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Mechanisms of diclofop methyl uptake in oat protoplasts (Avena sativa ’Cascade’) Tritter, Susan


Isolated oat protoplasts ( Avena sativa L. 'Cascade') were used to compare the uptake of the herbicide diclofop methyl (methyl 2-(4-(2,4-diehlorophenoxy)phenoxy)propanoate) and the acid form diclofop (2-(4-(2,4-dichlorophenoxy)phenoxy) propionic acid and to study herbicide uptake as a basis for the 2,4-D-diclofop methyl antagonism. Diclofop methyl was rapidly taken up by protoplasts (≤ 5 seconds) to a constant level which did not change significantly with incubation times up to 1.0 hour. Forty percent of added 14C-diclofop methyl was taken up within 5.0 seconds while diclofop uptake was limited over the same time period. Diclofop methyl uptake was linear with herbicide concentration in the uptake solution up to 50 μM. There was no significant difference between uptake by burst or intact protoplasts preparations. Large accumulations of 14C-diclofop methyl were found in the membrane fractions of the protoplasts. Diclofop methyl uptake appeared to be a passive, non-mediated process in which the herbicide was partitioned into the lipid phase of the protoplast membrane. Diclofop methyl was converted to the acid form in the treatment solution by hydrolase enzymes apparently associated with the external surface of the protoplast plasma membrane. 2,4-D did not affect diclofop methyl or diclofop uptake at concentrations from 10 μM to 2.0 mM nor was the conversion of diclofop methyl to diclofop affected by 2,4-D except at high non-physiological concentrations. Diclofop methyl and diclofop did not adversely affect membrane permeability of the protoplasts at the herbicide concentrations used in these experiments. Protoplast preparations proved to be a useful and simple system to study the uptake and metabolism of herbicides in plants.

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