中国特有种苦绳(广义夹竹桃科)的大小孢子发生和雌雄配子体发育及其分类学意义

Sporogenesis and gametogenesis in Chinese endemic plant of Dregea sinensis var. sinensis(Apocynaceae sensu lato)and their taxonomic insights

关键词:  广义夹竹桃科, 苦绳, 大小孢子发生, 雌雄配子体发育, 分类学意义

Key words:  Apocynaceae sensu lato, Dregea sinensis var. sinensis, sporogenesis, gametogenesis, taxonomic significance

摘要:

近年来的分子系统学把狭义萝藦科和狭义夹竹桃科合并为广义夹竹桃科,包括5个亚科和25个族,但亚科和族间的亲缘关系较为复杂,亟待多学科证据澄清。本文利用常规石蜡切片技术观察了马利筋亚科南山藤属中的中国特有植物苦绳(Dregea sinensis var. sinensis)的孢子发生和配子体发育,结合已有资料比较了5个亚科的胚胎学特征。结果表明:(1)苦绳的花药由一对侧生并列药室组成,各有一个花粉团。(2)花药壁有6层,由外至内分别为表皮、2层药室内壁、中层和2层绒毡层,花药壁发育模式属于多层型。(3)绒毡层细胞单核,排成2列,为腺质型; 在小孢子四分体形成时期,药室内壁发生明显纤维状加厚; 花药成熟时,位于药室远轴最外侧处的花药壁发生断裂,准备散粉。(4)小孢子母细胞减数分裂中,胞质分裂方式为连续型,小孢子四分体排列方式为左右对称; 成熟花粉粒为3-细胞型,排列紧密,形成花粉团。(5)雌蕊含有两枚离生心皮,具边缘胎座,胚珠倒生,单珠被,薄珠心,蓼型胚囊。本文观察到的这些胚胎学特征为牛奶菜族提供了新资料。同时,胚胎学特征在5个亚科间的区别和联系,支持广义夹竹桃科的成立。

Abstract:

Asclepiadaceae s. str. and Apocynaceae s. str. have been combined as a monotypic family of Apocynaceae s. l. based on molecular data, including 5 subfamilies and 25 tribes. However, the relationships between subfamilies and tribes are complicated and needed to be further clarified. Sporogenesis and gametogenesis in Chinese endemic plant of Dregea sinensis var. sinensis(trib. Marsdenieae, subfam. Asclepiadoideae)were investigated using paraffin sectioning, and then the observed embryological characters were compared with those of five subfamilies for taxonomic insights. The results were as follows:(1)The anther was comprised of two lateral thecae containing a pair of pollinia.(2)The developed anther wall consisted of six layers, including an epidermis, two layers of endothecium, a middle layer, and 2-layered tapetum. So, the anther wall development was of Massive type.(3)The tapetum was uni-nucleated,2-layered, and of glandular type. Endothecium developed fibrous thickenings heavily and a slit occurred at abaxial position of each theca when anther was ripened.(4)The microspore mother cells underwent meiosis with a successive cytokinesis and produced microspore tetrads with isobilateral arrangement. The microspores retained in tetrads developed into 3-celled pollens by mitosis twice, which formed a compact pollinium.(5)The pistil was composed of two separate carpels containing many anatropous, tenuinucellar, and unitegmic ovules with marginal parietal placentations. The development of embryo sac conformed to the Polygonum type. These embryological features observed added new data to the tribe Marsdenieae. It was confirmed that the recognition of a monophyletic Apocynaceae s. l. was supported by some distinguished and related embryological characters among five subfamilies.