Amino Acid Pools in Perennial Plants at the Wintering Stage and at the Beginning of Growth 1

Free amino acids in plants at the stages of wintering and the beginning of growth were analyzed under natural conditions. From the major amino acid contents, the pools were separated into the following types: 1) a group which accumulated arginine alone (11 out of 31 samples); 2) a group which accumulated proline alone (4 out of 31) and 3) a group which accumulated arginine and proline (15 out of 31). Comparison of the compositions at stages of wintering and the beginning of budding indicated that the increase in the proline level is related to the onset of growth. Synthesis of arginine and roline and translocation of proline would seem to indicate that these substances play the role of filling-in materials in any particular tissue. For plants which require chilling temperatures for growth, the accumulation of arginine and proline was considered to be a normal event, since temporal changes in the major amino acids from arginine (and proline) through glutamate to asparagine plus aspartate were generally observed. Uncoupling between amino acid syntheses and the commencement of development was also observed in plants which were housed in a greenhouse during winter. A possible function of proline as a natural cryoprotectant is discussed.