RESPONSE OF CATALASE ACTIVITY TO ENVIRONMENTAL-STRESS IN THE FRESH-WATER DINOFLAGELLATE PERIDINIUM-GATUNENSE

Catalase activity increased in Peridinium gatunense (formerly P. cinct um fa. westii) cells during the decline of the seasonal spring bloom p eriod in Lake Kinneret. This was correlated with the low ambient total CO2 concentration. The relationship was confirmed in laboratory exper iments where maximum catalase activity occurred under an atmosphere co mposed of 30% O2 and 0.003% CO2. Conversely, high CO2 concentrations i nhibited catalase activity. The rise in catalase activity was not dire ctly due to increasing environmental pH, as in vitro and in vivo measu rements showed a characteristic broad pH curve with a constant activit y from pH 6-10 for catalase. Photoinhibition of catalase occurred abov e 250 mumol photons.m-2.s-1. However, at high photoinactivating irradi ances, photoinhibition was ameliorated under high pO2/pCO2. Such condi tions prevail in the Kinneret at the end of the spring. We propose tha t the enhancement of photorespiration (under high pO2/pCO2) induces a temporary burst in catalase activity despite the progressively photoin hibitory conditions of early summer.