Uptake of DTP, the herbicidal entity of pyrazolate, by corn root protoplasts
1995
Kasai, F. | Bayer, D.E.
The uptake of DTP [4-(2,4-dichlorobenzoyl)-1, 3-dimethyl-5-hydroxypyrazole], the herbicidal entity of pyrazolate, by corn (Zea mays L. cv. Pioneer 3377) root protoplasts increased as the external pH (pH degrees) decreased. The ratio of the DTP concentration inside to outside the protoplasts (c(i)/c(o)) reached ca. 0.4, 2.0, 9.0, and 35 to 40 at pH degrees 7.5, 6.5, 5.5, and 4.5, respectively, within 75 min of incubation. These data quantitatively agreed with the theoretical values expected from the weak acid hypothesis. Five metabolic inhibitors with different types of action inhibited DTP accumulation by the protoplasts and the inhibition was closely correlated with the reduction in intracellular pH regardless of the type of action of the inhibitors. These results suggest that a predominant component of DTP absorption and retention is the diffusion of undissociated DTP molecules, which is indirectly driven by the pH gradient across the plasmalemma. The calculation based on the diffusion equilibrium predicted that if a typical plant cell is exposed to paddy water (pH 5.7) containing 1 ppm DTP, the DTP concentrations accumulated in the cytoplasm and the vacuole would be 75 and 0.6 ppm, respectively. This suggests that the absorbed DTP would be highly accumulated in the cytoplasm thereby effectively performing its herbicidal activity.
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