Germin. Compartmentation of the protein, its translatable mRNA, and its biosynthesis among roots, stems, and leaves of wheat seedlings

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Abstract
(1) Onset of growth during germination of the isolated wheat embryo is allied with the emergence of a protein we have called germin. This study was undertaken to learn if germin is present and synthesized in the root, stem, and leaf during postgerminative growth of the wheat seedling.(2) Seedlings were grown from mature wheat grains on water-soaked filter paper and organs excised at various times were pulse labeled with [35S]methionine. Germin is synthesized in all organs at all times between 1.5 and 7 days.(3) During early seedling development (1.5 days), the fraction of [35S]methionine incorporated into germin, relative to other proteins, is much greater in the case of stem than other organs, either in vivo or when cell-free protein synthesis is directed by bulk RNA from different organs.(4) During late seedling development (4–7 days), when root growth is greater than stem growth, total isotope incorporation into germin is much greater in roots than stem.(5) Quasi-quantitative estimates of germin in pepsin-treated soluble fractions of homogenates were made by visual comparison of dye binding when gels were stained by Coomassie blue. The quantity of germin (ca. 1 mg/100 g) keeps pace with growth in spite of a 100-fold increase in fresh weight during transformation of the germinating embryo into a 7-day seedling.(6) During early seedling growth (1.5 days), germin is concentrated in the stem, but later (7 days), after extensive growth of the root but not the stem, the amount of germin in the root is about 1/2 and in the leaf is about 1/10 as great as in stem, on a fresh-weight basis, but more nearly equal on a per-organ basis owing to high mass proportions of the leaf and root relative to stem.(7) The dye-staining technique following pepsin treatment of soluble proteins has been used to detect germin in the stems of other cereal (rye, barley, oat) seedlings (3–8 days).