Ultrastructural studies of somatic embryos of Eucalyptus nitens and comparisons with zygotic embryos found in mature seeds

Although somatic embryogenesis has been observed in tissues from a limited number of Eucalyptus species cultured in vitro, no comparisons have been made of the morphology and structure of eucalypt somatic embryos and zygotic embryos found in mature seeds. We used scanning and transmission electron microscopy, in conjunction with histological analysis, to compare mature zygotic embryos with somatic embryos of the commercially-important temperate eucalypt Eucalyptus nitens. Apart from differences in the nature of the outer coating enclosing both embryo types, somatic embryos of E. nitens were observed to have strong similarities with zygotic embryos in seeds in terms of their overall size, morphology and internal cellular organization. Many cells in both sexually produced and somatic embryos contained numerous lipid-rich globular bodies. The wider significance of these observations is discussed with regard to their potential applications in eucalypt plantation biotechnology programmes. (C) 2000 Annals of Botany Company.