川东獐牙菜(龙胆科)的胚胎学研究

Embryology of Swertia davidii(Gentianaceae)

关键词:  川东獐牙菜  胚胎学  獐牙菜属

Key words:  Swertia davidii  embryology  Swertia

摘要:

利用石蜡切片技术,对川东獐牙菜(Swertia davidii)的胚胎发育过程进行显微观察,并根据现有资料,对獐牙菜属的几种植物进行了比较胚胎学研究。结果表明:川东獐牙菜花药四室,药壁发育为基本型,绒毡层异型起源,为腺质绒毡层,发育后期药室内观察到的绒毡层核是早期该层细胞有丝分裂凸入药室并原位退化形成的,中层细胞3层,药室内壁退化,花药壁表皮宿存,细胞柱状伸长,纤维状加厚; 小孢母细胞减数分裂为同时型,四分体排列方式主要为四面体形和左右对称型,少数为“T”形和十字交叉形,成熟花粉为2-细胞类型; 子房2心皮、1室,侧膜胎座; 薄珠心,单珠被,倒弯生胚珠,大孢子母细胞减数分裂形成4个大孢子直线形排列,合点端的大孢子具功能,雄配子体发育为蓼型; 2个极核在受精前融合为1次生核,合点端3个反足细胞宿存,每个细胞均多核和异常膨大,形成明显的反足吸器,并在胚乳之外形成染色较深的类似“外胚乳”结构; 珠孔受精,受精作用属于有丝分裂前类型; 胚乳发育为核型,胚胎发育为茄型; 果实成熟时,种子发育至心形胚阶段; 反足细胞在龙胆科一些短命植物中的宿存与分裂具有重要的生殖适应与进化意义。

Abstract:

The study includes the development of microsporangium,male gametophy,megasporogenesis,female gametophyte and embryogeny of Swertia davidii. The main results were as follows: anthers were tetrasporangiate. The development of anther walls conforms to the basic type and comprises of epidermis, endothecium, three middle layers and tapetum at the mature stage. The tapetum cells had dual origins and belonged to the glandular type, for the anther locules had degenerating tapetum nuclei in the middle,which were from the early dividing and intruding of the tapetum. Three middle layers were ephemeral,endothecium reduced and epidermis persists and developed to become fibrous-thickening. The cytokinesis of the microspore mother cell in meiosis was the Simultaneous type. Most of the microspore tetrads were tetrahedral and there were still a few other types,such as isobilateral,dilateral and “T”-shaped. Pollen grains were 2-celled when shed. The ovary was bicarpellate,unilocular with some series of ovules located at the parietal placentation. The ovule was unitegmic,enuinucellar and ana-campylotropous. The female gametophyte originated from the single-archesporial cell. The one chalazal megaspore in linear tetrad became the functional megaspore. The development of female gametophyte was the polygonum type. Before fertilization,two polar nuclei fused into a secondary nucleus. Three antipodal cells had multiseriate nuclei and distinct haustorium,and persisted like a layer of “outer endosperm” just out of the endosperm nucleus layer. Fertilization was porogamous and of premitotic syngamy type. The development of endosperm conformed to nuclear type and the embryogeny corresponded to the solanum type. The embryo was at the early heart-shaped stage when seeds released from the capsule. The dividing and persisting of the antipodal cells in some annual Gentianaceous plants were of significance in reproductive adaptation and evolution. At the same time,comparative embryology among some species of Swertia was studied basing on some recent data.