Changes in the Contents of Free and Protein Amino Acids in Tobacco Seeds and Placentae during Maturation

Abstract

Changes in the levels of protein and free amino acids in the seeds and placentae of Nicotiana tabacum were studied during seed development. Seed maturation was completed 24 days after anthesis. During maturation, protein rapidly accumulated in the seeds between the 6th and 18th day, along with an appreciable compositional change in the protein amino acids as the proportions of glutamic acid and arginine increased. The amount of free amino acids in the seeds gradually decreased throughout maturation. The major free amino acid on the 6th day after anthesis was glutamine, which then drastically decreased between the 6th and 12th day with increases of glutamic acid, proline, arginine and alanine. The latter amino acids decreased thereafter until the 24th day. On the other hand, the amount and composition of the proteins in the placentae did not change significantly throughout seed maturation. In the early stage of development, the major free amino acids in the placentae were glutamine, asparagine and glutamic acid, while in the later stage asparagine was most abundant.