Distribution of ABA and IAA in asparagus

Asparagus spears had a extraordinary growth rate. The elucidation of a mechanism of the high growth ability of those may afford a clue for the improvement of cultivations in other products. Changes in the levels or spatial distribution of abscisic acid (ABA) and 2-trans-abscisic acid (t-ABA) were analyzed in different sections of spears, buds, rhizomes and roots of dark-grown asparagus (Asparagus officinalis L. cv. Mary Washington 500 W). As to spears, indole-acetic acid (IAA) was also analyzed. Spear tips maintained constant high levels of ABA during their elongation and there was a declining gradient from the apex toward the base. The growth rate showed a large gradient, declining from the zone of elongation to the butt region. As lateral buds started their growth, ABA concentration in lateral buds plus scale leaves associated with the tip region was the highest among all tested tissues, and ABA concentrations of all regions in spears increased compared to those before stage. In rhizomes, ABA concentration was higher in the younger regions where buds would sprout. The concentrations of the physiologically less active t-ABA in spears also showed a gradient, declining from the tip to the butt region in all parts, but was less in absolute amounts. The growing spears also had a declining gradient of IAA concentration, suggesting that IAA may promote a spear elongation. These results suggested that ABA and IAA may contribute to physiological effects in the vegetative organ of asparagus.