Characterization of Storage Proteins in Daucus carota L.: Two Novel Proteins Display Zygotic Embryo Specificity

Although maturation-related proteins are well known in the endosperm of albuminous seeds, an important ques-tion is whether the zygotic embryo possesses its own maturation proteins. We report on the isolation and par-tial characterization of storage proteins of carrot (Daucus carota L. var Nandor) dry achenes and isolated zygotic em-bryos, using one- and two-dimensional electrophoresis tech-niques, HPLC and amino acid sequencing. The presence of a series of abundant polypeptides showing charge hetero-geneity, that are rapidly degraded upon germination, was revealed in the endosperm. These proteins consisted of gly-coproteins, the most abundant of which displayed a molec-ular mass (Mr) of 58,000, albumins of M, 42,000 com-prising at least one /?-l,3-glucanase, and two globulins of M, 90,000 and 50,000-55,000 respectively, the second being an oligomer composed of three subunits of M, 13,000, 20,000 and 30,000. None of these storage proteins iden-tified in the endosperm were detected in zygotic embryos. In contrast, two novel proteins were isolated from zygotic embryos, namely a globulin family of M, 50,000 and p/ 6.3-6.8, which was named "daucin", and a late embry-ogenesis abundant (LEA) protein family of M, 25,000 and p / 6.3-6.6, named "RAB25". Since the latter proteins are apparently absent of the endosperm, these results suggest that the maturation of carrot zygotic embryos requires its own specific set of storage and LEA proteins. Key words: Daucus carota L. — Seed storage protein — Se-quencing — Two-dimensional polyacrylamide gel electro-phoresis — Zygotic embryo. Seeds act as a storage organ for a range of different compounds, such as proteins, oil, starch, minerals, auxin