Synthesis and turnover of proteins and mRNA in germinating wheat embryos

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Abstract
The most prominent methionine-labeled protein made when cell-free systems are programmed with bulk mRNA from dry wheat embryos was identified with what may be the most abundant protein in dry wheat embryos. The protein was purified and has a distinctive amino acid composition, Gly and Glx accounting for almost 40% of the total amino acids. Designated E because of its conspicuous association with early imbibition of dry wheat embryos, the protein and its mRNA are abundant during the early phase (0-1 h) of postimbibition development and easily detected during lag phase (1-5 h), but they are almost totally degraded soon after entry into the growth phase of development, by .apprx. 10 h postimbibition. The most prominent methionine-labeled protein peculiar to the cell-free translational capacity of bulk mRNA from growth phase embryos is not detected as a product of in vivo synthesis. Its electrophoretic properties and its time course of emergence, after 5 h postimbibition development, suggest that this major product of cell-free synthesis may be an in vitro counterpart to a prominent methionine-labeled protein made only in vivo, by growth phase embryos. Designated G because of its conspicuous association with growth phase development, the cell-free product does not comigrate with any prominent dye-stained band in electrophoretic distributions of wheat proteins. The suspected cellular counterpart to G does not comigrate with a prominent dye-stained wheat protein during electrophoresis and although present in particulate as well as soluble fractions of wheat embryo homogenates it is not concentrated in either nuclei or mitochondria, is isolated.