eggplant may be associated with an increased photosynthetic capacity and an improved anti-oxidant defence system throughout the 8 d chilling period.