Seasonal Effects on Photosynthetic Electron Transport and Fluorescence Properties in Isolated Chloroplasts of Pinus silvestris

Abstract

AbstractChloroplasts were isolated from primary needles of 1‐year‐old seedlings and from secondary needles of a 20‐year‐old pine tree in a natural stand. In autumn the electron transport capacities of PSII, PSI and PS (II + I) decreased and the electron transport between PSII and PSI became inhibited in October in the 20‐year‐old tree. This inhibition lasted until May the following year. The partial reactions of PSI and PSII still showed low but fairly constant rates during the whole winter seedlings. Seasonal changes in the electron transport properties of 1‐year‐old showed the same general trends as observed in the 20‐year‐old tree, but the changes were less pronounced. However, in snow‐covered seedlings the PSI‐mediated electron transport and the electron transport from H2O to NADP increased during the late winter when the seedlings were still covered by snow. The total chlorophyll content of the needles decreased in autumn and winter. Low temperature fluorescence ratios of F692/F680 and F726/F680 indicated more severe destruction of the chlorophyll a antennae closely associated with the two photosystems than of the light harvesting chlorophyll a/b complex. In this case, too, the changes were more pronounced in the 20‐year‐old tree than in the 1‐year‐old seedlings. The chlorophyll/P700 ratios indicated a more marked reduction in the reaction centre molecules during autumn than in the antennae chlorophyll molecules. The changes in electron transport and low temperature fluorescence properties which occurred during autumn and winter were mainly reversed during spring.