Ultrastructural and cytochemical aspects of female gametophyte development in Sedum hispanicum L. (Crassulaceae)

Abstract

Until now, development of the female gametophyte has been investigated only in some species of Crassulaceae using a light microscope. To the best of our knowledge, this is the first report that describes the process of megasporogenesis and megagametogenesis in Crassulaceae in detail. To achieve this, we performed embryological studies on Sedum hispanicum L. (Crassulaceae). Cytochemical analysis detected the presence of proteins, lipids, and insoluble polysaccharides in individual cells of the gametophyte. The development of the embryo sac conforms to the monosporic or Polygonum-type in anatropous, crassinucellate, and bitegmic ovules. One megaspore mother cell initiates the process of megasporogenesis. Prior to the first meiotic division, the nucleus is centrally located within the meiocyte. Other organelles seem to be distributed evenly over the micropylar and chalazal parts during the development. Most storage reserves detected during megasporogenesis were observed in the megaspore mother cell. Three mitotic divisions within the chalazal functional megaspore resulted in the enlargement of the eight-nucleated embryo sac. In the seven-celled gametophyte, three chalazally located antipodes degenerated. A mature embryo sac was formed by the egg apparatus and central cell. When the antipodes degenerated, both synergids became organelle-rich and more active. The concentration of lipid droplets, starch grains, and proteins increased during megagametogenesis in the growing gametophyte. In the cellular embryo sac, the central cell can be distinguished by its largest accumulation. Our data confirm the hypothesis that plasmodesmata with electron-dense dome are formed during development of the female gametophyte in S. hispanicum and not just during the stages of embryogenesis. We observed these structures in megaspores and coenocytic embryo sac walls. Functions of observed plasmodesmata are discussed.

Development of Embryo Suspensors for Five Genera of Crassulaceae with Special Emphasis on Plasmodesmata Distribution and Ultrastructure

“…Our results confirm the PD in S. atratum and Echeveria lutea are generally similar in structure and distribution to those described and illustrated in Sedum acre and S. hispanicum [24]. Since PD with electron-dense material were noticed also in the Sedum embryo sac components (for details, see [51,52]), an important question, whether specific symplasmic connections in the ovule before/after fertilization are a conserved feature in angiosperms, remains to be addressed.…”

Female gametophyte development in Sedum sediforme (Jacq.) Pau (Crassulaceae): an anatomical, cytochemical and ultrastructural analysis

“…Plasmodesmata with an electron-dense dome were observed only during megagametogenesis in the examined species. Plasmodesmata with adhering electron-dense material distinguish Crassulaceae from other angiosperms, because they were described only during the development of the female gametophyte (Brzezicka and Kozieradzka-Kiszkurno 2018) and embryo (Kozieradzka-Kiszkurno and Bohdanowicz 2010; Kozieradzka-Kiszkurno et al 2011; Kozieradzka-Kiszkurno and Płachno 2012) in this family. In S. hispanicum , characteristic plasmodesmata have been recorded as early as during megasporogenesis.…”

“…Procedure used for transmission electron microscopic observations (TEM) and light microscopic analyses (LM) were the same as those used for the study of ovules (during female gametophyte development and embryogenesis (Czaplejewicz and Kozieradzka-Kiszkurno 2013; Brzezicka and Kozieradzka-Kiszkurno 2018) in another species from genus Sedum . The first samples were fixed in a mixture of 2.5% glutaraldehyde, 2.5% formaldehyde (prepared from paraformaldehyde) in 0.05 M cacodylate buffer (pH = 7.0) and then rinsed with the same buffer and post-fixed overnight in 1% osmium tetraoxide in cacodylate buffer at 4 °C.…”

“…The available documentation is primarily based on schematic drawings (Sharp 1913; Souéges 1927; Mauritzon 1933; Johri et al 1992; Wojciechowicz and Samardakiewicz 1998; Thiede and Eggli 2007). The ultrastucture and cytochemistry of Crassulaceae has only been studied with reference to Sedum hispanicum L. (Brzezicka and Kozieradzka-Kiszkurno 2018). The paper was the first to report the occurrence of a new kind of plasmodesmata (simple plasmodesmata with an electron-dense dome) during the development of the embryo sac.…”

Developmental, ultrastructural and cytochemical investigations of the female gametophyte in Sedum rupestre L. (Crassulaceae)

“…In Crassulaceae, both the integuments have been found to be two-layered (Rombach 1911;Thiede and Eggli 2007), with their growth rate varying depending on the species (Mauritzon 1933). In S. rupestre, the outer integument was found to grow faster than the inner one, as observed in the case of S. sediforme (Brzezicka and Kozieradzka-Kiszkurno 2019), S. hispanicum (Brzezicka and Kozieradzka-Kiszkurno 2018) and most Crassulaceae species (Rombach 1911;Mauritzon 1933). Moreover, two integuments formed the micropyle in the studied species, as has been commonly described for the representatives of the Crassulaceae family.…”