Abstract
Summary ( 14 C)abscisic acid release from preloaded leaf slices of various plants was stimulated by hypertonic treatment. Wilting-induced efflux of ABA from the mesophyll and a transient increase of ( 14 C)ABA in the lower epidermis was also observed in preloaded leaf discs. The data indicate that water stress does not only affect ABA synthesis and metabolism, but also ABA distribution between symplast and apoplast and between various leaf tissues. External osmotic potentials (π o ) needed for a given ABA efflux were closely related to the osmotic potentials of the cell sap (π cs ) which was very different for various plants. The trigger for stress induced ABA efflux from the mesophyll appeared to be cell shrinkage rather than turgor changes.
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