Induction of HCO3− Transporting Capability and High Photosynthetic Affinity to Inorganic Carbon by Low Concentration of CO2 in Anabaena variabilis

Abstract

The apparent affinity of photosynthesis for inorganic carbon in Anabaena variabilis strain M-3 increased during the course of adaptation from high to low CO₂ concentration (5% and 0.03% v/v CO₂ in air, respectively). This was attributed to an increased ability of the cells to accumulate inorganic carbon during the course of adaptation to low CO₂ conditions. The release of phycobiliproteins was used to evaluate the sensitivity of the cells to lysozyme treatment followed by osmotic shock. High CO₂-grown cells were more sensitive to this treatment than were low CO₂ ones. The efflux of inorganic carbon from cells preloaded with radioactive bicarbonate is faster in high than it is in low CO₂-adapted cells. It is postulated that the cell wall or membrane components undergo changes during the course of adaptation to low CO₂ conditions. This is supported by electron micrographs showing differences in the cell wall appearance between high and low CO₂-grown cells. The increasing ability to accumulate HCO₃⁻ and the lessened sensitivity to lysozyme during adaptation to low CO₂ conditions depends on protein synthesis. The increase in affinity for inorganic carbon during the adaptation to low CO₂ conditions is severely inhibited by the presence of spectinomycin. Incubation in the light significantly lessens the time required for the adaptation to low CO₂ conditions.