Involvement of photorespiration and glycolate pathway in carbonic anhydrase induction and inorganic carbon concentration in <i>Chlamydomonas reinhardtii</i>

Abstract

Interaction between induction of carbonic anhydrase (CA) activity, induction of inorganic carbon (C i ) concentrating mechanisms and the photorespiratory glycolate pathway has been studied in wild type 6145c and photorespiratory mutant 18–7F (low in phosphoglycolate phosphatase activity) cells of C. reinhardtii . Cell transfer from high CO 2 (5%, v/v) to low CO 2 (0.03%) provoked an increase of extracellular and total (extracellular plus intracellular) CA in both wild type and mutant cells. During adaptation to low CO 2 conditions, both strains excreted ammonium to the medium at a similar rate in the presence of l ‐methionine‐ d‐l ‐sulfoximine (MSX), an inhibitor of glutamine synthetase (GS). MSX also provoked ammonium excretion by air adapted wild type and mutant cells, even though both strains had high levels of CA activity and of C i concentrating activities. GS increased in both strains after transfer from high to low CO 2 conditions. However, this increase was abolished by aminooxyacetate, an inhibitor of the glyoxylate‐serine aminotransferase, and by glycolaldehyde, an inhibitor of triose phosphate to ribulose 1,5‐bisphosphate conversion. CA synthesis did not occur in the presence of either aminooxyacetate or glycolaldehyde. Algae grown in high CO 2 in the presence of aminooxyacetate did not induce C i concentrating mechanisms. Integration of these three processes, i.e., CA synthesis, C i ‐concentration, and photorespiratory glycolate pathway is proposed in the framework of carbon metabolism of the alga.