Amino Acid Metabolism in Nongrowing Environments in Higher Plants

During winter season, growth of biennial and perennial plants was virtually halted. Amino acid analyses of 74 samples of woody and herbaceous plants including grasses and winter wheat showed following results. In innately dormant plants, synthesis and accumulation of free amino acids were completed in fall and next changes occurred in the following spring. In plants under enforced dormancy, a different reaction from that of growing season occurred and continued during wintering under snow. 1. Amino acid pools - From major amino acid contents of the pool, pools were separated into five types: a group which accumulated 1) arginine, 2) arginine and proline, 3) proline, 4) glutamine and glutamate and 5) asparagine, respectively. 2. Inorganic nitrogen assimilation - InDactylis glomerata, about 20µmoles of NH3 g(-1) fresh weight were converted into amide nitrogen of glutamine during winter. 3. Increase of the pool concentrations - In winter wheat (cv. horoshirikomugi), the level in March was more than twice that of November. 4. Changes in the pool composition - (Examples), 1) decrease of arginine inAgrostis alba, 2) decrease of asparagine and increase of arginine inMedicago sativa, 3) increase of asparagine in winter wheat. 5. Accumulation of particular amino acids - Histidine inArctium lappa, threonine inArmoracia rusticana and serine inMedicago sativa. Since the reaction appeared to proceed at extremely slow rates over the winter season, amino acid analysis only seemed to be feasible to assess the extent of amino acid accumulation in the pool.