Activities of Enzymes of Carbohydrate Metabolism in Cells of Acer pseudoplatanus L. Maintained in Continuous (Chemostat) Culture

1 Cells of Acer pseudoplatanus were grown in an apparatus specially designed for the continuous culture of plant cells. Experiments were carried out to assess the suitability of such systems for studies on the regulation of plant cell respiration. 2 The stability of enzyme activities during the maintenance of specific growth rates (i.e. under steady state conditions) was studied and was found to be good, irrespective of whether the cells were maintained at low or high growth rates. 3 Marked changes in the relative activities of glycolytic and pentose phosphate pathway enzymes were found to occur with changes in cell growth rate. The pentose phosphate pathway enzymes showed their highest activity per cell at high growth rates (about 80 h mean generation time) and a similar situation was found for the glycolytic enzymes, pyruvate kinase and hexokinase. Phosphofructokinase however had its highest activity at medium growth rates (about 150 h). 4 Other parameters also showed marked changes with changing growth rate. Levels of oxygen uptake and protein per cell were highest at high growth rates, falling markedly with only a small decrease in growth rate (from about 80 h–100 h mean generation time). In contrast the dry weight per cell showed a continuing decrease with increasing growth rate. 5 The stability of the steady states maintained at different growth rates, the ability to alter the growth conditions in a precise way, and the marked changes occurring in respiratory parameters at different growth rates, suggest that these culture systems are ideally suited for studies of the regulation of plant cell respiration.