Callose deposition analysis with special emphasis on plasmodesmata ultrastructure during megasporogenesis in Sedum (Crassulaceae).

In this study, the results of the first detection of callose within the ovules of the representatives of the family Crassulaceae are presented. This study was carried out on three species of the genus Sedum. Data analysis showed differences in the callose deposition pattern between Sedum hispanicum and Sedum ser. Rupestria species during megasporogenesis. Callose was present mostly in the transversal walls of dyads and tetrads in S. hispanicum. Furthermore, a complete loss of callose from the cell walls of the linear tetrad and a gradual and simultaneous deposition of callose within the nucellus of S. hispanicum were observed. The findings of this study showed the presence of hypostase with callose in the ovules of S. hispanicum, which is not common in other angiosperms. The remaining species tested in this study-Sedum sediforme and Sedum rupestre-showed a typical, well-known callose deposition pattern for plants with the monospore type of megasporogenesis and the Polygonum type of embryo sac. The functional megaspore (FM) in all studied species was located most chalazally. FM is a mononuclear cell, which wall is callose-free in the chalazal pole. The study presents the causes of different patterns of callose deposition within Sedum and their relationship with the systematic position of the study species. Moreover, embryological studies present an argument for excluding callose as a substance that forms an electron-dense material near the plasmodesmata in megaspores of S. hispanicum. This research expands the knowledge about the embryological processes of succulent plants from the family Crassulaceae.

Embryogenesis in Crassulaceae: structural aspect of suspensor development / Embriogeneza u Crassulaceae: strukturalny aspekt rozwoju wieszadelka.

The suspensor in the majority of angiosperms is an evolutionally conserved embryonic organ functioning as a conduit that connects ovule tissues with the embryo proper for nutrients and growth regulators flux. In this article the present knowledge on the embryo-suspensor ultrastructure and function in representatives of Crassulaceae genera: Sedum, Jovibarba, Sempervivum, Aeonium, Monanthes, Aichryson and Echeveria. The role of the suspensor in the transport of nutrients from the tissues of the ovule to the proper embryo is confirmed by the structure of the basal cell, especially the nature of the micropylar part of its wall, the "transfer wall". The basal suspensor cell is a site of intense metabolic activity. The special attention is paid to the plasmodesmata. The correlation between types of suspensors and structure of plasmodesmata was investigated. Final conclusions are given and the presented data summarized.

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

Available documentation about the development of the female gametophyte of Crassulaceae is very limited. The aim of this study was to extend the embryological knowledge of Crassulaceae by analysing the development of the embryo sac in Sedum sediforme. Transmission electron microscopy and light microscopy including Nomarski optics (DIC) were used to observe individual stages of female gametophyte development. Cytochemical staining enabled detection of lipids, insoluble polysaccharides and proteins in gametophyte cells during their formation. Their increased accumulation was observed during nucellar cell and unfunctional cell degeneration in the embryo sac at the coenocytic and cellular stages (megagametogenesis). The female gametophyte develops in anatropous, bitegmic and crassinucellate ovules. The mature embryo sac is built of seven cells but after antipodes degeneration it is formed by the egg apparatus and a central cell. The monosporic Polygonum type was observed. One megaspore mother cell (MMC) formed three cells after meiosis. A triad was formed from a functional megaspore (placed chalazally), one uninucleate megaspore and a binucleate cell located at the micropylar end. Plasmodesmata with adhering electron-dense dome were noticed in walls of the coenocytic embryo sac and in the outer walls of ephemeral antipodes. Moreover, similar to synergids, antipodes form wall ingrowths. Here, we report new structural features of the antipodal cells (the presence of plasmodesmata with an electron-dense dome) which have not been described before. This new structural observation indicates that these cells participate in substance transport and that this process can probably be additionally regulated.

New data about the suspensor of succulent angiosperms: Ultrastructure and cytochemical study of the embryo-suspensor of Sempervivum arachnoideum L. and Jovibarba sobolifera (Sims) Opiz.

