COMPARATIVE STUDY OF THE TISSUE-SPECIFIC DISTRIBUTION OF ABA FROM ARACHIS HYPOGAEA L. AND EXPRESSION OF THE 9-CIS EPOXYCAROTENOID DIOXYGENASE 1 (AHNCED1) DURING PLANT DEVELOPMENT

The oxidative cleavage of cis-epoxycarotenoids catalyzed by 9-cis-epoxycarotenoid dioxygenase (NCED) is considered to be the rate-limiting step in abscisic acid (ABA) biosynthesis. In this study, the tissue-specific distribution of ABA in peanut plants during development, and the relationship and influence between tissue-specific distribution of ABA and tissue-specific expression of AhNCED1 were studied by immunoenzyme localization. At the four-leaf stage, ABA and AhNCED1 immunohistochemical specific staining was detected in the root vascular parenchyma. During the blooming stage, there was no ABA and AhNCED1 immunohistochemical specific staining in any of the analyzed organs (leaf stem, including root). However, ABA immunohistochemical specific staining was detected in the leaf vascular parenchyma during the fruiting stage. The organ-specific pattern of AhNCED1 mRNA and protein expression under water stress was consistent with that of ABA accumulation. The results suggest that ABA biosynthesis in peanut plants occurs predominantly in the vascular parenchyma cells. In peanut plants, initial ABA biosynthesis occurs in different organs during the different developmental stages: the root is the initial organ of ABA biosynthesis at the four-leaf stage, whereas leaves play this role at the fruiting stages.