Effects of photon flux density on the ‘C02-concentrating mechanism’ of the cyanobacterium Anabaena variabilis

The effects of photon flux density on the characteristics of inorganic carbon uptake by Anabatna variabths Kütz have been investigated. Although rates of inorganic carbon transport and the affinity for inorganic carbon of hght- and Co2-dependent o2 evolution both decreased with lowered ambient photon flux density (PFD), the capacity of A. variabilis for carbon transport and CO2M accumulation was not decreased markedly by growth at low PFD. Thus the ‘CO2-concentratmg mechanism’ in Anabaena is not repressed to any great extent by growth at low rates of energy supply. These results, together with observations of the quantum requirement of cells with or without a CO2- concentrating mechanism, are discussed in relation to the energetic requirements for inorganic carbon transport in microalgae.