Studies on Somatic Embryogenesis of Coffee by Scanning Electron Microscope.

Development of somatic embryos from coffee leaf explants has been studied in detail by scanning electron microscopy (SEM). Friable embryogenic callus is formed by single spherical cell aggregates of about 20μm diameter. They are the putative initial cells of somatic embryos or embryo mother cells. The fine structure of somatic embryos was clearly identified during the following sequential developmental stages : single spherical cell, early globular shape with conspicuous suspensor, typical globular shape, elongated shape, early heart shape, typical heart shape, torpedo shape, and finally cotyledonary stage embryo with well-developed suspensor. The high frequency of somatic embryos was found in callus tissues derived from mature leaves under a two-step culture method. Low frequency somatic embryogenesis was found on the leaf edges associated with very small callus formation. Low frequency somatic embryos were observed only in young leaves under the one-step culture method. In this SEM investigation, it is demonstrated that the sequential events leading to coffee somatic embryogenesis arise through one unicellular pathway derived from coffee somatic embryo mother cells. A schematic representation of the sequential stages of coffee somatic embryo development is provided.