The effect of ionic surface-active agents on macroconidial plasma membrane of Fusarium sulphureum

A method was developed for direct assessment of changes in cytoplasmic volume and permeability of plasma membranes of intact cells to divalent cations. This technique, which ultilized an amphipathic spin label partitioning between intracellular aqueous and hydrophobic environments, allowed estimates of the proportion of cells in a homogenous population sustaining membrane damage associated with Ni+2 and water permeability and the rate at which such damage was induced. Several specific effects of cationic and anionic surfactants on the macroconidial plasma membranes of Fusarium sulphureum Schlect (isolate 1) were distinguished on the basis of detergent concentration and charge. The induction of water uptake by the cells was found to be an effect of dodecylguanidine acetate (Dodine), a cationic fungicide, at low concentration. At higher concentrations (greater than 5 X 10(-5) M) both the impermeability of the plasma membrane to divalent cations and the ability to accumulate actively L-phenylalanine were lost irreversibly and cell lysis occurred above 5 X 10(-4) M. Sodium dodecyl sulfate eliminated divalent cation impermeability more rapidly than Dodine but was less effective in inhibiting active transport function. An antagonistic effect between cationic and anionic detergents was observed.