Polypeptide Rapid Turnover and Photosystem II Recovery from Calcium Stress in Anacystis Nidulans

Abstract

When liquid cultures of cyanobacteria are illuminated in medium devoid of Ca²⁺ , then Photosystem II (PS II) activity becomes totally inhibited within a few h. Addition of Ca²⁺ to the growth medium fully restores activity anc cells resume normal growth (1). Partial electron transport activities of membranes isolated from broken cells indicate a site of inhibition very near to the reaction center of PS II (2). This site is also indicated by measurements of fluorescence induction kinetics and ms delayed fluorescence (3). Calcium depletion appears to switch off PS II units on an all-or-none basis, rather than gradually slowing down their turnover rate (2). Both inhibition in the absence of Ca²⁺, and recovery upon addi-tion of Ca to the culture are light dependent. Here we report on evidence for light-dependent turnover of PS II polypeptide, and the effect of Ca²⁺ on this turnover.