Biphasic expression of a Vicia faba legumin B gene in developing seeds of transgenic tobacco

Abstract

Summary We analysed the spatial and temporal expression of the Vicia faba legumin gene LeB4 in developing seeds of transgenic tobacco plants by means of in situ hybridization and immunohistostaining. The results indicate that the expression of the LeB4 gene is regulated in embryo and endosperm in a biphasic manner. Legumin accumulation starts during early seed development at low amounts in single cells of the integument. Accumulation proceeds successively in the proembryo, suspensor and endosperm reaching maximum levels in all cells of these organs around 10 to 12 DAP. With the beginning of the heart stage (around 13 DAP) legumin reserves disappear completely from all parts of the seed. The described early phase of legumin accumulation occurs in embryo and endosperm still before the onset of the cell expansion phase in a period of continuous mitotic activity. A second expression phase starts in embryo and endosperm around 18 DAP, as the embryo enters late torpedo stage. Within the embryo the accumulation is restricted to the parenchyma cells of cotyledons and hypocotyl, while the embryonic root and provascular tissue do not accumulate LeB4 protein. In addition, a low percentage ( V. faba for the legumin and vicilin genes during early embryogenesis (Panitz et al., 1995), but differs from that of tobacco 12S globulin genes, which are expressed in the embryo not before the late heart stage.