| Abstract: | ATPase activity was examined in plasma membrane (PM) fractionsprepared from mecoprop-resistant and -susceptible biotypes ofStellaria media L. (chickweed). Treatment with the herbicidecaused an 18% increase in ATP hydrolysis, but this was not significantlydifferent from control plants and was similar for both biotypes.However, there was an overall significant biotype effect, herbicide-resistantplants having greater enzyme activity than susceptible ones.Proton-pumping was readily demonstrated in PM fractions obtainedfrom both biotypes using the fluorescent probe amino-chloro-methoxyacridine(ACMA), indicating a relatively large proportion of 'inside-out'vesicles. Proton-pumping was significantly greater in PM preparationsobtained from the resistant compared with susceptible plants.The differences in ATPase activity between the two biotypescould not be attributed to differences in the main sterol orphospholipid components of the PM. There were no effects ofthe herbicide on ATP hydrolysis in vitro, but proton-pumpingwas affected in a herbicide concentration-dependent manner.At 1·0 mol m mecoprop caused an increase in the rateof proton-pumping, whereas at 10 and 100 mol m–6, an inhibitionin this rate was observed. Both biotypes behaved similarly,irrespective of mecoprop concentration. These data indicatethat mecoprop resistance in chickweed is unlikely to be dueto a direct effect of the herbicide on PM H+-ATPase activity. Key words: Stellaria media, mecoprop, ATPase, plasma membrane, herbicide resistance |
