Effect of Inorganic Phosphate on the Biosynthesis of Purine and Pyrimidine Nucleotides in Suspension-Cultured Cells of Catharanthus roseus

The levels of purine and pyrimidine nucleotides in suspensioncultures of Catharanthus roseus were determined 24 h after stationary-phasecells were transferred to fresh complete (‘+Pi’)or phosphate-deficient (‘–Pi’) Murashige-Skoogmedium. The levels of ATP, GTP, UTP and CTP were from approx.3 to 5-fold greater in the cells grown in ‘+Pi’medium than in the cells grown in ‘–Pi’ medium.The levels of almost all other nucleotides were slightly higherin the cells in ‘+Pi’ medium. The rates of de novoand salvage biosynthesis of purine and pyrimidine nucleotideswere estimated from the rates of incorporation of radioactivityfrom ¹⁴C]formate, 2–¹⁴C]glycine, NaH¹⁴CO₃, 6–¹⁴C]orotate,8–¹⁴C]adenine, 8–¹⁴C]adenosine, 2–¹⁴C]uraciland 2–¹⁴C]uridine. The results indicated that the activityof both the de novo and the salvage pathway was higher in thecells in ‘+Pi’ medium than in the cells in ‘–Pi’medium. The rate of degradation estimated from the rate of releaseof ¹⁴CO₂ from labelled purines and pyrimidines indicated thatdegradation of uridine was significantly reduced in the cellsin ‘+Pi’ medium, but no significant difference wasfound in the degradation of adenine, adenosine and uracil. Thepossible role of Pi in the control of the biosynthesis of nucleotidesand in the degradation of uridine is discussed. Catharanthus roseus, Madagascar periwinkle, suspension culture, inorganic phosphate, nucleotides, purines, pyrimidines, biosynthesis, degradation