The response of Synechococcus PCC7942 (Cyanophyta) to changes in CO2 supply in relation to the acclimation of the CO2-concentrating mechanism. I: physiological study

Cultures of Synechococcus PCC7942 growing in BG11 medium, Hepes 20 mmol/L, pH 7.8, 100 . mu mol .m(-2).s(-1) continuous light, experienced inorganic c arbon (C-1) limitation las indicated by a decrease in growth rate) when shi fted from high-CO2 to ordinary air under conditions of active bubbling. The high-affinity state of the carbon-concentrating mechanism (CCM), evaluated as K-0.5(C-1), was induced to the same extent under conditions of C-1 limi tation imposed by air or CO2-depleted air (20 muL .L-1), though it required a lag of 3 h in the first case and was immediate in the second. Dissolved inorganic carbon (DIC) in cultures transferred to air was 1.24 mmol/L (corr esponding to [HCO3-] = 1.19 mmol/L and [CO2] = 36 mu mol/L at pH 7.8) at th e time induction started. Values of the initial rate and total photosynthet ic O-2 evolution during the compensation period, and the time required to r each compensation, differed in non-induced and induced cells: O-2 evolution and time required to reach compensation were high in non-induced cells and low in induced cells, while V-0 was low in non-induced and high in induced cells. The coincident time courses of growth rate, K-0.5(C-1), V-0 of comp ensation, and total O-2 during compensation in response to changes in CO2 s upply suggested that these variables were directly related, and that an imb alance between metabolic/energetic capacity for CO2 fixation and internal C O2 availability might be involved in CCM induction under the experimental c onditions used in this study.