Gg. Bozzo et B. Colman, The induction of inorganic carbon transport and external carbonic anhydrase in Chlamydomonas reinhardtii is regulated by external CO2 concentration, PL CELL ENV, 23(10), 2000, pp. 1137-1144
Induction of the carbon concentrating mechanism (CCM) has been investigated
during the acclimation of 5% CO2-grown Chlamdomonas reinhardtii 2137 mt cells to well-defined dissolved inorganic carbon (C-i) limited conditions.
The CCM components investigated were active HCO3- transport, active CO2 tra
nsport and extracellular carbonic anhydrase (CA(ext)) activity The CA(ext)
activity increased 10-fold,within 6 h of acclimation to 0.035% CO2 and ther
e was a further slight increase over the next 18 h. The CA(ext) activity al
so increased substantially after an 8 h lag period during acclimation to ai
r in darkness, Active CO2 and HCO3- uptake by C, reinhardtii cells were ind
uced within 2 h of acclimation to air, but active CO2 transport was induced
prior to active HCO3- transport. Similar results were obtained during accl
imation to air in darkness. The critical C-i concentrations effecting the i
nduction of active C-i transport and CA(ext) activity were determined by al
lowing cells to acclimate to various inflow CO2 concentrations in the range
0.035-0.84% at constant pH, The total C-i concentration eliciting the indu
ction and repression of active C-i transport was higher during acclimation
at pH 7.5 than at pH 5.5, but the external CO2 concentration was the same a
t both pHs of acclimation. The concentration of external CO2 required for t
he full induction and repression of C-i transport and CA(ext) activity were
10 and 100 mu M, respectively. The induction of CA(ext) and active C-i tra
nsport are not correlated temporally, but are regulated by, the same critic
al CO2 concentration in the medium.