PLANT PHYSIOLOGY , Vol 105, Issue 2 607-610, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Incorporation of Label from 13C-, 2H-, and 15N-Labeled Methionine Molecules during the Biosynthesis of 2[prime]-Deoxymugineic Acid in Roots of Wheat
J. F. Ma and K. Nomoto
Suntory Institute for Bioorganic Research, Shimamoto-cho,Mishima-gun,Osaka,618, Japan
The biosynthetic pathway of 2[prime]-deoxymugineic acid, a key
phytosiderophore, was investigated by feeding 13C-, 2H-, and 15N-labeled
methionine, the first precursor, to the roots of hydroponically cultured
wheat (Triticum aestivum L. cv Minori). The incorporation of label from
each methionine species was observed during their conversion to
2[prime]-deoxymugineic acid, using 2H-, 15N-, and 13C-nuclear magnetic
resonance (NMR). L-[1-13C]Methionine (99% 13C) was efficiently
incorporated, resulting in 13C enrichment of the three carboxyl groups of
2[prime]-deoxymugineic acid. Use of D,L-[15N]methionine (95% 15N) resulted
in 15N enrichment of 2[prime]-deoxymugineic acid at the azetidine ring
nitrogen and the secondary amino nitrogen. When
D,L-[2,3,3,-2H3-S-methyl-2H3]methionine (98.2% 2H) was fed to the roots,
2H-NMR results indicated that only six deuterium atoms were incorporated,
and that the deuterium atom from the C-2 position of each methionine was
almost completely lost. [2,2,3,3-2H4]1-Aminocyclopropane-1-carboxylic acid
(98% 2H) was not incorporated into 2[prime]-deoxymugineic acid. These data
and our previous findings demonstrated that only the deuterium atom from
the C-2 position of L-methionine was lost, and that other atoms were
completely incorporated when three molecules of methionine were converted
to 2[prime]-deoxymugineic acid. These observations are consistent with the
conversion of L-methionine to azetidine-2-carboxylic acid, suggesting that
L-methionine is first converted to azetidine-2-carboxylic acid during
biosynthesis leading to 2[prime]-deoxymugineic acid. Based on these
results, a hypothetical pathway from L-methionine to 2[prime]-deoxymugineic
acid was postulated.
