PLANT PHYSIOLOGY , Vol 102, Issue 4 1319-1324, Copyright © 1993 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
An in Vitro System of Indole-3-Acetic Acid Formation from Tryptophan in Maize (Zea mays) Coleoptile Extracts
T. Koshiba and H. Matsuyama
Department of Biology (T.K.) and Department of Chemistry (H.M.), Tokyo Metropolitan University, Hachioji-shi, Tokyo 192-03, Japan
The formation of a product from tryptophan that had the same retention time
as that of authentic indole-3-acetic acid (IAA) on high performance liquid
chromatography was detected in crude extracts of maize (Zea mays)
coleoptiles. The product was identified as IAA by mass spectrometry. The
IAA-forming activity was co-purified with an indole-3-acetaldehyde (IAAld)
oxidase activity by chromatography on hydrophobic and gel filtration
(GPC-100) columns. During purification, the IAA-forming activity, rather
than that of IAAld oxidase, decreased; but when hemoprotein obtained from
the same tissue was added, activity recovered to the same level as that of
IAAld oxidase. The promotive activity of the hemoprotein was confirmed by
the result that the activity coincided with amounts of the hemoprotein
after GPC-100 column chromatography. The hemoprotein was characterized and
identified as a cytosolic ascorbate peroxidase (T. Koshiba [1993] Plant
Cell Physiol [in press]). The reaction of the IAA-forming activity was
apparently one step from tryptophan. The activity was inhibited by
2-mercaptoethanol. The optimum temperature for the IAA-forming system as
well as for the IAAld oxidase was 50 to 60[deg]C, and the acitivity at
30[deg]C was one-third to one-half of that at 60[deg]C. The system did not
discriminate the L- and D-enantiomers of tryptophan.
