ESTIMATION OF GROWTH-YIELD AND MAINTENANCE COEFFICIENT OF PLANT-CELL SUSPENSIONS

Methodology is presented for the determination of growth yield (Y(g)) and maintenance coefficient (m) for carbon utilization of plant cells grown in suspension culture. Estimation of Y(g) and m requires measurements of specific growth rate (mu) and specific rate of substrate uptake (q) at different growth limiting substrate concentrations. Batch culture of tobacco cells did not permit evaluation of Y(g) and m because mu is constant and maximal during most of the growth cycle. In batch culture, the period of declining specific growth rate is extremely brief because of the rapid transition from logarithmic growth to stationary phase. This occurs because the k(m) for growth is relatively small compared to the initial sucrose concentration. Thus, when the substrate level reaches the k(m), the large mass of cells rapidly depletes the remaining substrate. In contrast, semicontinuous culture facilitates the determination of Y(g) and m because various steady-state growth rates can be achieved. Mathematical expressions were developed to determine the effective values of mu and q over the semicontinuous replacement interval. The validity of this approach was verified by conducting simulations using experimentally determined parameters.