Regulation of Abscisic Acid Formation in Mycosphaerella (Cercospora) rosicola by Phosphate

Abstract

The regulation by phosphate of abscisic acid (ABA) production by M. (Cercospora) rosicola was examined in defined-media, submerged shake cultures. Phosphate concentrations < 0.5 mM were suboptimal for growth and caused ABA synthesis to begin earlier than at 0.5 mM, the optimal concentration for maximal yield of ABA. Higher concentrations of phosphate gave progressively greater suppression of ABA formation while dry weight yield was essentially constant from 0.5-10 mM. Addition of 5 mM phosphate to phosphate-limited cultures at various times showed that there was a critical period during the first 3-5 days of incubation during log growth and before ABA synthesis had begun when the fungus was sensitive to phosphate suppression.