Interacting effects of radiation and temperature on chlorophyll fluorescence and D1 protein in Satsuma mandarin plants.

Interacting effects of high temperature of 30℃ and high radiation of 1300 μmol·m-2·s-1 on characteristic of the chlorophyll fluorescence and level of the D1 protein in three-year-old Satsuma mandarin (Citrus unshiu Marc.) plants were investigated by the chlorophyll fluorescence, SDS-PAGE and Western-blotting analysis. The results show that contents of total chlorophyll and chlorophyll a, and the chlorophyll a to chlorophyll b ratio in leaves declined markedly under conditions of interaction of high radiation and high temperature for 50 days, while change of the chlorophyll b is not prominent. The initial fluorescence (Fo) increased, photochemical efficiency of PSII (Fv/Fm), photochemical quenching (qP) and electron transport capacity (ΦPS Ⅱ) declined significantly in high irradiation and high temperature treatment plants. Moreover, non-photochemical quenching (qN, reflecting heat dissipation) increased. In addition, light saturation point in response of apparent electron transport rate (ETR) to light intensity and slope of the ETR to photo flux density (PFD) in range of less than 200 μmol·m-2·s-1 decreased. Fast phase of chlorophyll fluorescence kinetics showed that (Fi-Fo) to (Fp-Fo) ratio reflecting activation of QA reduction declined, contrarily, slope of Fi to Fp reflecting proportion of inactive PS Ⅱ reaction centers increased. Otherwise, synthetic rate of the D1 protein was slower than its degradation rate resulting in a net reduced content of the D1 protein. These results suggested that under the interaction of high radiation and high temperature conditions, the D1 protein synthesis was inhibited which led to inactive PS Ⅱ reaction centers, decreased the electron transport and the photochemical efficiency of PS Ⅱ.