Altered phosphorus concentration, oxygen supply rate, and programmed addition of sucrose and phosphorus were applied to Dioscorea deltoidea plant cells in airlift suspension to increase the formation of the secondary metabolite diosgenin. A low oxygen supply rate (k$' of 3.9 h-') completely inhibited formation of diosgenin. A high oxygen supply rate (k,a' of 17.1 h-'1 led t o the greatest formation of diosgenin in 30 g/L sucrose when the sucrose-to-phosphorus mole ratio was 42.5: 1. Programmed addition of nutrients over a 15-day period reduced growth of cell mass relative t o diosgenin mass.
Intentional aggregation by entrapment of virtually all cells in reticulated polyurethane foam led to reduced cell-mass yield, diosgeninl yield and concentration relative to suspended cells at the same conditions. Entrapment of a small fraction of the cells led to a delayed development of a suspension culture and to formation of significantly higher concentrations of diosgenin.
Nearly all of this increasle was attributable t o the suspended cells. This result suggested sequestering of nonproductive cells by t h e m a t r i x o r sequestering of important nutrients by the matrix-bound cells. Entrapped cells attained densities of 40 g/L in the matrix.