INACTIVATION OF PHOTOSYSTEM-II IN THE PROCESS OF HETEROTROPHIC GROWTH IN CHLORELLA

In the absence of light, adding glucose to a Chlorella culture (Chlorella vulgaris B.) in a mineral medium causes cell growth and inactivation of photosystem II (PSII). The latter circumstance is manifested in increase in the yield of constant fluorescence of chlorophyll (Chl) and appearance of a slow (approximately 1.5 nsec) component in the kinetics of its quenching, suppression of variable fluorescence, increase in the contribution of short waves in the spectrum of low-temperature fluorescence, and increase of saturating light intensity for delayed fluorescence measured in the presence of diuron. It is concluded that inactivation of PSII during heterotrophic growth is similar to the previously detected inactivation of it in autotrophic algal culture caused by mineral nutrition deficit: PSII reaction centers in both cases lose the capacity for photosynthetic quenching of excitation energy.