Study of Floral Development and Microsporogenesis in Trochodendron aralioides Sieb. & Zucc. (Trochodendraceae)

• Main Authors: Yu-Chwen Hsu, 許毓純
• Other Authors: Su-Hwa Chen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/p222pb

博士 === 國立臺灣大學 === 植物科學研究所 === 105 === Trochodendron aralioides Sieb. & Zucc. (Trochodendraceae), a tree long considered to lack vessel elements in its wood, was discussed and moved among Magnoliales, Ranunculales, Hamamelidales or Trochodendrales of the basal angiosperms. Recent studies (angiosperm phylogeny group, APG) suggest that T. aralioides should belong to the basal eudicots, and it contains primitive vessels based on scanning electron microscope study. To date, the details of floral development and microsporogenesis of T. aralioides are lack. In the dissertation, the floral development in different stages and the microsporogenesis of T. aralioides are explored to discuss the relationship between T. aralioides and the close clusters in the basal eudicots. For floral development of T. aralioides, it takes about 9 months to develop and the 2-year reproductive cycle of T. aralioides is typical of many temperature trees. In the early development of T. aralioides inflorescences lateral flowers are initiated spirally after the appearance of the floral pherophylls (subtending bracts). The terminal flower is preceded by metaxyphylls and is initiated earlier than the uppermost lateral flowers of the botryoid inflorescence. Small scales seemed as rudimentary perianth organs precede the stamens. These scales are more conspicuous in the terminal flower than in the lateral flowers. In the radially symmetrical terminal flower, the metaxyphylls, the small scales and the stamens are initiated in a spiral acropetally during early development. At anthesis, stamen phyllotaxis appears irregular or approximately whorled as a result of the rapid elongation and irregular slight curvature of the stamen filaments which distorts the originally regular pattern. Finally, the numerous carpels arise simultaneously in a single whorl within stamens. In the stamens, the anther wall is the basic type with an epidermis, an endothecium, three middle layers, and a tapetum. The anther tapetum is glandular and cells are uniseriate. In microsporogenesis of T. aralioides, microspore mother cells undergo meiosis with simultaneous cytokinesis to produce tetrahedral tetrads enclosed within a callose wall. Before development of the protectum, primexine is inserted against the callose, and the plasma membrane is invaginated. Then, the probacula are elongated under the protectum and arise basally from the plasma membrane. The foot layer formation is concomitant with callose wall dissolution. The endexine and intine is initially formed in the vacuolated microspore stage. The foot layer is thick, and the endexine is thin. The foot layer and the endexine are both continuous. Hollow Ubisch bodies are observed on the inner surface of the tapetum in free microspore stage. Consequently, microspores undergo mitosis to produce two unequal cells, a large vegetative cell and a small generative cell. Pollen grains are tricolporate, reticulate and 2-celled at the time of shedding. Base on the floral development and microsporogenesis of T. aralioides, we compared those with the other basal eudicots. The bottle-shaped, the unicellular stigmatic papillae and the long, decurrent stigma of basal united carpels of T. aralioides are similar to those of the Buxales. Therefore, the persisting floral characteristics of T. aralioides support the phylogenetic relationship with the cluster of basal eudicots in APG IV.