Photo-inactivation of System II centers by carbonyl cyanide m-chlorophenylhydrazone in Chlorella pyrenoidosa

Abstract In the presence of a high concentration of carbonyl cyanide m -chlorophenylhydrazone (CCCP) (4 · 10 −6 M), the S 2 and S 3 dark decays are accelerated and become biphasic with a first half-time of 0.6 s. The first fast phase of the decays does not correspond to a simple reduction of S 2 , S 3 back to S 0 , S 1 (i.e. to an acceleration of the deactivation reaction), but to a decrease in the number of oxygen-evolving System II centers. This photo-inactivation produced by CCCP is rapidly reversible in the dark.