PHOTOOXIDATIVE DAMAGE TO THE CYANOBACTERIUM SPIRULINA-PLATENSIS MEDIATED BY SINGLET OXYGEN

Experiments on the specific growth rate, bleaching of pigments, O-2 ev olution, lipid peroxidation, and loss of sulfhydryl (- SH) content in response to the varying light intensities (2-28 W/m(2)) suggested that photodamage to the Spirulina cells was maximum at or beyond the photo synthesis saturating light intensity (12 W/m(2)). However, photobleach ing of the chlorophyll a was relatively higher than beta carotenoid. T he results on the N,N-dimethyl-p-nitrosoaniline (RNO) bleaching in the presence of oxygen radical quenchers exhibited maximum effect of sodi um azide and indicated about the generation of singlet oxygen. The chl orophyll a-sensitized production of singlet oxygen by a type II reacti on cannot be ruled out because of maximum oxidative damage to the cell s at or beyond the photosynthesis saturating light intensity, i.e., 12 W/m(2), when the availability of triplet chlorophyll is maximum.