云南火焰兰的花形态和花药发育的胚胎学特征

Floral morphology and embryological features of anther development in Renanthera imschootiana

关键词:  火焰兰属, 形态学, 花粉团发育, 多层型花药壁, 小孢子发生, 雄配子体发育

Key words:  Renanthera, morphology, pollinium development, anther wall of massive tape, microsporogenesis, male gametophyte development

摘要:

关于珍稀濒危植物火焰兰属的研究资料较少。该文以云南火焰兰为研究对象,通过显微镜和石蜡切片技术观察了云南火焰兰的花形态和花药发育胚胎学特征,并结合现有资料探讨了其分类学意义。结果表明:(1)具有分类学意义的花形态特征为唇瓣三裂且花距不明显,合蕊柱圆柱形,花药帽紫色具黄条纹,花粉团一对且由粘盘及粘盘柄连接。(2)花药原基分化出一对侧生花药室,每个花药室的小孢子囊中央分化出一条偏离中轴的不育隔膜组织,发育为一对不等大的次生小孢子囊; 花药成熟时,因不育隔膜组织降解而形成2个深裂花粉团。(3)发育完整的花药壁有5～6层,为“多层型”花药壁,包括表皮、2～3层药室内壁、中层和绒毡层; 绒毡层细胞为单核、腺质型。花药成熟时,药室内壁发生纤维状加厚,花药室在远轴端开裂散粉。(4)小孢子母细胞经同时型胞质分裂,形成正四面体和左右对称排列的小孢子四分体,小孢子保持在四分体内,经有丝分裂发育为2-细胞型的四合花粉,排列紧密,形成坚固的花粉团; 在花药发育过程中未观察到花粉败育现象。该研究结果为火焰兰属的分类学和保护生物学提供了新资料。

Abstract:

There are few data on the rare and endangered orchids of Renanthera Lour. Floral morphology and embryological features of anther development in R. imschootiana were investigated, and the taxonomic significance of R. imschootiana was analyzed by comparing with existing data. The results were as follows:(1)Flowers were characterized by such taxonomic features as tri-lobed labium with an unconspicous spur, cylindrical column, purple anther cap with yellow stripes, and a pair of deeply cleft pollinia connected by a well-developed stipe and a viscidium.(2)Anther primordium was differentiated into two lateral thecae containing two densely dyed microsporangia, and then, a sterile septum was formed longitudinally and unequally which divided each microsporangium into two jointly sub-microsporangium. The septum became absorbed during microsporogenesis and collapsed when anther ripened, resulting in a pair of deeply cleft pollinia.(3)The developed anther wall comprised 5-6 layers, including an epidermis, 2-3 endothecium, a middle layer, and a tapetum, which conformed to the massive type. Tapetal cell was uni-nucleated and glandular.(4)Microspore mother cells underwent a simultaneous cytokinesis during meiosis resulting in the tetrahedral or isobilateral microspore tetrads. Finally, each microspore retained in tetrads and produced 2-celled pollen via mitosis. Pollen tetrads were compactly arranged, leading to a hard cleft pollinia in each thecae. No pollen abortion was observed during anther development. The results provide new reference for taxonomy and conservation of Renanthera.