Microsporogenesis and male gametophyte formation
Anther morphology: Tupistra Chinensis flowers with 6 stamens, base of filaments enlarged, and the enlarged part is adnate to the inner part of perianth, 1-2mm long. Anthers ovate, incurved, each stamen with 4 pollen sacs, butterfly-shaped in cross section, very few with 2 pollen sacs.
Anther wall development: In the initial stage of stamen development in Tupistra Chinensis, the stamen primordium is formed. The cells located under the epidermis of the four corners of the stamen primordia differentiated to produce male sporogenous cells. The protosporium divides peripherally, producing primary pericytes and primary sporogenous cells. The primary peripheric cells divide once to form inner and outer layers of peripheral cells, and each of the two layers of peripheral cells divides once again to form 4 layers of cells. The outer layer of cells forms the inner wall of the anther wall, the innermost layer of cells near the anther forms the tapetum cells, and the middle two layers of cells form the middle layer of the anther wall. At the pollen mother cell stage, the anther wall is completely differentiated and consists of epidermis, inner wall, middle layer and tapetum. It can be known that the anther wall layer of Tupistra Chinensis developed into the basic type. During the meiosis stage of microspore mother cells, the cells of the tapetum were obviously larger than the other cells of the anther wall, and the cells differentiated into larger vacuoles with obvious nuclei. From late tetrad to unicellular anther stage, tapetal cells began to disintegrate and degenerate, and to mature 2-cell pollen stage, tapetal cells completely disintegrated, and the anther wall was only composed of epidermis and fibrous layer. The cells of the fibrous layer of the anther wall were thickened in bands, but the cells of the fibrous layer at the junction of the two anthers on the same side were not thickened, and the last two anthers were connected. As the lip cells split, the anther sac splits and the pollen grains are shed.
Microspore formation: Tupistra Chinensis microspore mother cells are larger in size, with large nuclei and dense cytoplasm. During meiotic prophase, chromatin filaments appear in the nucleus of the microspore mother cell. Microspore mother cells undergo meiosis and form dyads and tetrads in turn. Tetrads are left-right symmetric type, tetrad microspores with dense cytoplasm and a large central nucleus.
Formation of the male gametophyte: After the four microspores in the tetrad separate from each other, a unicellular pollen grain is formed. The early single-cell pollen grains were irregular in shape, and most of them were concave inward on one side. With the development of the pollen grain, the single-cell pollen gradually becomes round and increases in volume, and the nucleus is located in the center of the pollen grain. While the volume of single-cell pollen increases, the shape of the cell becomes oval, a large vacuole is formed in the cell, and the nucleus of the pollen cell moves to one end of the cell. This is the uninucleate marginal stage. The nucleus of the unicellular pollen grain undergoes an uneven mitosis near the pollen cell wall on one side to form 2 daughter nuclei, and a cell wall forms between the 2 daughter nuclei to divide it into 2 cells, namely: vegetative cells and germ cells. Among them, the vegetative cells are larger, located in the center of the pollen grain, spherical; the reproductive cells are small, close to the pollen wall. Then the germ cells move from the position close to the cell wall to the central part of the pollen cell, located in the cytoplasm of the pollen vegetative cell, forming 2-cell pollen.
Megasporogenesis and female gametophyte formation
Megasporogenesis: Tupistra Chinensis pistil ovary 3 carpels 3 locules, 2 anatropic ovules in each locule. During the early development of the ovary, the cells below the epidermis in the placenta divide and proliferate to form the ovule primordia. The cells of the ovule primordium continue to divide and differentiate, the cells at the front develop into the nucellus, and the base develops into the nucellus. Underneath the epidermis at the top of the nucellus, female prospore cells differentiate. The sporogenous cell undergoes a meridian division to form a peripheral cell and a sporogenous cell, and the sporogenous cell develops into a megaspore mother cell. When the ovule develops to the stage of megaspore mother cell, two layers of integument are differentiated at the base of the nucellus, the inner integument occurs before the outer integument, and the cells of the integument continue to divide and grow upward to surround the nucellus, forming the integument at the top hole. With the growth and development of the ovule, the ovule gradually bends from the upright growth to one side, and finally forms an anatropic ovule. The megaspore mother cell forms dyads through the first meiotic division, but only one dyad cell close to the chalazal end undergoes the second division to produce 2 daughter nuclei, while the dyad cell at the micropylar end does not undergo the second meiotic division Secondary meiosis, regression disappears. The dyad cells at the chalazal end undergo the second meiosis to produce 2 daughter nuclei without cell wall differentiation, thus directly forming a dinuclear embryo sac.
Formation of female gametophyte: After meiosis, two megaspores are formed at the chalazal end of the embryo sac, which directly develop into a dinuclear embryo sac. The two nuclei of the dinucleate embryo sac undergo 2 consecutive mitosis at the chalazal end and the micropylar end to form a quadrinucleate embryo sac and an octanucleate embryo sac respectively. At this stage, the volume of the embryo sac increases rapidly, and some nucellus cells degenerate and disintegrate to form a mature embryo sac. At the micropylar end of the mature embryo sac, an egg organ is differentiated, which contains 1 egg cell and 2 synergid cells, and the central cell is in the middle of the embryo sac. During the development of Tupistra Chinensis embryo sac, the three antipodal cells at the chalazal end degenerated earlier, so that no antipodal cells could be observed in the mature embryo sac. It can be seen from the above development process that the embryo sac development type of Tupistra Chinensis is bisporous allium type. Oocytes and synergids have distinct cell polarity. The nucleus and cytoplasm of the egg cell are mainly distributed at the chalazal end of the cell, while the micropyle end is divided into a larger vacuole. The cell polarity of the 2 synergids is opposite to that of the oocyte. The upper and lower pole nuclei are located in the center of the mature embryo sac, surrounded by a large vacuole. Before fertilization, the 2 polar nuclei merge into the central cell of the secondary nucleus.
