A secondary mode of action of the herbicide lenacil: Modification of K+ permeability of Acer pseudoplatanus cells

Abstract The action of lenacil on plasmalemma permeability to K + , transmembrane electric potential difference (PD) calculated from the tetraphenylphosphonium distribution, proton extrusion and intracellular pH of Acer pseudoplatanus cells calculated from the 5,5-dimethyloxazolidine,4-dione distribution, was studied and compared with the action of fusicoccin (FC) and diethylstilbestrol (DES). The three compounds temporarily stimulated the rate of 86 Rb + uptake with a half-maximum effect at 5.0 μM for 3-cyclohexyl-6, 7-dihdro-1H-cyclopentapyrimidine-2,4(3H,5H)-dione (lenacil). Lenacil and FC had no action on transmembrane electric potential difference, whereas DES decreased it. Lenacil inhibited proton extrusion induced by FC similarity to DES. Only DES lowered internal pH (pH i ). The kinetics of K + absorption suggested that the permeability of plasmalemma was affected by lenacil. Since half-maximum stimulation of K + absorption was reached at roughly 6 times the concentration required to 50% inhibit photosynthesis, this mode of action, although of secondary importance, probably plays a role in the phytotoxic effect of lenacil.