Effects of light on the photosynthetic apparatus and a novel type of degradation of the photosystem I peripheral antenna complexes under darkness

A novel type of degradation of photosystem I peripheral antenna complexes h as been observed in rice leaves under darkness in the present study. Photos ynthesis, chlorophyll content, the chlorophyll a/b ratio, and relative amou nts of ribulose-1,5-bisphosphate carboxylase/oxygenase decrease during dark treatment. The levels of photosystem II reaction-center complex and cytoch rome f on the basis of units of chlorophyll also decline rapidly under dark ness. In contrast, the levels of photosystem I reaction-center complex rema in stable under darkness for six days. Low-temperature fluorescence emissio n spectra ascribed to photosystem I antennae clearly show a blue shift. A s imilar shift is also observed in the photosystem I complexes resolved with dodecyl maltoside-polyacrylamide gel electrophoresis. Moreover, polypeptide analysis of the thylakoids and photosystem I complexes isolated from the g reen gels shows that some polypeptides originating from photosystem I perip heral antenna complexes disappear during the dark treatment. A curve fittin g method also displays remarkable changes in the chlorophyll components bet ween the light and dark treatments. It is likely that these results indicat e the disconnection/disassembly of the photosystem I antenna as well as the photosystem II complexes induced by dark treatment. Moreover, these findin gs also imply the existence of different degradation mechanisms for the pho tosystem I and II complexes. (C) 2000 Elsevier Science S.A. All rights rese rved.