Effects of Brassinosteroids on Photosynthetic Performance and Nitrogen Metabolism in Pepper Seedlings under Chilling Stress

Abstract

To investigate the effects of brassinosteroids on plant growth and nitrogen metabolism in pepper seedlings under chilling stress, pepper seedlings with three true leaves were foliar pretreated with 0.1 μM exogenous 24-epibrassinolide (EBR) before carrying out chilling stress for 7 days. The results showed that perapplication of EBR mitigated the chill-induced decrease in plant growth via maintenance of a high net photosynthetic rate (Anet), maximum quantum efficiency (Fv/Fm), and photochemical quenching coefficient (qP). Exogenous EBR markedly increased the levels of partial free amino acids (proline, arginine, aspartic acid, and glycine) and promoted nitrogen metabolism through increasing the activities of nitrate reductase (NR), glutamine synthase (GS), glutamate synthase (GOGAT), and glutamate dehydrogenase (GDH) in the leaves of pepper seedlings under chilling stress. The effect of exogenous EBR on the content of reactive oxygen species was also investigated. Pretreatment with EBR reduced the accumulation of hydrogen peroxide (H2O2) and superoxide anion (O2−·), and concomitantly alleviated membrane lipid peroxidation of pepper leaves under chilling stress. These results suggest that foliar pretreatment of EBR has a positive effect on improving the chilling tolerance of pepper seedlings via maintaining a high photosynthetic capability and enhancing the nitrogen metabolism.