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PLANT PHYSIOLOGY , Vol 102, Issue 2 373-378, Copyright © 1993 by American Society of Plant Biologists
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ENVIRONMENTAL AND STRESS PHYSIOLOGY |
Two Related Biosynthetic Pathways of Mugineic Acids in Gramineous Plants
J. F. Ma and K. Nomoto
Suntory Institute for Bioorganic Research, Shimamoto-cho, Mishima-gun, Osaka, 618, Japan
The biosynthesis of mugineic acids was studied by feeding 2H- or
13C-labeled compounds to water-cultured roots in several gramineous plants.
The fate of labeled compounds was monitored by using 2H- and 13C-nuclear
magnetic resonance. On investigating the proton changes during biosynthesis
by feeding D,L-[3,3,4,4-d4]-methionine (98.6% 2H), 2H-labeled
2[prime]-deoxymugineic, mugineic, and 3-epihydroxymugineic acids were
isolated from root washings of wheat (Triticum aestivum L. cv Minori),
barley (Hordeum vulgare L. cv Minorimugi), and beer barley (Hordeum vulgare
L. cv AM Nijo Tochigi), respectively. The 2H-nuclear magnetic resonance
study indicated that 12 deuteriums were incorporated into the labeled
2[prime]-deoxymugineic acid, suggesting that three molecules of
L-[3,3,4,4-d4]methionine were combined. In comparison, one of the
deuteriums at C-2[prime] position in the mugineic acid, and one each of the
deuteriums at C-2[prime] and C-3 positions in the 3-epihydroxymugineic
acid, were lost. However, all other deuteriums were incorporated in a
manner similar to that of the labeled 2[prime]-deoxymugineic acid. When
[1,4[prime],4"-13C3]2[prime]-deoxymugineic acid (20% 13C) was fed to oat
roots (Avena sativa L. cv Amuri II), avenic acid A, which was 13C enriched
at the corresponding positions, was obtained. These results revealed that
L-methionine was the precursor for all these mugineic acids and that
cleavage of the azetidine ring or hydroxylation of the
2[prime]-deoxymugineic acid produced two related biosynthetic pathways in
different gramineous plant species: L-methionine ->
2[prime]-deoxymugineic acid -> avenic acid A in oat; and L-methionine
-> 2[prime]-deoxymugineic acid -> mugineic acid ->
3-epihydroxymugineic acid in barley and beer barley.
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