Progesterone increases photochemical efficiency of photosystem II in wheat under heat stress by facilitating D1 protein phosphorylation

Experiments were conducted to investigate the effects of exogenous progesterone on photochemical efficiency of PSII and turnover of D1 protein under heat stress during the grain-filling stage. Heat stress resulted in increases of hydrogen peroxide production, malondialdehyde content, and relative electrolytic leakage in wheat leaves, but these responses were alleviated by foliar application of progesterone. Meanwhile, activities of superoxide dismutase, catalase, and peroxidase were significantly improved in progesterone-pretreated leaves. Along with the alleviation of oxidative stress, higher abundances of STN8 and phosphorylated D1 protein and lower total D1 protein content in the PSII reactive center were observed in progesterone-pretreated leaves relative to controls. Consequently, progesterone raised the potential photochemical efficiency, actual photochemical efficiency, and electron transfer rate. These results indicate that foliar application of progesterone can effectively alleviate heat-induced PSII damage by enhancing antioxidant capability and regulating phosphorylation of D1 protein in wheat leaves.