Calcium contributes to photoprotection and repair of photosystem II in peanut leaves during heat and high irradiance

In this study, we investigated the effects of exogenous calcium nitrate on photoinhibition and thylakoid protein level in peanut plants under heat （40 ℃） and high irradiance （HI） （1,200 mmol/m2 per s） stress. Compared with control seedlings （cultivated in 0 mmol/L Ca（NO3）2 medium）, the maximal photochemical efficiency of photosystem II （PSII） in Ca2t‐treated plants showed a slight decrease after 5 h stress, accompanied by lower degree of PSII closure （1‐qP）, higher non‐photochemical quenching, and lower level of membrane damage. Ca2t inhibitors were used to analyze the varieties of antioxidant enzymes activity and PSII proteins. These results indicated that Ca2t could protect the subunits of PSII reaction centers from photoinhibition by reducing the generation of reactive oxygen species. In the presence of both ethyleneglycol‐bis（2‐aminoethylether）‐tetraacetic acid and ascorbic acid （AsA）, the net degradation of the damaged D1 protein was faster than that only treated with AsA. Our previous study showed that either the transcriptional or the translational level of calmodulin was obviously higher in Ca2t‐treated plants. These results suggested that, under＆amp;nbsp;heat and HI stress, the Ca2t signal transduction pathway can al eviate the photoinhibition through regulating the protein repair process besides an enhanced capacity for scavenging reactive oxygen species.