METABOLIC-REGULATION IN PLANT-CELL CULTURE .34. EFFECTS OF INORGANIC-PHOSPHATE ON SUGAR CATABOLISM BY SUSPENSION-CULTURED CATHARANTHUS-ROSEUS

Several parameters of the catabolism of sugars were monitored after transfer of stationary-phase cells from suspension cultures of Catharanthus roseus to fresh complete or Pi-deficient Murashige-Skoog medium. The respiratory uptake of O2 and release of CO2 from [1-14C]- or [6-14C]glucose were always higher in the cells in the complete medium than in the cells in the Pi-deficient medium. The levels of activities of hexokinase, fructokinase, phosphofructokinase, pyrophosphate: fructose 6-phosphate 1-phosphotransferase, pyruvate kinase and glucose-6-phosphate dehydrogenase in desalted extracts of the cells grown in the complete medium were slightly (after 24 hr of culture) or markedly higher (after 72 hr) than those in the extracts of cells grown in Pi-deficient medium. Pronounced increases in levels of ATP, PPi, and NADP+ were found only when the cells were transferred to the Pi-containing medium. The level of fructose-2,6-bisphosphate was significantly reduced in the cells grown in Pi-deficient medium. These results indicate that increased levels of phosphorylated compounds and of related enzymes induced by Pi may contribute to the enhancement of the catabolism of sugars. © 1990.