Biosynthesis of Abscisic Acid under Osmotic Stress: Studies Based on a Dual Labelling Technique

Sterile liquid suspension cultures from grape pericarp tissue incorporate label from mevalonic acid into abscisic acid (ABA), some of which is subsequently released into the surrounding medium. The addition of mannitol to the culture medium caused plasmolysis of individual cells and increased ABA generation and release. Levels in the medium increased up to 30 fold over a period of 8 h in the presence of mannitol (720 milliosmol). A dual labelling technique using 14C and 3H mevalonic acid was developed to distinguish between labelled compounds produced by turgid tissue and those specifically associated with the substantial increase in ABA synthesis following mannitol treatment.