ABSTRACT
The history of the discovery of abscisic acid is suggestive in considering the process of developmental research of biologically active substances. The research on abscisic acid was started by several groups whose work was not apparently related initially. After many turns and twists, they finally converged on abscisic acid, which was found to be a plant hormone with important roles in plant physiology. ABA has been detected in various higher plants including Spermatophyta and Pteridophyta. It is likely that there is no vascular plant which does not contain ABA. The species of ABA-producing fungi known so far are restricted to phytopathogenic ones, thus there is a possibility that the ABA biosynthesis gene of plants might have been transferred into fungi in a process of co-evolution between host plants and parasites, rather than the ABA-producing fungi being the evolutionary origin of higher plants.
