Cytinus hypocistis L. embryogenesis: Some biological and ultrastructural aspects of fertilization and embryo development

Abstract

The present paper examines some biological and ultrastructural aspects of fertilization and early development of the embryo in Cytitzrrs hypocistis, a parasitic plant belonging to the Ru//lesiaceae. The probable functions of a mucilaginous substance contained i n the ovary and embedding the numerous pollen tubes coming from the style are discussed.I t mas ascertained that pollen tubes pass through the micropyle and enter a synergid pushing, thcir way through the nucellar cells that show swollen walls owing to a probable enzymatic action whose function is to facilitate pollen tube penetration. I t was hypothesized that the secretion of such enzymes is attributable to the numerous pollen present in the ovary or entering the mycropyle.Since, in a11 the ovules observed, synergid degeneration was never found before the arrival of the pollen tube, this degeneration was interpreted as being caused by the material disharged by the pollen tube, rather than being an essential prerequisite for pollen tube penetration into the synergid.Pollen tube content was observed to be made up of an intensely electron-dense substance surrounding many lipidic globules and numerous polysaccharide vesicles that fuse with the pollen tube wall, clearly contributing to its growth.The sequence of the first divisions of the developing embryo was followed and the extreme reduction of the embryo is confirmed.

A new procedure for making observations of embryo morphology in dust-like seeds with rigid coats

“…The embryos of Cytinus hypocistis and C. ruber were similar; they are very small, composed of about ten cells, and surrounded by an endosperm of a few much larger cells (Fig. 1b, c), as has been described previously (Guzowska, 1964;Ponzi and Pizzolongo, 1982;Bouman and Meijer, 1994). Similar features were observed in the anatomical sections ( Fig.…”

“…It is likely that it was not possible to observe the embryos because the marked thickness of the seed coat (Guzowska, 1964; Bouman and Meijer, 1994) impeded entry of the clearing fluid into the seed. Good fixations of fully developed embryos of Cytinus for ultrastructural observations have been impossible due to the same problem (Ponzi and Pizzolongo, 1982). Likewise, neither Treatment 2 nor Treatment 3 allowed embryo visualization.…”