J. Chamarro et al., Metabolism of indole-3-acetic acid by orange (Citrus sinensis) flavedo tissue during fruit development, PHYTOCHEM, 57(2), 2001, pp. 179-187
[5-H-3, 1'-C-14, C-13(6), C-12] Indole-3-acetic acid (IAA), was applied to
the flavedo (epicarp) of intact orange fruits at different stages of develo
pment, after incubation in the dark, at 25 degreesC, the tissue was extract
ed with MeOH and the partially purified extracts were analyzed by reversed
phase HPLC-RC. Six major metabolite peaks were detected and subsequently an
alyzed by combined HPLC-frit-FaB-MS. The metabolite peak 6 contained oxindo
le-3-acetic acid (OxIAA), indole-3-acetyl-N-aspartic acid (IAAsp) and also
indole-3-acetyl-N-glutamic acid (IAGlu). The nature of metabolite 5 remains
unknown. Metabolites 3 and 4 were diastereomers of oxindole-3-acetyl-N-asp
artic acid (OxIAAsp). Metabolite 2 was identified as dioxindole-3-acetic ac
id and metabolite 1 as a DiOx-IAA linked in position three to a hexose, whi
ch is suggested to be 3-(-O-beta -glucosyl) dioxindole-3-acetic acid (DiOxI
AGlc). Identification work as well as feeding experiments with the [5-3H]IA
A labeled metabolites suggest that IAA is metabolized in flavedo tissue mai
nly through two pathways, namely IAA-OxIAA-DiOxIAA-DiOxIAGlc and IAA-IAAsp-
OxIAAsp. The flavedo of citrus fruit has a high capacity for IAA catabolism
until the beginning of fruit senescence, with the major route having DiOxI
AGlc as end product. This capacity is operative even at high IAA concentrat
ions and is accelerated by pretreatment with the synthetic auxins 2,4-D, NA
A and the gibberellin GA(3). (C) 2001 Elsevier Science Ltd. All rights rese
rved.