Growth at high CO2 affects the chloroplast number but not the photosynthetic efficiency of photoautotrophic Marchantia polymorpha culture cells

Photoautotrophic suspension cells of Marchantia polymorpha were grown at gas phase CO2 concentrations of 0.4% and 2.0%. At the higher CO2 concentration the chloroplast shape appeared to be modified and the cells had about 70% more chloroplasts per cell. Differences in chlorophyll content per cell were much less pronounced, indicating a reduction in chlorophyll content per chloroplast. Also the cell size was affected by the CO;? concentration, and our data suggest that it was about 37% lower in high CO2 grown cells than in low CO2 grown cells. The capacity and the efficiency of photosynthetic oxygen evolution on a chlorophyll basis and the photosystem II chlorophyll fluorescence parameters were almost identical in both cell types. Immunodection showed that also the ratio of light harvesting complex II antenna proteins and ribulose 1,5 bisphosphate carboxylase/oxygenase were unaltered. These data indicate that the chloroplast density within photoautotrophic culture cells may be regulated independently of their photosynthetic efficiency.