Abscisic acid metabolism in Ceratocystis coerulescens

The fungus Ceratocystis coerulescens Bakshi (strain RWD 390) has been shown to produce the plant hormone, abscisic acid (ABA). The production of ABA in defined liquid medium during a culture period of 50 days was measured by gas‐liquid chromatography. A considerable accumulation of ABA occurred in the stationary phase. Maximum ABA contents were 3.5 ng ml−1 in culture media and 218 ng (g dry weight)−1 in mycelial extracts. The ABA‐metabolizing capability of the fungus was investigated. Dihydrophaseic acid, and phaseic acid, ABA metabolites in higher plants, were not present in cultures of Ceratocystis coerulescens. When [2‐14C]‐ABA was fed to the fungus, the formation of [2‐14C]‐2‐trans, 4‐trans‐ABA and a second metabolite, less polar than ABA, was observed. This suggests a different metabolic pathway of ABA in the fungus.