Brzezicka Emilia, Kozieradzka-Kiszkurno Małgorzata
Department of Plant Cytology and Embryology, Faculty of Biology, University of Gdańsk, 59 Wita Stwosza Street, 80-308, Gdańsk, Poland.
Protoplasma. 2018 Jan;255(1):247-261. doi: 10.1007/s00709-017-1155-3. Epub 2017 Aug 24.
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.
到目前为止，仅使用光学显微镜在景天科的一些物种中研究了雌配子体的发育。据我们所知，这是第一份详细描述景天科植物大孢子发生和雌配子体发生过程的报告。为了实现这一目标，我们对西班牙景天（景天科）进行了胚胎学研究。细胞化学分析检测到配子体单个细胞中存在蛋白质、脂质和不溶性多糖。胚囊的发育符合倒生、厚珠心和双珠被胚珠中的单孢子或蓼型。一个大孢子母细胞启动大孢子发生过程。在第一次减数分裂之前，细胞核位于减数母细胞的中央。在发育过程中，其他细胞器似乎均匀分布在珠孔端和合点端部分。在大孢子发生过程中检测到的大多数贮藏物质都存在于大孢子母细胞中。合点端功能大孢子内的三次有丝分裂导致八核胚囊增大。在七细胞配子体中，三个位于合点端的反足细胞退化。一个成熟的胚囊由卵器和中央细胞组成。当反足细胞退化时，两个助细胞都变得富含细胞器且更活跃。在生长中的配子体的雌配子体发生过程中，脂滴、淀粉粒和蛋白质的浓度增加。在细胞型胚囊中，中央细胞因其最大的积累量而得以区分。我们的数据证实了这样一个假设，即在西班牙景天雌配子体发育过程中，而不仅仅是在胚胎发生阶段，形成了带有电子致密穹顶的胞间连丝。我们在大孢子和多核胚囊壁中观察到了这些结构。讨论了观察到的胞间连丝的功能。
