PHOTOSYNTHETIC CHARACTERISTICS OF 3 STRAINS OF CYANOBACTERIA GROWN UNDER LOW-CO2 OR HIGH-CO2 CONDITIONS

Quantum requirements of photosynthetic oxygen evolution at 679 nm, flu orescence emission spectra at liquid nitrogen temperature (77 K) and f luorescence induction kinetics in the presence of DCMU, were measured in the cyanobacteria Anabaena variabilis M3, Anabaena variabilis ATCC 29413 and Anacystis nidulans R2, each grown under low- or high-CO2 con ditions. Low-CO2 grown cells of the cyanobacteria showed a higher quan tum requirement of photosynthetic oxygen evolution and a higher ratio of F-710-740 to F-680-700 fluorescence and a lower variable fluorescen ce in the presence of DCMU than high-CO2 grown cells. These findings i ndicate a change in excitation energy distribution in favour of photos ystem I. The result might be an enhancement in ATP formation caused by cyclic electron now which in turn provokes dissolved inorganic carbon (DIG) accumulation in these low-CO2 grown cells.