Localization of abscisic acid in grape berry by immunohistochemical techniques

Abstract

In the grape berry, which accumulates abscisic acid (ABA) markedly during ripening, the localization of this hormone was investigated by instrumental analysis and immunohistochemistry using an indirect immunoperoxidase method. In the instrumental analysis the levels of ABA in the outer wall, inner wall and placenta from unripe berries were nearly the same, ranging between 50 to 80 ng/gfw. After veraison, ABA levels in these tissues increased and reached a peak at 11 weeks after full bloom. The lowest level of ABA was in the inner wall; it was intermediate in the outer wall, and highest in the placenta. Mouse antiserum raised against free (+) cis, trans abscisic acid was used in the first immunostaining step. Although positive immunoreactivity was detected on the sections, there were no visible differences in the immunoreactivity of the outer wall, inner wall and placenta. Phloem in both the peripheral and the central vascular bundles revealed high immunoreactivity in the ripe, but not in the unripe grape berries. In the ripe grape berry, the immunoreactivity of xylem in the peripheral and central vascular bundles was considerably lower than that of the phloem. This result suggests that the transport of abscisic acid from the leaves via the phloem contributes to its increase in the grape berry during ripening.