Abstract:

【Objective】The fundamental characteristics of stamen morphogenesis and development were described according to the observation of stamen morphogenesis in Michelia figo. The findings provide valuable basic data for future investigations in plant breeding and evolutionary biology within the Magnoliaceae family.【Method】Using the scanning electron microscopy and paraffin section technology, the stamens of flower buds in M. figo at different growth stages were observed.【Result】The formation pattern of stamen primordium in M. figo was found to be helical and centripetal. Upon the completion of stamen morphogenesis, distinct morphological changes were observed, leading to the formation of a longer anther and a shorter filament. The anther tissue consists of anther septa and four anther locules. Normally, the sporogenous tissue differentiates gradually into microspore mother cells in the anther locule. The microspore mother cell meiosis was not synchronized, and eventually the isobilateral and tertrahedroid microspore tetrads were formed. Then, the free microspore developed into two-celled pollen and a few three-celled pollen. The structure of the anther wall was composed of one layer of epidermis cells, one layer of endothecium cells, two to three layers of middle layer cells, and one layer of secretory tapetum cells. During the development of mature pollen, the tapetum cells disintegrated and disappeared, but some middle layer cells persisted until the anther wall underwent dehiscence. The filaments were surrounded by a single layer of epidermis cells on the outer surface. Internally, the filaments were composed of parenchyma tissue, and a vascular bundle ran through the center toward the connective tissue. There was the cavity structure in the parenchyma of the filaments during the earlier development stage, which later disappeared during the mature stage of the stamen.【Conclusion】The process of stamen morphorgenesis in M. figo is normal compared with other Michelia plant species. The fundamental characteristics observed, including the helical centripetal formation of stamens, asynchronous meiotic division of microspore mother cells, temporal changes of the cavity structure in filaments, predominance of isobilateral tetrads, and two-celled pollen reflected the inherent nature of the Magnoliaceae family.

Key words: Michelia figo, stamen morphorgenesis, filament, anther, microspore tetrad