Differential response of plant cell membranes to some vinyl organophosphorus insecticides

The response of plant cell membranes to vinyl organophosphorus insecticides was studied by determining the release of intracellular materials as a measure of membrane permeability and the uptake of 1-¹⁴C]-α-aminoisobutyric acid as a measure of active transport. A pretreatment with chlorfenvinphos (2-chloro-1-(2,4-dichlorophenyl)-vinyl diethyl phosphate) at 0.4 mM or higher concentrations increased the leakage of cell contents from the tissues of pea, corn, and beet, but two other vinyl organophosphorus insecticides, tetrachlorvinphos (2-chloro-1-(2,4,5-trichlorophenyl)-vinyl diethyl phosphate) and phosphamidon (2-chloro-2-diethyl carbamoyl-1-methyl vinyl dimethyl phosphate), had no effect. Simultaneous addition of phospholipids, β-sitosterol, or Ca²⁺ inhibited in varying degrees the chlorfenvinphos-induced permeability, suggesting that the leakage of cell contents might be due to alteration in membrane structure.Chlorfenvinphos or tetrachlorvinphos at 0.1 mM or higher concentrations inhibited the uptake of α-aminoisobutyric acid. The degree of inhibition varied with different plant species. The inhibition was competitive and was not prevented by phospholipids. However, Ca²⁺ and other divalent cations were stimulatory to the uptake of α-aminoisobutyric acid, either in the presence or absence of chlorfenvinphos. Chlorfenvinphos also inhibited plant growth in tobacco callus and pea stem assays.From the differences in effective concentration, structural requirement, and interaction with phospholipids, it is suggested that chlorfenvinphos affected the membrane permeability and active transport by different mechanisms. These effects probably underlie its inhibitory action on plant growth.