Effects of high-CO2 stress on photosystem II in a green alga, Chlorococcum littorale, which has a tolerance to high CO2

A green alga, Chlorococcum littorale, is known to have a tolerance to high CO2 conditions. By a sudden change from stir to high CO2, PSII activity of C. littorale decreased temporarily and then recovered, while PSI activity showed the opposite change (Pesheva et al., Plant Cell Physiol, 35 (1994) 379-387). To investigate the efficiency of energy captured by open PSII reaction centers, the quenching of chlorophyll fluorescence of intact cells of C. littorale was analyzed. The data obtained are compared with those obtained with cells of Stichococcus bacillaris which has little tolerance to high CO2. Activities of photosynthetic oxygen evolution of the intact cells and DCIP photoreduction with the crude membrane fraction of C. littorale decreased within 1-2 days, and after about 4 days both activities recovered and/or were elevated to higher levels than those in the air conditions. During this temporal decrease in these activities, the effective quantum yield of PSII also lowered to about 50% of that in air. The values of F-v/F-m transiently decreased indicating photoinhibition in PSII. Such fluorescence quenching parameters recovered after about 4 days. On the other hand, the activities of PSII and other photosynthetic characteristics did not recover in S. bacillaris.