Kinetics of Toluene-induced Leakage of Low Molecular Weight Solutes from Excised Sorghum Tissues

The relationship between toluene concentration and the rate of leakage of solutes from toluene-treated roots and leaves of Sorghum bicolor, L. Moench, was studied to determine the effect of toluene on plant cell membranes. A threshold concentration of 0.2% toluene was needed to induce leakage. Maximal leakage rates were obtained with 0.5% toluene. Low molecular weight solutes, such as amino acids, sugars, and inorganic ions, leaked from treated tissue, while macromolecules, such as protein were retained. The rates at which the low molecular weight solutes diffused from treated cells decreased with increasing molecular weight. At 25 degrees C, treatment of roots and leaves with 0.5% toluene resulted in the quasi-quantitative leakage of solutes within 180 minutes. At 1 degrees C, roots and leaves differed in their response to toluene. The rates of leakage from roots at 1 degrees C were much lower and the total amounts much smaller than at 25 degrees C, while in leaves the difference between the two temperatures was very small.The procedure of treating tissues with 0.5% toluene for 180 minutes at 25 degrees C proved to be a rapid and simple technique for quantitative extraction of water-soluble, low molecular weight solutes from plant cells into the extracting medium while macromolecular constituents are retained inside the cells.