Possible role of adenylates in the engagement of the cyanideresistant pathway in nutrient‐starved Catharanthus roseus Cells

In Cathuranthus roseus (L.) G. Don cells the cyanide‐resistant pathway is engaged after phosphate or nitrogen starvation. Re‐addition of these nutrients disengaged it again. Re‐addition of phosphate leads to a transient disengagement which becomes only permanent after a second addition of phosphate. Disengagement after re‐addition of nitrogen is slow: it takes 9 days before the activity has disappeared. In this system the mechanism of engagement of the cyanide‐resistant pathway was studied. Addition of phosphate to phosphate‐starved cells induced cell division within 24 h. The disengagement of the cyanide‐resistant pathway was probably only an indirect effect of phosphate because the cellular P, content, which increased rapidly after addition, was low again before the cyanide‐resistant pathway was disengaged. A better correlation was observed between high ADP and adenylate content of the cells and disengagement of the cyanide‐resistant pathway. In addition it appeared that the engagement of the cyanide‐resistant pathway was not the result of a limited carrier capacity of the cytochrome pathway. It is tentatively concluded that the engagement of the cyanide‐resistant pathway in phosphate‐starved cells was the result of a limited adenylate content. After nitrogen addition to N‐starved cells, it took 5 days until the first growth occurred. Before the cyanide‐resistant pathway was disengaged, its activity increased with the increased respiration rate which preceded growth. Within 72 h a higher ADP content was observed, which was still high after 10 days. The stimulation of the cytochrome pathway by uncoupler was small and more or less the same with and without added nitrogen, as long as the cyanide‐resistant pathway was engaged. After disengagement the stimulation by uncoupler was significantly larger. It is suggested that the engagement during N‐starvation was the result of a limited carrier capacity of the cytochrome pathway. Stimulation of the metabolism by re‐addition of phosphate, nitrogen or sucrose resulted in a rapid increase in the levels of uracil nucleotides and uridine diphosphoglucose (UDPG) which are involved in sucrose metabolism.