The Relation between the Synthesis of Inorganic Polyphosphate and Phosphate Uptake by Chlorella vulgaris

During a period of phosphate starvation, the phosphate contentof cells of Chlorella vulgaris which had been grown in phosphate-richsolution, decreased. The levels of most phosphate fractionsdeclined, especially those of inorganic polyphosphates, whichat first accounted for about 5 per cent of the total phosphateand virtually disappeared after 36 h starvation. On return toa phosphate medium, phosphate was taken up at a much fasterrate than before starvation, with a striking increase in acid-solublepolyphosphate. The stimulated phosphate uptake and polyphosphateincrease have been shown to be specific effects of phosphatestarvation, occurred only when excess phosphate was suppliedand required light or air for the provision of energy. Therewas relatively little change in the concentrations of otherphosphate fractions, including orthophosphate. Inorganic polyphosphatewas found to be synthesized solely from phosphate absorbed fromthe medium. It is argued that polyphosphate synthesis is a consequenceof the stimulation of phosphate uptake, induced by the starvationperiod.     

The Use of 6-MP to Investigate the Control of Glucose-6-Phosphate Dehydrogenase Levels in Cultured Artichoke Tissue

6-Methylpurine (6-MP) prevents the increase in glucose-6-phosphatedehydrogenase (G6PDH) activity which precedes the early periodof synchronous division in Jerusalem artichoke explants, evenwhen added less than 1 h before the increase occurs in non-inhibitedcultures. A study of amino-acid and uridine incorporation showsthat 6-MP specifically inhibits nucleoside incorporation overshort-term periods but that longer exposure causes inhibitionof aminoacid incorporation as well. The implication of thisobservation on the use of 6-MP and other supposed specific RNAinhibitors is discussed. Possible points of control of G6PDHsynthesis are considered.