The Occurrence of Abscisic Acid and Abscisyl-β-d-Glucopyranoside in Developing and Mature Citrus Fruit as Determined by Enzyme Immunoassay

Abstract

The contents of (+)-cis-abscisic acid (ABA) and alkaline-hydrolyzable ABA-conjugate(s) were analyzed by means of enzyme immunoassay in partially purified extracts of developing and mature sweet orange fruit (Citrus sinensis [L.] Osbeck cv Washington navel). A relatively small increase in ABA was observed in the fruit exocarp during the natural color transition from green to orange. At the same time, the ABA-conjugate level increased approximately 12-fold in this tissue. The con-tents of ABA and ABA-conjugate equaled 15.0 ± 0.7 and 107.8 ± 2.1 nanomoles per gram fresh weight, respectively, in the exocarp at harvest. Other tissues also contained considerable quantities of these compounds. Whereas the highest ABA content was observed in the exocarp, the highest ABA-conjugate content was observed in the central vascular axis of the fruit and equaled 187.0 ± 103 nanomoles per gram fresh weight. The only immunoreactive conjugate found in significant quantity in ma-ture fruit was identified as abscisyl-,-D-glucopyranoside (ABA-GE) based on (a) immunological cross-reactivity, (b) thin layer