The Short-Term Effects of Inorganic Phosphate on the Levels of Metabolites in Suspension-Cultured Catharanthus roseus Cells*

In order to analyze the effects of inorganic phosphate (Pi) on the energy metabolism of suspen­ sion-cultured cells o f Catharanthus roseus, short-term changes in levels of glycolytic m etabolites were monitored after the addition o f 1.25 mM Pi to cultures of cells previously cultured in a Pi-free M urashige-Skoog medium for 24 h. The levels of all phosphorylated intermediates o f glycolysis exam ined were found to increase after addition of Pi. The most striking increases were observed in levels of glucose-6-phosphate and fructose-6-phosphate which rose to approximately 8 (after 30 min) and 15 times (after 120 min) their initial values. The levels of ATP and pyrophosphate doubled during the first 30 min of incubation. In contrast, the level of pyruvate decreased signifi­ cantly during the initial 30 min and then began to increase again for the next 90 min. The short­ term effects of Pi on the rates of synthesis o f proteins and RNA were estimated from the rates of incorporation o f 14C-labelled amino acids and uridine into the macromolecules. No appreciable stimulation of the synthesis of proteins and R N A was induced by Pi within 120 min after the addition of Pi. Possible mechanisms are discussed that may be involved in the changes in m etabo­ lism initiated by the addition of Pi to the cultures.