| Summary: | 碩士 === 國立成功大學 === 生物學系 === 87 === The floral development and microsporogenesis of castor, Ricinus communis L., were studied by electron microscopy, light microscopy, and histochemical analysis. Furthermore, the development of microspore in stamen and staminode of pistillate flower were compared.
The spike inflorescence consists of dichasia that is a new type of inflorescence, since it is not mentioned in literatures. In the early stage of development, both pistillate and staminate flowers have the same initiation, the development of a prophyll and a ring calyx. The protrusion on floral apex in pistillate and staminate flowers were distinguishing. There are three definited protrusions in the gynoecium, while the protrusions are several and indefinited in the androecium. At the late development stage, the three protrusions of gynoecium are differentiated into three styles and six stigmas, and there are soft spines on the ovary wall. On the other hand, the several protrusions of androecium are differentiate into numerous stamens with filaments partially connate. Furthermore, some unusual structures initiate and grow around the calyx and the base of the ovary in pistillate flowers. These structures are variable in shape and size. Some are stamen-like, some are gynoecium-like, and the others are bisexual flower-like.
The microsporogenesis can be distinguished into eleven stages. The anther wall layers occurred as dicotyledonous type and were composed of epidermis, endothecium, middle layers (1-2 layers) and tapetum. In the mature pollen stage, most of the anther walls were wilt except the fibrous endothecium. The cytokinesis after meiosis occurred simultaneously by the invasion of callose wall, then a tetrahedral tetrad enclosed in the callose wall was produced. Mature pollen grain is 2-cell and a lot of starch grains and lipid droplets deposite in its cytoplasm. Moreover, some pollenkitt can be found on the exine of the mature pollen.
The formation of pollen wall started during the early tetrad stage. At first, the plasma membrane of microspores protruded and some materials were deposited on the protrusion of plasma membrane.
The secretory tapetum is 2-nucleus and composes of numerous mitochondria, dictylsomes, endoplasmic reticulum and orbicules on its plasma membrane. The tapetal cell degenerate in the mature pollen stage.
The structure of anther wall, tapetum and exine development in the staminodes of pistillate flowers were some what different to the stamens.
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