An investigation of herbicide interaction with the H+-ATPase activity of plant plasma membranes

This study has investigated the activity of several herbicide classes at the plant plasma membrane. Two‐phase partitioning was used to prepare highly purified plasma membrane vesicles from the monocotyledon weed black‐grass (Alopecurus myosuroides Huds.) and the dicotyledon crop sugar beet (Beta vulgaris L. cv. Celt). The purity of the plasma membrane H+‐ATPase activity was characterised with respect to inhibitors, pH and substrate specificity. In both species, contamination of the plasma membrane by tonoplast fragments was largely eliminated and chlorophyll was absent. In addition, the plasma membrane H+‐ATPase from black‐grass and sugar beet exhibited high vanadate sensitivity and a sharp pH profile around 6·5. Subsequently, H+‐ATPase activity was assayed in the presence (100 μM) and absence of four graminicide classes and auxin‐type herbicides. Graminicides, including the aryloxyphenoxypropionate diclofop‐methyl and the thiocarbamate triallate, inhibited H+‐ATPase activity by 50–80% in both species. However, other graminicides, including the cyclohexanediones and the chloroacetamide alachlor, had no affect. Similarly, auxin‐type herbicides such as 2,4‐D and MCPA did not inhibit H+‐ATPase activity. Results are discussed in relation to the proposed mode of action of these herbicides. © 1998 SCI