Further studies of intermediary metabolism in radish cotyledons. The utilization of glycine, glyoxylate, and acetate by tissue disks

摘要

Micromolar quantities of14C-labelled glycine, glyoxylate, and acetate were metabolized by disks of 11-day-old radish cotyledons. Time-course experiments with illumination showed that both glycine and glyoxylate were extensively converted into serine, into various organic acids, and to a lesser extent into sugars. Pulse-chase experiments in which glycine-2-14C was used indicated that the major labelled products of 30-min pulse feedings rapidly lost14C on incubation of the tissues in unlabelled glycine. As these losses were not accompanied by corresponding accumulations of14C in the medium, they were largely attributed to extensive metabolic turnover.A comparison of glycine and glyoxylate pulse feeding experiments in light and dark showed that slightly lower percentages of both substrates were incorporated into the sugars in the dark. Incorporation of glyoxylate-14C into the sugars was markedly stimulated in both light and dark experiments when the tissues were simultaneously incubated with unlabelled glycine. It is concluded that in radish cotyledons, as in leaves, glyoxylate and glycine are both effective precursors of serine. The synthesis of sugars from these substrates appears to occur by a pathway essentially different from the glycollate pathway.