A new model membrane system for the investigation of penetrative properties of plant growth substances

A new model membrane system has been developed which simulates in many ways the behaviour of a plant cell membrane. It is very suitable for studying the penetration and associated effects of plant growth substances because of its large size (4.9±0.3 cm2), its ease of preparation and its reproducible properties. It consists of a Millipore filter disc impregnated with egg yolk lecithin, n‐octanol and n‐tetradecane. The effect of a number of plant growth and allied compounds on membrane conductivity at 25±0.5°c has been assessed by the addition of various concentrations of these substances to the solutions (0.01 M‐NaCl) on each side of the membrane. Certain compounds present in the solutions (pH 3.0) in the concentration range 10−4 M to 10−3 M considerably reduced the membrane conductivity. This effect was seen to be related to the structure of the hydrophobic portion of the molecule. The flux through the membrane at 25±0.5°c of various organic substances (2,4‐D, benzoic acid, benzyl alcohol, benzamide and benzaldehyde) was measured for membranes containing no lecithin and compared with the flux obtained in comparable experiments, with lecithin present in the membrane. The presence of lecithin increased the flux, and the percentage increase was used to assess in each case the part played by lecithin in transport. The flux of 2,4‐D was much greater at low pH values. A possible interpretation of these phenomena is suggested.