Effect of aminooxyacetate, an inhibitor blocking the glycolate pathway, on the induction of a CO₂-concentrating mechanism and low-CO₂-inducible polypeptides in Chlamydomonas reinhardtii (Chlorophyta)

Abstract

Polypeptides of 21, 36 and 37 kDa are induced in the unicellular green alga Chlamydomonas reinhardtii when cells are transferred from high (5%) to low (0·03%) CO₂ concentrations. The synthesis of these polypeptides is correlated with the induction of the CO₂-concentrating mechanism. Interaction between the induction of low-CO₂-inducible polypeptides, the CO₂-concentrating mechanism and photorespiration has been studied in wild-type C. reinhardtii with the aim of clarifying whether the glycolate pathway is involved in algal acclimation to limiting CO₂ conditions. Our results showed that the induction of the 37 kDa periplasmic carbonic anhydrase and 21 kDa polypeptide under low-CO₂ conditions was not observed in the presence of aminooxyacetate, an inhibitor which completely blocks glycolate metabolism. However, the induction of the 36 kDa polypeptide was not affected by this inhibitor. The presence of aminooxyacetate during the acclimation to low CO₂ conditions also inhibited the increase in the photosynthetic affinity for inorganic carbon shown by low-CO₂-acclimated Chlamydomonas cells without the inhibitor. Our results suggest that the induction of the CO₂-concentrating mechanism may require the function of the glycolate pathway. In addition, our results also indicate that there is differential regulation of the induction of these three low-CO₂-inducible polypeptides in Chlamydomonas reinhardtii.