Uptake of Amino Acids and Other Organic Compounds by Lemna paucicostata Hegelm. 6746

Abstract

A survey of the capacity of L. paucicostata to take up organic compounds such as might be present in the natural environment of this plant identified 8 discrete transport systems. Reciprocal inhibition studies defined the preferred substrate for these systems as follows: neutral L-.alpha.-amino acids, basic amino acids, purine bases, choline, ethanolamine, tyramine, urea and aldohexoses. Each of these systems takes up its preferred substrates at high rates. At low concentrations, each Lemna frond during each minute takes up amounts which would be found in volumes ranging from 0.4 (tyramine) to 3.9 (urea) times its own volume. The 2 system for amino acid transport both showed kinetics of the biphasic type, so that uptake by each can be described as the composite result of 2 Michaelis-Menten processes. The neutral amino acid system neither transport basic amino acids nor is inhibited by these compounds. The basic amino acid system does not tranport neutral amino acids but is strongly inhibited by some, but not all, of these compounds. The maintenance of these active, specific and discrete systems in Lemna suggests they play important roles permitting this plant utilize organic compounds occurring naturally in its environment.