PLANT PHYSIOLOGY , Vol 109, Issue 1 213-219, Copyright © 1995 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Specific Binding of a Dichloroacetamide Herbicide Safener in Maize at a Site That Also Binds Thiocarbamate and Chloroacetanilide Herbicides
J. D. Walton and J. E. Casida
Environmental Chemistry and Toxicology Laboratory, Department of Environmental Science, Policy, and Management, University of California, Berkeley, California 94720-3112
Dichloroacetamide safeners such as N,N-diallyl-2,2-dichloroacetamide and
(R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine protect maize (Zea
mays) against injury from thiocarbamate and chloroacetanilide herbicides.
Binding activity of tritium-labeled
(R,S)-3-dichloroacetyl-2,2,5-trimethyl-1,3-oxazolidine (15 Ci/ mmol;
referred to as [3H]Saf) was characterized in extracts of etiolated maize
seedlings. The binding is saturable, involves a single class of binding
sites (Kd 0.12 [mu]M; maximal binding in coleoptiles 0.53 nmol/g fresh
weight, equivalent to 55 pmol/mg protein), and is sensitive to boiling and
protease treatment. Binding in etiolated maize seedlings is highest in the
coleoptile and lowest in the leaves. Binding of [3H]Saf also occurs in
etiolated sorghum (Sorghum bi-color) shoots but not several other cereals.
There is a good correlation between known safener effectiveness and the
concentration that inhibits [3H]Saf binding half-maximally among 21
dichloroacetamides and related compounds. N,N-Diallyl-2,2-dichloroacetamide
had the lowest inhibitor concentration that reduces specific binding by 50%
(IC50), 0.01 [mu]M. [3H]Saf binding is inhibited by 4 chloroacetanilide
herbicides with IC50 values of 0.07 to 0.48 [mu]M and by 12 thiocarbamate
herbicides and analogs with IC50 values of 0.06 to 2.3 [mu]M. The
inhibition of [3H]Saf binding by alachlor and S-ethyl dipropylthiocarbamate
is competitive.