The development of the suspensor in two species - Sempervivum arachnoideum and Jovibarba sobolifera - was investigated using cytochemical methods, light and electron microscopy. Cytological processes of differentiation in the embryo-suspensor were compared with the development of embryo-proper. The mature differentiated suspensor consists of a large basal cell and three to four chalazal cells. The basal cell produces haustorial branched invading ovular tissues. The walls of the haustorium and the micropylar part of the basal cell form the wall ingrowths typical for a transfer cells. The ingrowths also partially cover the lateral wall and the chalazal wall separating the basal cell from the other embryo cells. The dense cytoplasm filling the basal cell is rich in: numerous polysomes lying free or covering rough endoplasmic reticulum (RER), active dictyosomes, microtubules, bundles of microfilaments, microbodies, mitochondria, plastids and lipid droplets. Cytochemical tests (including proteins, insoluble polysaccharides and lipids are distributed in the suspensor during different stages of embryo development) showed the presence of high amounts of macromolecules in the suspensor cells, particularly during the globular and heart-shaped phases of embryo development. The protein bodies and lipid droplets are the main storage products in the cells of the embryo-proper. The results of Auramine 0 indicate that a cuticular material is present only on the surface walls of the embryo-proper, but is absent from the suspensor cell wall. The ultrastructural features and cytochemical tests indicate that in the two species - S. arachnoideum and J. sobolifera - the embryo-suspensor is mainly involved in the absorption and transport of metabolites from the ovular tissues to the developing embryo-proper.

Are there symplastic connections between the endosperm and embryo in some angiosperms?--a lesson from the Crassulaceae family.

It is believed that there is symplastic isolation between the embryo (new sporophyte) and the endosperm (maternal-parental origin tissue, which nourishes the embryo) in angiosperms. However, in embryological literature there are rare examples in which plasmodesmata between the embryo suspensor and endosperm cells have been recorded (three species from Fabaceae). This study was undertaken in order to test the hypothesis that plasmodesmata between the embryo suspensor and the endosperm are not so rare but also occur in other angiosperm families; in order to check this, we used the Crassulaceae family because embryogenesis in Crassulaceae has been studied extensively at an ultrastructure level recently and also we tread members of this family as model for suspensor physiology and function studies. These plasmodesmata even occurred between the basal cell of the two-celled proembryo and endosperm cells. The plasmodesmata were simple at this stage of development. During the development of the embryo proper and the suspensor, the structure of plasmodesmata changes. They were branched and connected with electron-dense material. Our results suggest that in Crassulaceae with plasmodesmata between the endosperm and suspensor, symplastic connectivity at this cell-cell boundary is still reduced or blocked at a very early stage of embryo development (before the globular stage). The occurrence of plasmodesmata between the embryo suspensor and endosperm cells suggests possible symplastic transport between these different organs, at least at a very early stage of embryo development. However, whether this transport actually occurs needs to be proven experimentally. A broader analysis of plants from various families would show whether the occurrence of plasmodesmata between the embryo suspensor and the endosperm are typical embryological characteristics and if this is useful in discussions about angiosperm systematic and evolution.

Clumping and dispersal of chloroplasts in succulent plants.

Plants have evolved various photoprotective mechanisms to mitigate photodamage. Here we report the diurnal movement of chloroplasts in the leaves of succulent crassulacean acid metabolism (CAM) plants under combined light and water stress. In leaves of water-stressed plants, the chloroplasts became densely clumped in one or sometimes two areas in the cytoplasm under light and dispersed during darkness. The chloroplast clumping resulted in leaf optical changes, with a decrease in absorptance and an increase in transmittance. The plant stress hormone abscisic acid induced chloroplast clumping in the leaf cells under light. We suggest that the marked chloroplast movement in these CAM plants is a photoprotective strategy used by the plants subjected to severe water stress.