珍稀濒危植物大花万代兰的花粉团发育及其分类学意义

Pollinia Development in Rare Orchid of Vanda coerulea with Its Taxonomic Implications

万代兰属的属间界限划定及其亲缘关系重建是兰科分类系统中的难解之谜。该研究采用常规石蜡切片技术观察了珍稀濒危植物大花万代兰的一对深裂花粉团的形成机制、花药壁发育模式、小孢子发生及雄配子体发育等的胚胎学特征。结果表明:(1)大花万代兰早期的花药原基分化出一对侧生药室,每个药室的小孢子囊中央分化出一条在花药成熟时会降解的不育隔膜组织,形成两个不等深裂的花粉团。(2)发育完整的花药壁有5~9层,包括2~6层药室内壁,符合多层型花药壁发育类型;绒毡层细胞为单核,腺质型,在花药成熟时,表皮、中层和绒毡层皆降解,仅留下2~6层纤维性加厚的药室内壁。(3)小孢子母细胞经过连续型胞质分裂形成正四面体和左右对称的小孢子四分体,小孢子四分体继续保持在同一个胼胝质内,完成有丝分裂形成了2-细胞型的四合花粉;四合花粉两两紧密排列,且由于隔膜组织的降解,最终发育为一对深裂的花粉团。根据现有兰花花药发育资料,分析了大花万代兰花粉团发育的胚胎学特征的分类学意义,为万代兰属错综复杂的系统分类提供了新资料。

We investigated pollinia development in rare orchid Vanda coerulea using paraffin sectioning in order to provide some embryological data to clarify the generic delimitation of Aerides-Vanda alliance. Results are as follows:(1) initially anther primordia were differentiated into a pair of thecae containing two microsporangia. And then, a sterile septum was formed longitudinally and unequally in each microsporangium during microsporogenesis. Finally, the septum was totally absorbed leading to 2 cleft-pollinia at ripen anther stage.(2) The development of anther wall was of massive type due to 5-9 layers including a transient epidermis, 2-6 endothecium layers, a middle layer and a uninucleated tapetum.(3) Microspore mother cells underwent a successive cytokeinsis during meiosis resulting in some tetrahedral or isobilateral microspore tetrads. Microspores retained in tetrads and developed into 2-celled pollen tetrads. The pollen tetrads arranged compactly within the collapsed anther wall and formed 2 cleft-pollinia in anther. These embryological features provided new data to the taxonomy of Vanda S. S.