Organic Acid Metabolism and Ion Absorption in Roots

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Abstract
Ionic balance in excised plant roots during preferential absorption of cations or anions is maintained primarily by exchange of previously absorbed ions or by metabolic gain or loss of malic acid anion within the root in stoichiometric proportions. The exchange reaction appears to predominate in older root material, whereas the malic acid changes are most significant in week old barley seedling roots. Essentially all of the organic acids in barley seedling roots (Sacramento variety) were quantitatively determined by means of silica gel column chromatography. Malic and acetic acids predominate with lesser quantities of fumaric, succinic, and citric acids and small amounts of other TCA cycle acids present. Acetic acid is present in barley seedling roots to the extent of nearly 1% on a dry weight basis. It occurs in a bound insoluble form and is readily liberated by mild acid hydrolysis. Its role in absorption or metabolism is not known.