EFFECTS OF TEMPERATURE ON SYNECHOCYSTIS SP. R10 (CYANOPROKARYOTA) AT TWO IRRADIANCE LEVELS. I. EFFECT ON GROWTH, BIOCHEMICAL COMPOSITION AND DEFENSE ENZYME ACTIVITIES

Summary. The infl uence of fi ve different temperatures (20, 26, 32, 39 and 44°С) under two irradiance levels (132 µmol photons m -2 s -1 , unilateral and 2×132 µmol photons m -2 s -1 , bilateral) on the growth, biochemical composition and enzymatic antioxidant defense of a newly isolated unicellular Synechocystis sp. strain R10 was studied. This photoautotrophic blue-green alga grew well in the temperature range 26-39°C under lower light intensity, but the cultures could grow, although slower, at 20°C and 44°C. Temperature, under higher irradiance level, did not signifi cantly affect the growth, except for 44°C, where the growth was greatly reduced. Synechocystis sp. R10 responded to the unfavorable conditions by changes in its biochemical composition and enzyme activities. At 20°C and lower light, total carbohydrates content as well as the activities of superoxide dismutase, catalase, glutathione reductase and defi ned protease isoforms were increased. The response to the combination of high temperature (44°C) and lower light consisted in accumulation of carotenoids and C-phycocyanin, but not in the induction of antioxidant enzymes activity. A signifi cant enhancement in carbohydrate content was observed at 44°C and higher light, simultaneously with the reduction in protein content and activity of all studied enzymes. The observed modulation of antioxidant enzyme and protease activities, and changes in carbohydrate and pigment contents could be a prerequisite for the thermal tolerance and ability of the cyanobacterium to adapt to different environment. Because of its fast growth rate, high phycobiliprotein, carbohydrate and protein contents, and wide adaptability, this strain is of biotechnological interest.