Distribution of ABA and IAA within a Developing Valencia Orange Fruit and Its Parts

Abstract

Various parts of developing Valencia orange fruits were analyzed for abscisic acid (ABA) and indole-3-acetic acid (IAA) by gas chromatography-electron capture detector and -mass spectrometry-selective ion monitoring with ³H-ABA and [¹³C₆] IAA as internal standards. The flesh and seed weight increased rapidly, while the albedo and flavedo weight increased gradually. The seed had a large peak of ABA concentrations (21 nmol•g^-1 fresh weight) 150 days after full bloom (DAB), while the flesh had a small peak (5 nmol•g^-1 fresh weight). IAA concentration in the seed decreased till 150 DAB but remained higher than other parts. In the central vasuclar axis, the IAA concentration reached a peak on 119 DAB. The level remained higher than those of the flesh, albedo and flavedo. The albedo and falvedo had an equally low level of IAA. We speculate from the analyses of the different fruit parts that 1) the ABA in the seed and IAA in the central vascular axis play a role in the accumulation of assimilates; and 2) the difference in ABA concentrations between the pulp and the peel indicates that no cross transfer occurs between these two tissues.