ROLE OF DARK RESPIRATION IN PHOTOINHIBITION OF PHOTOSYNTHESIS AND ITSREACTIVATION IN THE CYANOBACTERIUM ANACYSTIS-NIDULANS

Photoinhibition of photosynthesis and its reactivation was studied in the cyanobacterium A. nidulans in the presence of the respiratory inhi bitor sodium azide, the uncouplers carbonyl cyanide p-(trifluoromethox y)-phenylhydrazone (FCCP) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) and the photosystem I elicitor phenazine methosulphate (PMS). Inhibition of dark respiration by azide increased the susceptibility o f the cyanobacterium to photoinhibition. Both FCCP and CCCP also remar kably affected the process of photoinhibition in A. nidulans. The PMS at lower photoinhibitory light intensity partially protected A. nidula ns from photoinhibition. The recovery from photoinhibition in the pres ence of azide or FCCP was slow and normal photosynthesis could not be resumed even after a longer period of incubation under suitable reacti vating condition. Thus dark respiration has a key function in the proc ess of photoinhibition of photosynthesis and its reactivation in the c yanobacterium A. nidulans.