Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulac
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ORIGINAL ARTICLE
Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae) Emilia Brzezicka 1 & Małgorzata Kozieradzka-Kiszkurno 1 Received: 20 June 2020 / Accepted: 2 November 2020 # The Author(s) 2020
Abstract This article describes the development of female gametophyte in Sedum rupestre L. New embryological information about the processes of megasporogenesis and megagametogenesis provided in this paper expand the current knowledge about the embryology of the studied species. S. rupestre is characterized by monosporic megasporogenesis and the formation of Polygonum–type embryo sac. The process of megasporogenesis is initiated by one megaspore mother cell, resulting in the formation of a triad of cells after meiosis and cytokinesis. The functional megaspore, which is located chalazally, is a mononuclear cell present next to the megaspore in the centre of the triad. Only one of the two non-functional cells of the triad is binucleate, which occur at the micropylar pole. In this paper, we explain the functional ultrastructure of the female gametophytic cells in S. rupestre. Initially, the cytoplasm of the gametophytic cells does not differ from each other; however, during differentiation, the cells reveal different morphologies. The antipodals and the synergids gradually become organelle-rich and metabolically active. The antipodal cells participate in the absorption and transport of nutrients from the nucellar cells towards the megagametophyte. Their ultrastructure shows the presence of plasmodesmata with electron-dense material, which is characteristic of Crassulaceae, and wall ingrowths in the outer walls. The ultrastructure of synergid cells is characterized by the presence of filiform apparatus and cytoplasm with active dictyosomes, abundant profiles of endoplasmic reticulum and numerous vesicles, which agrees with their main function— the secretion of pollen tube attractants. Reported data can be used to resolve the current taxonomic problems within the genus Sedum ser. Rupestria. Keywords Antipodal cells . Cytochemistry . Embryo sac . Megagametogenesis . Megasporogenesis . Ultrastructure
Introduction Carpels and stamens are two flower parts responsible for the process of sexual reproduction in angiosperms. These reproductive structures are the production sites of female (embryo sac) and male (pollen grain) gametophytes, respectively. An ovule is an organ that develops in the basal region of carpels called the ovary. It is made of diploid sporophytic cells, including nucellar tissue in which the gametophytic cells undergo differentiation (Raghavan 2000; Bhojwani et al. 2015). In most of the flowering plants, one uninucleate cell, resulting from meiosis (monosporic megasporogenesis), initiates the Handling Editor: Peter Nick * Małgorzata Kozieradzka-Kiszkurno [email protected] 1
Department of Plant Cytology and Embryology, Faculty of Biology, University of Gdańsk, 59 Wita Stwosza St., 80-308 Gdańsk, Poland
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