Cyto-histological Studies on Somatic Embryos of Coffee: Ultrastructural Aspects.

Abstract

A histological and ultrastructural study of somatic embryogenesis in coffee embryos was made by light microscopy and transmission electron microscopy. A comparative study on somatic and zygotic embryos of coffee was also performed. The cells in the suspensor region of somatic embryos were filled with large-and small-sized granules containing polyphenol substances stainable in black. The granule size increased until the elongated-embryo stage and thereafter it decreased with embryo development. Such granules were very small in cotyledonary embryo cells. The continuous and discontinuous cuticular layers were detected on both the somatic, globular embryos and the zygotic proembryos by treatment of iodine/potassium iodide-sulfuric acid-silver proteinate. This preparation also permitted the identification of the deposition of fine silver particles inside the polyphenol granules. In addition the plastids were filled with several starch grains of large and small sizes. Similarly, cells of the zygotic proembryos and young embryos were also filled with polyphenol granules and plastids containing starch grains. It is interesting to note that mucilaginous materials cover the surface of both the embryogenic callus and the suspensor region of somatic embryos and are also present in the intercellular spaces of these tissues. These materials were also covering zygotic embryos situated in the embryo cavity of seeds. These observations led to the conclusion that the somatic and zygotic embryos have several similarities at the ultrastructural level.