Effect of the C02-Concentration during Growth on the Oxygen Evolution Pattern under Flash Light in Chlorella

Photosynthetic 0 2-evolution patterns were determined in cells of Chlorella vulgaris 211 — 11 h, grown under air enriched with 2% C 0 2 (High C 02-cells) and under ordinary air (Low C 0 2-cells). Oxygen evolution in these algae was measured as consequence of short saturating light flashes with the three electrode system according to Schmid and Thibault, Z. Naturforsch. 34c, 414 (1979). It was shown that Low CO:-cells had the usual Joliot-Kok pattern of 0 2 evolution whereas High C 0 2-cells exhibited a more reduced pattern characterized by the fact that maximal flash yield was observed under the 4th flash and that damping due to misses was more important than in Low COi-cells. Moreover, the amplitudes of the amperometric signals in High C 0 2-cells were consistently lower. The observations clearly speak in favor of a more reduced condition of the Sstate system, when the cells are grown under high C 0 2. This was confirmed by the fact that higher concentrations of hydroxylamine had to be added to bring Low C 02-cells into the maximally reduced condition namely S 2, than was the case with High C 0 2-cells. Our observations suggest that the redox condition of the S-state system of photosystem II in Chlorella vulgaris is affected either by changes of C 0 2 concentrations during algal growth or that the S-state system is only maintained in the 4 state Kok condition when the enzyme carbonic anhydrase is present.