Light Requirement for Carbonic Anhydrase Induction in Chlamydomonas reinhardtii

Abstract
The regulation of carbonic anhydrase (CA) activity by light was determined for Chlamydomonas reinhardtii. When high-CO2 (4-5% CO2 grown cells were transferred to low-CO2 condition (0.04% CO2, the induction of CA activity showed correlation with the energy fluence rate. Addition of 10 μM DCMU immediately after transferring to low-CO2 condition completely suppressed the induction of CA activity, while its addition one hour after air induction still caused an increase for a while. These results indicate that there are two light-requiring steps controlling CA induction in C. reinhardtii: a photosynthesis-dependent step followed by a photosynthesis-independent one. The latter step showed requirement for blue light but not for red light. Inhibitor experiments suggest that blue light exerted its regulatory effect on the post-transcriptional level of CA biosynthesis.