The effect of blue and red light on the adaptation to low CO2 conditions was studied in high-CO2 grown cultures of Chlorella Pyrenoidosa (82T) and Chlamydomonas reinhardtii(137+) by measuring O2 exchange under various inorganic carbon (Ci) concentrations. At equal photosynthetic photon flux density (PPFD), blue light was more favourable for adaptation in both species, compared to red light. The difference in photosynthetic oxygen evolution between cells adapted to low Ciunder blue and red light was more pronounced when oxygen evolution was measured under low Ci compared to high Ci conditions. The effect of light quality on adaptation remained for several hours. The different effects caused by blue and red light was observed in C. pyrenoidosa over a wide range of PPFD with increasing differences at increasing PPFD. The maximal difference was obtained at a PPFD above 1 500 μmol m−2s−1. We found no difference in the extracellular carbonic anhydrase activity between blue- and red light adapted cells.
The light quality effect recorded under Ci-limiting conditions in C. reinhardtii cells adapted to air, was only 37% less when instead of pure blue light red light containing 12.5% of blue light (similar PPFD as blue light) was used during adaptation to low carbon. This indicates that in addition to affecting photosynthesis, blue light affected a sensory system involved in algal adaptation to low Ci conditions. Since the affinity for Ci of C. Pyrenoidosa and C. reinhardtii cells adapted to air under blue light was higher than that of cells adapted under red light, we suggest that induction of some component(s) of the Ci accumulating mechanism is regulated by the light quality.