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Diclofop-methyl increases the proton permeability of isolated oat-root tonoplast
1Department of Agronomy, University of Wisconsin-Madison, Madison, Wisconsin 53706.
Abstract:
Diclofop-methyl (methyl ester of 2-[4-(2',4'-dichlorophenoxy)phenoxy]propionate; 100 micromolar) and diclofop (100 micromolar) inhibited both ATP- and PPi-dependent formation of H(+) gradients by tonoplast vesicles isolated from oat (Avena sativa L., cv Dal) roots. Diclofop-methyl (1 micromolar) significantly reduced the steady-state H(+) gradient generated in the presence of ATP. The ester (diclofop-methyl) was more inhibitory than the free acid (diclofop) at pH 7.4, but this relative activity was reversed at pH 5.7. Neither compound affected the rate of ATP or PPi hydrolysis by the proton-pumping enzymes. Diclofop-methyl (50, 100 micromolar), but not diclofop (100 micromolar), accelerated the decay of nonmetabolic H(+) gradients established across vesicle membranes. Diclofop-methyl (100 micromolar) did not collapse K(+) gradients across vesicle membranes. Both the (+)- and (-)-enantiomers of diclofop-methyl dissipated nonmetabolic H(+) gradients established across vesicle membranes. Diclofop-methyl, but not diclofop (each 100 micromolar), accelerated the decay of H(+) gradients imposed across liposomal membranes. These results show that diclofop-methyl causes a specific increase in the H(+) permeability of tonoplast.
Insights
Diclofop-methyl and diclofop inhibit proton gradient formation in oat root tonoplast vesicles. Diclofop-methyl specifically increases tonoplast H(+) permeability, affecting proton transport.
Area of Science:
- Plant Physiology
- Biochemistry
- Molecular Biology
Background:
- Tonoplast vesicles are crucial for maintaining cellular pH and ion homeostasis in plants.
- Proton pumps in the tonoplast regulate nutrient uptake and waste sequestration.
- Understanding herbicide interactions with plant membranes is vital for agricultural science.
Purpose of the Study:
- To investigate the effects of diclofop-methyl and diclofop on proton (H+) gradient formation in oat root tonoplast vesicles.
- To determine the specific mechanisms by which these herbicides impact tonoplast function.
- To elucidate the role of diclofop-methyl in altering membrane permeability.
Main Methods:
- Isolation of tonoplast vesicles from oat (Avena sativa L.) roots.
- Measurement of ATP- and pyrophosphate (PPi)-dependent H+ gradient formation.
- Assay of H+ gradient decay and K+ gradient stability.
- Investigation of herbicide effects at different pH values and on liposomal membranes.
Main Results:
- Both diclofop-methyl and diclofop inhibited H+ gradient formation, with diclofop-methyl being more potent at pH 7.4.
- Diclofop-methyl accelerated the decay of nonmetabolic H+ gradients, indicating increased membrane permeability to protons.
- Neither herbicide affected ATP or PPi hydrolysis, suggesting a direct impact on membrane transport rather than enzyme activity.
- Both enantiomers of diclofop-methyl dissipated H+ gradients, and diclofop-methyl affected liposomal membranes.
Conclusions:
- Diclofop-methyl specifically increases the H+ permeability of the tonoplast in oat roots.
- The herbicide's action is distinct from its effect on proton-pumping enzymes.
- These findings provide insight into the phytotoxic mechanisms of diclofop-methyl at the membrane level.
