AbstractThe adsorption of some plant growth regulating compounds onto lecithin and equimolar lecithin/cholesterol vesicles and the effect of these substances on the rate of chloride/nitrate and sodium/potassium ion exchange across the vesicular membranes have been examined.On comparing the binding of 2,4‐D, 2,6‐D, 2,4,5‐T and IAA to lecithin vesicles in solution at various pH values it is found that the unionised form of these acids is bound very much more strongly than the ionised form. Compounds having relatively low oil/water partition coefficients such as 2,4‐D, 2,6‐D and 2,4,5‐T are adsorbed onto vesicles, from solutions containing equimolar equilibrium concentrations of the unionised molecules, to markedly different extents (depending on the structure of the lipophilic portion of these molecules). Where the oil/water partition coefficient is higher, as for 2,4‐dichlorophenol and 2‐(2,4‐dichlorophenoxy)ethanol, binding to vesicles may also arise due to non‐specific solution within the hydrocarbon region of the lipid bilayers. The affinity of these compounds for lecithin has also been assessed by noting the extent to which the inclusion of lecithin in the oil phase increases the oil/water partition coefficient. This has shown that affinity for lecithin depends on the structure of both the lipophilic and hydrophilic portions of the molecule.Only the unionised form of the compounds examined had any large effect on ion flux across the vesicle membranes. Significant increases in the rate of chloride/nitrate exchange were obtained on introducing quite high concentrations (0.015 to 1.5 mM) of the compounds 2,4‐D, 2,6‐D, 2,4,5‐T, IAA, and 2,4‐dichlorophenol, but not 2,4‐dichlorophenoxyethanol, to suspensions of lecithin vesicles. Similar flux increases were observed with lecithin/cholesterol vesicles except that more pronounced effects on flux were obtained on adding 2,4‐dichlorophenol and 2,4‐dichlorophenoxyethanol. In contrast 2,4‐D, 2,6‐D, 2,4‐dichlorophenol and IAA had no significant effect on the rate of Na+/K+ion exchange across lecithin vesicles although increases were observed with equimolar lecithin/cholesterol vesicles.Interpretations of these phenomena are suggested and their relevance to plant growth substance effect
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