PLANT PHYSIOLOGY , Vol 106, Issue 1 321-328, Copyright © 1994 by American Society of Plant Biologists
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METABOLISM AND ENZYMOLOGY |
Herbicidal Activity of an Isopropylmalate Dehydrogenase Inhibitor
V. A. Wittenbach, P. W. Teaney, W. S. Hanna, D. R. Rayner and J. V. Schloss
DuPont Agricultural Products, Stine-Haskell Research Center, Newark, Delaware 19714
Isopropylmalate dehydrogenase (IPMDH) is the third enzyme specific to
leucine biosynthesis. It catalyzes the oxidative decarboxylation of
3-isopropylmalate (3-IPM) to 2-ketoisocaproic acid. The partially purified
enzyme from pea (Pisum sativum L.) shows a broad pH optimum of 7.8 to 9.1
and has Km values for 3-IPM and NAD of 18 and 40 [mu]M, respectively.
O-Isobutenyl oxalylhydroxamate (O-IbOHA) has been discovered to be an
excellent inhibitor of the pea IPMDH, with an apparent inhibitor constant
of 5 nM. As an herbicide, O-IbOHA showed only moderate activity on a
variety of broadleaf and grass species. We characterized the herbicidal
activity of O-IbOHA on corn (Zea mays L.), a sensitive species; giant
foxtail (Setaria faberi) and morning glory (Ipomoea purpurea [L.] Roth),
moderately tolerant species; and soybean [Glycine max L. Merr.), a tolerant
species. Differences in tolerance among the species were not due to
differences in the sensitivity of IPMDH. Studies with [14C]O-IbOHA
suggested that uptake and translocation were not major limitations for
herbicidal activity, nor were they determinants of tolerance. Moreover,
metabolism could not account for the difference in tolerance of corn,
foxtail, and morning glory, although it might account for the tolerance of
soybean. Herbicidal activity on all four species was correlated with the
accumulation of 3-IPM in the plants.
