The role of the plasma membrane atpase in bentazone–sethoxydim antagonism

This study was carried out to gain more information concerning the mechanism by which bentazone reduces the herbicidal activity of sethoxydim. The possible roles of ATP and of the plasma membrane ATPase activity in the mechanism of antagonism were investigated. The first part of the study investigated the effect of exogenous ATP on the uptake of [14C]sethoxydim by wheat leaf segments. Uptake increased with ATP concentration, the magnitude of the increase depending on the time of day when the incubations were started. In the second part of the study plasma membranes from wheat leaves were isolated using two immiscible polymers, polyethylene glygol and dextran, and the activities of their ATPases were measured by monitoring the amount of inorganic phosphate produced. ATPase activity was lower in the presence of 500 μM bentazone and the magnitude of the decrease increased with the concentration of bentazone. Bentazone derivatives that reduce the uptake of sethoxydim but have no effect on photosynthesis also reduced ATPase activity. A mechanism is proposed by which bentazone could alter the uptake of sethoxydim by decreasing the activity of plasma membrane ATPases.