分类： 生物学 >> 植物学 提交时间： 2017-07-13
摘要： Premise of research. Comparative development of staminate and pistillate flowers of Pseuduvaria trimera (Annonaceae) is firstly investigated to understand its sexual differentiation and developmental processes of flowers. Comparisons of morphological and anatomical features between mature stamens and staminodes are also described, in order to clarify the mode of anther dehiscence and understand the mechanism underlying the sterility of the staminodes. Methodology. Flowers at different developmental stages and mature stamens and staminodes were examined with SEM and light microscopy. Pivotal results. Flowers have complex whorled phyllotaxis as in other Annonaceae, with double positions in the outmost whorl of reproductive organs and variable stamen and carpel organ numbers per whorl. The stomium region of each theca is composed of the septum and stomium. The septum and stomium cells of stamens could be degenerated developmentally, facilitating anther opening, whereas those of staminodes maintain intact, forming indehiscent anthers. Conclusions. The developmental data suggest that staminate flower is unisexual from inception, while pistillate flower is morphologically hermaphroditic. The morphologically hermaphroditic flowers are nevertheless functionally pistillate as the anthers are indehiscent, and the structural andromonoecy of P. trimera actually functions as monoecy. The mechanism underlying the sterility of the indehiscent staminodes and delayed dehiscent outer stamens might be effective in promoting xenogamy. The occurrence of staminode is closely correlated with the acquisition and evolution of functional unisexual flowers in the genus Pseuduvaria.
分类： 生物学 >> 植物学 提交时间： 2017-07-12
摘要： Species of Myristicaceae have diverse and distinctive synandria morphology and structure, making them an interesting group for androecium evolution research. To clarify the morphology, structure, and origin of the synandrium, scanning electron microscopy and histology were performed on staminate inflorescences and flowers of Horsfieldia pandurifolia, H. tetratepala, and Myristica fragrans at different developmental stages. A whorl of stamen primordia was initiated rapidly around the margin of the floral apex in groups of two in H. pandurifolia and groups of three in M. fragrans. Each stamen primordium grew longitudinally, producing a pair of anther lobes and four microsporangia, accompanying one vascular bundle in H. pandurifolia and M. fragrans. In H. tetratepala, three stamen primordia groups were formed and each group with several anthers was supported by one vascular bundle, indicating a secondary increase of stamen. Three types of synandria origins were observed—in M. fragrans, the central sterile column tissues originated from the elongate receptacle; in H. pandurifolia and H. tetratepala, they were derived from a combination of floral meristem and fused connectives, and a combination of receptacular tissue and stamen groups. The diverse origins of the central sterile column suggest that the synandrium develops differently and independently in different genera and species of Myristicaceae.
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