Protein Synthesis in Imbibing Wheat Embryos

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Abstract
Polypeptides synthesized by imbibing wheat embryos were compared with those made by cell-free extracts programmed with bulk poly(A)-rich RNA from dry wheat embryos. Newly synthesized polypeptides, labeled with [35S]methionine, were resolved by 1-dimensional and 2-dimensional electrophoresis and then records of the separations were prepared by fluorography. When programmed by bulk poly(A)-rich RNA from dry wheat embryos, a micrococcal nuclease-[EC 3.1.4.7]-treated rabbit reticulocyte lysate synthesizes an array of polypeptides which is broadly similar to that formed when a wheat germ extract is programmed with the same RNA. Polypeptides made in both homologous and heterologous cell-free systems, under the direction of bulk poly(A)-rich RNA from dry wheat embryos, are broadly similar to those formed during early (0-40 min) imbibition of dry wheat embryos. As imbibition progresses beyond 40 min, there are profound changes in the 1-dimensional and 2-dimensional electrophoretic distributions of newly made polypeptides present in the 23,000 .times. g supernatant fraction of cell-free homogenates; characteristically, low MW and basic polypeptides comprise a diminishing proportion of the total polypeptides as imbibition progresses beyond 40 min. Ribosomal proteins are conspicuous among the proteins formed during early imbibition and especially prominent among the products formed when homologous cell-free polypeptide synthesis is programmed by bulk poly(A)-rich RNA from dry wheat embryos.