Kinetics of chlorophyll fluorescence at 77K in Chlorella and chloroplasts. Effects of CCCP, ferricyanide and DCMU.

The kinetics of chlorophyll fluorescence at 77K were studied in Chlorella cells and spinach chloroplasts. During a first illumination, the rise is polyphasic with at least three phases. The slowest one is irreversible and corresponds to the cytochrome oxidation. The dark regeneration of half the variable fluorescence is biphasic, the fast phase being inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) both in Chlorella and chloroplasts. The fluorescence rise during a second illumination is still biphasic. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) slows down the fluorescence rise in Chlorella but has no effect on the dark regeneration. It does not affect the fluorescence of chloroplasts. Ferricyanide which oxidizes cytochrome beta-559 at room temperature produces a quenching of the variable fluorescence and an acceleration of the fluorescence rise during the first illumination. Our results fit the idea of the heterogeneity of the Photosystem II centers at low temperature.