CHARACTERIZATION OF STORAGE PROTEINS IN DAUCUS-CAROTA L - 2 NOVEL PROTEINS DISPLAY ZYGOTIC EMBRYO SPECIFICITY

Although maturation-related proteins are well known in the endosperm o f albuminous seeds, an important question is whether the zygotic embry o possesses its own maturation proteins. We report on the isolation an d partial characterization of storage proteins of carrot (Daucus carot a L. var Nandor) dry achenes and isolated zygotic embryos, using one-a nd two-dimensional electrophoresis techniques, HPLC and amino acid seq uencing. The presence of a series of abundant polypeptides showing cha rge heterogeneity, that are rapidly degraded upon germination, was rev ealed in the endosperm. These proteins consisted of glycoproteins, the most abundant of which displayed a molecular mass (M-r) of 58,000, al bumins of M-r 42,000 comprising at least one beta-1,3-glucanase, and t wo globulins of M-r 90,000 and 50,000-55,000 respectively, the second being an oligomer composed of three subunits of M-r 13,000, 20,000 and 30,000. None of these storage proteins identified in the endosperm we re detected in zygotic embryos. In contrast, two novel proteins were i solated from zygotic embryos, namely a globulin family of M-r 50,000 a nd pI 6.3-6.8, which was named ''daucin'', and a late embryogenesis ab undant (LEA) protein family of M-r 25,000 and pI 6.3-6.6, named ''RAB2 5''. Since the latter proteins are apparently absent of the endosperm, these results suggest that the maturation of carrot zygotic embryos r equires its own specific set of storage and LEA proteins.