SPATIAL-DISTRIBUTION OF ABSCISIC-ACID AND 2-TRANS-ABSCISIC ACID IN SPEARS, BUDS, RHIZOMES AND ROOTS OF ASPARAGUS (ASPARAGUS-OFFICINALIS L)

Changes in the levels and spatial distribution of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) were determined in different sections of spears, buds, rhizomes and roots of dark-grown asparagus (Asparagus officinalis L. cultivar 'Mary Washington 500 W'). In both buds and rhizomes, ABA level was higher in the younger regions where buds would sprout, while in the growing spears, there was a declining gradient from the morphological apex towards the base. Spear tips were characterized by constant high levels of ABA during their elongation. The growth rate was low in the tip region, and showed a large gradient, declining from the zone of elongation (located 15-35 mm from the tip) to the butt region. Once lateral buds began their growth, the content of ABA in lateral buds plus scale leaves associated with the tip region, was the highest among all tested tissues. The levels of the physiologically less active t-ABA, on a fresh weight basis, showed a gradient, declining from the tip to the butt region in all parts, but was less in absolute amounts. These results support the hypothesis that ABA is involved in mobilizing carbohydrate reserves for spear growth.