CARBON AFFINITY ADAPTATION OF SYNECHOCOCCUS AND ITS PHYCOCYANIN MUTANT TO VARIOUS CO2 CONCENTRATIONS AND LIGHT INTENSITIES

The dependence of the photosynthetic capacity on the CO2 concentration provided was used as a measurement of the affinity of the photosynthe tic apparatus for carbon. ''Affinity'' includes uptake, transport and incorporation of inorganic carbon. The affinity of the photosynthetic apparatus for CO2 was tested in cells adapted to high and low CO2 conc entrations and light intensities. The photosynthetic capacity at satur ating concentrations of bicarbonate (V-sat) was higher for cells grown under aerated conditions with 3% CO2 (HC cells) than for those grown under aerated conditions with air (LC cells). The half-saturating bica rbonate concentration (K-1/2) was lower in LC cells than in HC cells. The effect of various light intensities on V-sat and K-1/2 during adap tation was small. Principally the same results were obtained for the w ild type and the mutant AN 112, which lacks most of the phycocyanin wi thin the phycobilisome, i.e. its light-harvesting system. This indicat es that light intensities can modulate the affinity for CO2 much less than the CO2 concentration during the adaptation process. When the CO2 concentration during adaptation of the mutant cells was reduced from 3% to the level of air, K-1/2 decreased to about 5% within a few hours , whereas V-sat approached a level of about 60% of the starting value gradually over many days. When the CO2 concentration was raised, K-1/2 began to increase after 6 h. V-sat decreased quickly and thereafter i ncreased to exceed the original level after 6 h. As a result of the ad aptation to different CO2 concentrations, the kinetics of V-sat and K- 1/2 are different. This implies that V-sat and K-1/2 are controlled by different processes.