ABSTRACT
The physiological activity of selected surfactants commonly used in agriculture and/or representing selected chemistries was determined using beet root tissue (Beta vulgaris L.) as a model system. Biological activity was assessed by measuring simultaneously the effect of the surfactant on the induction of ethylene evolution and on membrane integrity. Tissue discs were incubated in appropriate test solutions at pH 7 for 3 h at 30°C in the dark. Ethylene was determined by gas chromatographic analysis of headspace samples, and membrane integrity was assessed by spectrophotometrically measuring betacyanin efflux into the incubation medium. Surfactants either promoted, had no effect on, or suppressed ethylene evolution, while they either increased or had no effect on membrane permeability. Responses of both systems were related to surfactant chemistry and concentration. Of 29 surfactants evaluated, 18 enhanced both ethylene evolution and betacyanin efflux, while only 5 enhanced ethylene production without affecting membrane integrity. Five enhanced betacyanin efflux but depressed ethylene evolution. One had no significant effect on either parameter. In general, polyoxyethylene derivatives of octylphenol, nonylphenol, and linear alcohols (C9-11 C12–15 hydrophobe) decreased in biological activity with increasing oxyethylene chain length. For most surfactants, the minimum effective concentrations for induction of ethylene evolution and pigment efflux were 0.01 and 0.05%, respectively. The relationships between surfactant chemistry and ethylene evolution and membrane integrity are discussed.
