Ion Transport Characteristics of Grape Root Lipids in Relation to Chloride Transport

Ion transport properties of grape root lipids were measured as liquid-membrane permeability. Phosphatidylcholine exchanged chloride very slowly against carbonate and bicarbonate but more rapidly against nitrate, phosphate, and sulfate. Exchange of chloride against nitrate was rather low for the phosphatidylcholine and phosphatidylethanolamine lipid fractions; monogalactose diglyceride was by far the most effective chloride transporter studied. Comparison between the lipid composition of the roots of the 5 grape rootstocks and the chloride transport capacity of the specific membranes strongly suggests that, indeed, the chloride transport capacity of the lipids present in the membranes of the root cells accounts for the observed differences in chloride transport to the leaves. Whereas monogalactose diglyceride had a high chloride transport capacity, compared with phosphatidylcholine, the reverse was true for exchange of sodium against potassium. Thus, phosphatidylcholine has more the properties of a cation exchanger, and monogalactose diglyceride those of an anion transporter.