Histodifferentiation of somatic embryos in cotyledons of pineapple guava (Feijoa sellowiana Berg)

Summary

Somatic embryos of pineapple guava (Feijoa sellowiana Berg, Myrtaceae) were induced particularly well from the adaxial face of the cotyledons of zygotic embryos cultured on MS medium containing 1.0 mg/l 2,4-D and 0.3 M sucrose. Somatic embryos were never obtained from globular and heart-shaped zygotic embryos and embryos at the torpedo stage produced somatic embryos at lower frequencies than mature zygotic embryos. At the time of explantation, cotyledonary cells were rich in storage proteins and lipids but no starch was found. After the first 5 days of culture most of the reserves had been mobilized in cotyledons of germinating embryos, but were still present in large amounts in cotyledons undergoing embryogenie induction. In contrast to cotyledons following the normal pattern of development, cells of embryogenically-induced cotyledons accumulated starch, especially those cells not involved in the embryogenie process. Two patterns of somatic embryo differentiation were observed: (1) from single epidermal cells or (2) from groups of meristematic cells near the adaxial surface. Comparative observations on cotyledons from germinating embryos and those undergoing embryogenesis suggest that the meristematic layer arises as the result of successive divisions of cells that, under normal conditions, would form the palisade parenchyma. These were the only mesophyll cells that showed mitotic divisions during the normal development.