A Contribution to the Study of the Synthesis of the Reserve Proteins in Ripening Pea Seeds.

Abstract

When unripe seeds of the pea Pisum sativum. were air-dried, most of the water was released; at stage I (of ripeness) 82% of the original wt. evaporated; at stage VII, 55%. The total N, extractable N, non-dialyzable N, dialyzable N, globulin N, and albumin N were determined on NaCl extracts of the peas at each stage. Ultra centrifuge expts. showed that the ratio vicilin/legumin is higher in unripe than in ripe peas. In order to investigate the formation of protein, after harvesting, from low-molecular N constituents in unripe peas, extracts were analyzed ultracentrifugally. The globulin components appeared rather suddently, in the middle of the ripening process (stage III to IV). The amount of high-molecular substance increased 125% at stage IV. These results, for seeds preserved at -20[degree], differ from those for seeds dried at room temp., which show that such seeds contain globulin even at stage I. It follows that ripening continues in seeds separated from the mother plant. During the ripening process in the intact plant, extractable N was constant, albumin N increased at a constant rate, protein N increased mainly during the first half of the ripening, and low-molecular N decreased at the same rate that protein N increased. The mechanism of protein synthesis was discussed. It is believed that the small differences in amino N between fractions containing no well-defined components and those having well-defined components indicate that high-molecular intermediate products are probably involved here in protein synthesis because the formation of large molecules (M= 186,000 and 330,000) from rather large intermediate molecules should give only small changes in amino N. Unripe seeds offer certain advantages to the continued investigation of protein synthesis.