Changes in Malate Content and in Enzymes Involved in Dark CO2 Fixation during Growth of Acer pseudoplatanus Cells in Suspension Culture

It has been reported in some cases that an increase in pCO₂ stimulates growth in diluted cell suspension cultures. Experiments have been designed to study the pattern of dark CO₂ fixation in sycamore cells grown in liquid suspension and to correlate this pattern with the culture growth phases. Comparisons were made between enzymatic activities, CO₂ incorporation, malic acid content during lag, logarithmic and stationary phases of growth. Malic enzyme (NADP-dependent) was at its maximum activity during early logarithmic growth phase, when biosynthetic capacities were at the highest. Phosphoenolpyruvate-carboxylase activity was strongly correlated with the ability of cells to fix CO₂. Malic acid content decreased soon after transfer of the cells to a new medium and increased at the onset of stationary phase. Under optimal conditions, the CO₂ incorporation pattern did not change during growth, with an almost identical incorporation in the basic (amino acids) and acidic (organic acids) fractions. These observations have been discussed in relation to a possible effect of increased pCO₂ in the cell environment.