Abscisic Acid-related changes in composition and physical state of membranes in bean leaves.

Leaf discs of bean, maize, and wheat were incubated in the presence of either 2-(14)C mevalonic acid or methyl-(14)C choline chloride and varying concentrations of abscisic acid. Abscisic acid inhibited, dependent on concentration, the incorporation of mevalonate into free sterols and stimulated the incorporation of choline chloride into phosphatidylcholine. As a result the dpm ratio of free sterols to phosphatidylcholine decreased. Untreated bean leaf membranes exhibited phase separation temperatures at around 17 and 9°C using the TEMPO in vivo spin labelling technique. Both the upper and lower phase separation temperatures were shifted to lower temperatures in chill, or water stressed plants. Administration of abscisic acid brought about corre-sponding changes in phase behaviour of leaf membranes. It is suggested that beneficial effect of the hormone on chill tolerance of plants manifests itself, at least partially, thorough the modification of the physical state of membranes.