Abstract
Growth of suspension-cultured Catharanthus roseus cells ceased during phosphate starvation, but the cells grew again upon addition of Pi even after long-term starvation. The metabolic fate of [33P]Pi was studied in Pi-starved cells. Immediately after administration, the most heavily labelled organic compounds are nucleotides, followed by sugar phosphates. The RNA, protein and free nucleotide content decreased gradually during Pi-starvation; however, these compounds, especially nucleoside triphosphates and UDP-glucose, increased markedly after addition of Pi. The transcript level of phosphate transporter and the activities of acid phosphatase, 5'- ,3'- nucleotidase and adenosine nucleosidase were all reduced by the addition of Pi. In contrast, the activities of adenine phosphoribosyltransferase, nicotinate phosphoribosyltransferase and nicotinamidase were markedly increased in the Pi-fed cells. Little or no increase was observed in adenosine kinase. In the light of these results we discuss the possible involvement of net nucleotide synthesis in the initial metabolic events of recovery from Pi-deficiency.
