PLANT PHYSIOLOGY , Vol 101, Issue 1 313-320, Copyright © 1993 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Conjugation of Indole-3-Acetic Acid (IAA) in Wild-Type and IAA-Overprodcing Transgenic Tobacco Plants, and Identification of the Main Conjugates by Frit-Fast Atom Bombardment Liquid Chromatography-Mass Spectrometry
F. Sitbon, A. Ostin, B. Sundberg, O. Olsson and G. Sandberg
Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, S-901 83 Umea, Sweden
Transgenic plants overproducing indole-3-acetic acid (IAA) from expression
of the Agrobacterium tumefaciens T-DNA IAA biosynthesis genes were used to
study the conjugation of IAA. At the 11-node stage, free IAA, as well as
ester- and amide-conjugated IAA, was analyzed in wild-type tobacco SR1 and
in transgenic plants denoted 35S-iaaM/iaaH (line C) and 35S-iaaM x 35S-iaaH
(line X). The transgenic plants contained increased levels of both free and
conjugated IAA, and the main increase in IAA conjugates occurred in amide
conjugates. Two amide conjugates were identified by fritfast atom
bombardment liquid chromatography-mass spectrometry as
indole-3-acetylaspartic acid (IAAsp) and indole-3-acetylglutamic acid
(IAGlu), and one ester conjugate was identified as indole-3-acetylglucose.
IAAsp and IAGlu were also identified as endogenous substances in wild-type
plants. In wild-type plants, the percent of total IAA in the free form was
significantly higher in young leaves (73 [plus or minus] 7%, SD) than in
old leaves (36 [plus or minus] 8%), whereas there was no difference between
young (73 [plus or minus] 8%) and old internodes (70 [plus or minus] 9%).
In IAA-overproducing transformants, both free and conjugated IAA levels
were increased, but the percent free IAA was maintained constant (57 [plus
or minus] 10%) for both leaves and internodes, independent of the total IAA
level or tissue age. These results suggest that synthesis or transport of
IAA conjugates is regulated in the vegetative wild-type plant, and that
different organs possess a unique balance between free and conjugated IAA.
The IAA-overproducing plant, however, acquires a lower proportion of free
IAA in the stem and younger leaves, presumably determined by a higher
conjugation in those tissues compared with wild type.
