Transport and Compartmentation of Abscisic Acid in Roots ofHordeum distichonunder Osmotic Stress

Using modified compartmental analysis the unidirectional fluxes of abscisic acid (ABA) and their cytoplasmic and vacuolar contents in 3H-ABA preloaded barley root segments (Hordeum distichon cv. Aura) have been studied. When root segments were stressed osmotically with sorbitol (osmotic potential of the media π0 = 0.2 MPa) cytoplasmic and vacuolar contents of ABA were enhanced. Under increased stress cytoplasmic and vacuolar contents were much lower than in the unstressed controls. ABA fluxes were very sensitive to osmotic stress and ABA transport from the cytoplasm of the xylem parenchyma to the xylem vessels (φcx) was rapidly inhibited. The cultivar Aura has higher cytoplasmic and vacuolar ABA contents than the barley cultivar Kocherperle. This correlates well with the higher stress tolerance of the Aura cultivar.