AMINO ACID AND AMIDE METABOLISM IN THE HULLS AND SEEDS OF DEVELOPING FRUITS OF GARDEN PEA, PISUM SATIVUM L.: III. HOMOSERINE.

Pea plants (Pisum sativum L. cv. Melbourne Market), each with a single developing pod, were pulse-fed with [ C]homoserine supplied through the cut stem at stages of pod development ranging from 12 to 21 d after full blossom. The pods were removed after 24 h and the hulls and seed components were frozen for later analysis. Except at the youngest stage, or unless the pod had been enclosed in foil to prevent the development of chloroplasts, the seeds received a higher proportion of total label in the fruit (about 60%). The distribution of label in soluble metabolites of the hull, seedcoats, embryo sac liquid and embryo was determined by paper chromatography and radioautography. The results indicate turnover of homoserine within the hull, and confirm that the seedcoats are responsible for a shift in metabolism leading to secretion of threonine into the embryo sac instead of homoserine.