PHOTOSYNTHETIC CHARACTERISTICS OF PHOTOMIXOTROPHIC AND PHOTOAUTOTROPHIC CELL-SUSPENSION CULTURES OF CHENOPODIUM-RUBRUM

Cell suspension cultures of Chenopodium rubrum have been grown for more than 2 years photoautotrophically with CO2 as sole carbon source. Average increase in fresh weight is appr. 600% within 14 days. The chlorophyll content of photoautotrophic cells (200 μg/g fresh weight) is much higher than of photomixotrophic cells (50 μg/g fresh weight). The photosynthetic activity of the cells (190 μmoles CO2×mg-1 chlorophyllXh-1) is comparable to the values found with intact leaves. As shown by short-term14CO2 photosynthesis, both, the photomixotrophic and the photoautotrophic cell suspension cultures assimilate CO2 predominantly via the Calvin pathway. Major differences were found with cells from either exponential or stationary phase of growth with regard to differential labelling of 3-phosphoglyceric acid, malate, sucrose and glucose/fructose. In vitro measurements of carboxylation reactions only partially corroborate our findings with14CO2 incorporation. The ratio of ribulosebisphosphate to phosphoenolpyruvate carboxylase activity is 4.7 for leaves of C. rubrum, 1.2 for photoautotrophic cells during stationary growth and 0.5 for cells during exponential growth phase, however, 0.18 was found for photomixotrophic cells. Though the14CO2 incorporation into 3-phosphoglyceric acid is clearly higher than into malate, the in vitro activity of phosphoenolpyruvatecarboxylase is 2-6 fold higher than that of ribulosebisphosphate carboxylase. We postulate that anaplerotic reactions of the tricarboxylic acid cycle are involved in the regulation of phosphoenolpyruvate carboxylase. © 1979 Springer-Verlag.