Abstract
Chlamydomonas cells utilize inorganic carbon very efficiently and suppress photorespiration by the operation of CO2-concentrating mechanism (CCM) when adapted to limiting CO2. Only limited number of CCM mutants are available, and their photosynthetic characteristics are still not fully investigated. To help understand the CCM, photosynthetic characteristics of the mutants, ca1, which over-accumulates DIC in the cells but cannot utilize, and pmp1, which cannot accumulate DIC, are compared with wild type and RPR1, a mutant with reduced rate of photorespiration. NPQ around CO2-compensaton point was about 0.6 in 5% CO2-grwon cells of all strains studied. On the other hand, in air (300 ppm CO2)-adapted cells, NPQ was much higher in ca1 than that of wild type and RPR1 (about 1.5), and was as low in pmp1 as that in 5% CO2-grown cells. In addition, a partial operation of DIC transport was suggested only at very low DIC concentrations in air-adapted cells.
