SUPEROXIDE-DISMUTASE ACTIVITY IN PERIDINIUM-GATUNENSE IN LAKE KINNERET - EFFECT OF LIGHT REGIME AND CARBON-DIOXIDE CONCENTRATION

The activity of super oxide dismutase (EC 1.15.1.1, superoxide: supero xide oxidoreductase) (SOD) was deter mined in Peridinium gatunense Lem m. under natural and controlled conditions. SOD activity increased tow ard the end of the spring algal bloom in Lake Kinneret simultaneously with maximal photosynthetic activity and conditions of elevated ambien t stress such as high irradiance. Activity staining of native polyacry lamide gel electrophoresis gels of bloom samples showed a similar patt ern to the spectrophotometrically measured SOD. Both Mn SOD and CuZn S OD were present, however no Fe SOD was found in Peridinium. One of thr ee isoenzymes of Mn SOD showed marked differential regulation of activ ity under stress. An increase in the quantity of the 32-kDa Mn SOD pol ypeptide during the bloom was found to be unrelated to senescence; it was assumed that this polypeptide was induced by stress. Thus, SOD in Peridinium undergoes physiological and molecular acclimation to season al environmental changes. When Peridinium was exposed to various O-2 a nd CO2 concentrations in culture, CuZn SOD significantly increased und er high CO2 concentrations and normoxic conditions (20% O-2). However, at high irradiances, Peridinium cultures exposed to low and high CO2 concentrations also had similar CuZn SOD activity. It was concluded th at stressful irradiance is the overriding cause of increased SOD activ ity in both lake samples and in cultures of Peridinium.