紫纹兜兰的花形态和双雄蕊花药发育及分类学意义

Floral morphology and anther development in diandrous orchid Paphiopedilum purpuratum with their taxonomic implications

关键词:  兜兰属, 杓兰亚科, 花药壁发育, 小孢子发生, 雄配子体发育, 花粉散粉单元, 分类学

Key words:  Paphiopedilum, Cypripedioideae, anther wall development, microsporogenesis, male gametogenesis, pollen dispersal unit, taxonomy

摘要:

兜兰属的分类系统学争议较大,亟待更多资料澄清。该文利用体式解剖镜和石蜡切片技术观察了紫纹兜兰的花结构和双雄蕊花药发育特征。结果表明:(1)花形态特征支持将紫纹兜兰放置于兜兰亚属的单花斑叶组,包括萼片具脉纹、花瓣长圆形带黑褐斑,唇瓣具直立的耳状结构,退化雄蕊新月形等。(2)花药原基分化出一对侧生并列的药室,花药室中央分化出一条不完全贯穿的不育隔膜组织,将其分化为两个小孢子囊。在花药成熟时,不育隔膜组织被降解吸收,两个花粉囊通过次生融合形成一枚马鞍形的黏性花粉团。(3)发育完整的花药壁有4层,由外到内分别为表皮、药室内壁、中层和绒毡层,符合单子叶型花药壁。花药壁具绒毡层和内绒毡层,均为2核。在2-细胞花粉时期,中层和绒毡层发生降解,药室内壁发生纤维状加厚。(4)小孢子母细胞经同时型胞质分裂形成不同排列方式的小孢子四分体,包括正四面体、左右对称和十字交叉型,并且同一药室的小孢子母细胞减数分裂不同步现象明显。(5)在雄配子体发育阶段,小孢子或保持在四分体内或从四分体中游离出来,经有丝分裂发育为2-细胞型花粉,形成具有黏性的四合花粉或花粉粒。基于现有资料,该文比较分析了紫纹兜兰不完全贯穿的不育隔膜组织、单子叶型花药壁、具2核的绒毡层和内绒毡层、同时型胞质分裂和黏性花药等特征的分类学意义,为理解兜兰属及杓兰亚科的分类学和保护生物学提供新资料。

Abstract:

The taxonomy of Paphiopedilum Pfitz. has been disputed and needs more data for clarification. Floral morphology and anther development in P. purpuratum were observed using microscope and paraffin section. The results were as follows:(1)It was supported that P. purpuratum should be placed in Paphiopedilum subgenus Paphiopedilum sect. Barbata by some floral features, including a single flower, sepal white with veins, petal spotted with blackish-maroon, pouch of a lip auriculate on both sides, and a staminode lunate.(2)At the early stage, anther primordium developed into a pair of laterally juxtaposed thecae. An incomplete sterile septa was differentiated in the center of each theca, giving rise to two arc-shaped microsporangia. When anther split, the sterile septum was discomposed and degenerated resulting in a mass of sticky pollens from two pollen sacs were fused into a unit.(3)The developed anther wall consisted of an epidermis, an endothecium, a middle layer, and a tapetum, conforming to the monocotyledonous type. Both tapetum and the inner tapetum cells contained 2 nuclei. At the stage of 2-celled grains, degeneration occurred in the epidermis and tapetum layers, while the endothecium became thickened fibrously.(4)Microspore mother cells underwent a simultaneous cytokinesis resulting in microspore tetrads with varied arrangements of tetrahedral, isobilateral, and decussate types, and the meiotic activity of microspore mother cells in the same theca was obviously asynchronous and different meiosis phases could be observed.(5)Microspores produced 2-celled pollens via a mitosis, which could be retained in pollen tetrads or released as monad. Based on the data available, some key features are selected for taxonomy and conservation biology of Paphiopedilum in Cypripedioideae, including the differentiation of incomplete sterile septum, the monocotyledonous type of anther wall, the binucleated tapetum, differentiation of the inner tapetum, simultaneous cytokinesis, the sticky pollens, and so on. This study provides new information for taxonomy and conservation biology of Paphiopedilum, as well as of Cypripedioideae.