Free amino acid changes associated with vernalization of wheat

Abstract

Changes in the free amino acids in the leaf tissues of a spring and an obligate winter wheat were determined. The plants were grown for 0–5 weeks at 2° and at 25°. Seventeen known and at least seven unidentified ninhydrin positive components were detected. Only glutamic acid and lysine were more abundant at 25° than at 2°. At 2° the spring variety contained higher quantities of 14 of the amino acids, and the winter wheat contained higher quantities of alanine, glutamic acid, proline and arginine; proline being outstanding. At 25° the differences were not so marked. A general increase in the neutral and acidic amino acids in both varieties grown at 2° during the first 2 weeks was followed by a rapid decline during the subsequent week. Usually, a gentle to rapid increase followed during the final 2 weeks of growth. The basic amino acids did not follow this general pattern. The effect of growing temperature on the amino acid levels was usually greater than the varietal effect of spring vs. winter wheat. But large differences between these varieties were detected in the levels of phenylalanine, proline, tryptophan and unknown No. 1. Glutamine and asparagine + serine, which were all eluted together, usually accounted for 30–80 per cent of the total free amino acids. Alanine and proline were both very high in the cold-grown winter wheat; alanine contributed 30–35 per cent and proline 16–18 per cent of the total free amino acids during the latter part of the growth period. Similar and parallel changes were observed in some of the amino acids during the 5 weeks of growth, but there was no apparent correlation between these patterns of similar change and the common biosynthetic families of amino acids. The patterns and rather dramatic changes in levels of several of the soluble nitrogen compounds may well be significant clues to biochemical mechanisms involved in vernalization of wheat. Components which this study suggests may be of particular interest are proline, glutamine and asparagine, ammonia plus overlapping unknowns, other basic amino acids and an acidic substance tentatively suggested to be glutathione.