In suspension cultures of Catharanthus roseus the cyanide‐resistant pathway is engaged in respiration by excess sugar in combination with phosphate or nitrogen starvation

Abstract

Suspension cultured cells of Catharanthus roseus were used to study the effects of excess sugar, and phosphate or nitrogen starvation on growth and respiration. Excess sugar resulted in a higher dry weight but the cell number was not significantly higher than in the controls. After inoculation in phosphate‐free medium almost no growth was observed, whereas in medium without nitrogen some growth still occurred, indicating that the medium contains more than enough nitrogen and only a limited amount of phosphate. The maintenance respiration in the nitrogen‐free medium was lower than in the control, probably as a result of a lower protein production. In phosphate‐free medium, however, the maintenance respiration was higher, because the cyanide‐resistant pathway was engaged and the P/O ratio was decreased. In Catharanthus roseus cells the cyanide‐resistant pathway is engaged upon phosphate or nitrogen starvation in combination with excess sugar, while excess sugar, as such, does not engage the cyanide‐resistant pathway. In the presence of excess sugar the rate of glycolysis is adenylate‐controlled. It is only in combination with mineral starvation that the rate of glycolysis does not match the capacity of the cytochrome pathway, resulting in an overflow via the alternative pathway. After combination of mineral starvation with a low sugar supply the rate of glycolysis is controlled by both the substrate supply and the adenylates, and the cyanide‐resistant pathway is not engaged.