毛钩藤的小孢子发生和雄配子体发育

Microsporogenesis and Male Gametophyte Development in Uncaria hirsuta Havil. (Rubiaceae)

摘要:

在光学显微镜和透射电镜下观察了毛钩藤(Uncaria hirsuta Havil.)的小孢子发生和雄配子体发育过程。结果表明，毛钩藤花两性，具5枚雄蕊，花药4室，花药壁由表皮、药室内壁、中层和绒毡层组成，花药开裂时，药室内壁高度纤维化带状加厚。花药壁的发育方式属于双子叶型，小孢子母细胞减数分裂的胞质分裂为同时型。小孢子在四分体时期开始沉积花粉外壁，小孢子大液泡化时期开始沉积花粉内壁。成熟花粉为2-细胞型。毛钩藤的花粉发育特征和茜草科植物基本一致。毛钩藤绒毡层属于分泌型，双重起源，分别起源于次生周缘层和药隔细胞。小孢子发育早期绒毡层开始降解并分泌形成大量乌氏体，花药开裂时绒毡层完全消失，剩下少量乌氏体。小孢子早期内壁加厚突出形成，小孢子细胞核分裂以后内壁加厚开始脱落，花药开裂时，只剩下少量的内壁加厚突出。初步推测，内壁加厚突出与乌氏体共同作用为雄配子体的发育提供营养物质。

Abstract:

Microsporogenesis and male gametophyte development of Uncaria hirsuta Havil. (Rubiaceae) were studied under light microscopy (LM) and transmissiom electron microscopy (TEM). Flowers of U. hirsuta are monoclinous, which each have five stamens, and the anther is tetralocular. The anther wall is composed of epidermis, endothecium, middle layer(s) and tapetum, the endothecium becomes fibrously thickened at anther dehiscence. The development of the anther wall is the dicotyledonous type, the cytokinesis following meiosis is simultaneous, producing tetrahedral tatrads and rarely isobilateral ones. The exine deposition is initiated during the tetrad stage, and the intine formation begins at vacuolated microspore stage. Mature pollen grains are two-cell type. The ontogenetic features of microsporogenesis and male gametophyte development in U. hirsuta basically follow the pattern of Rubiaceae. The tapetum is secretory type, and dual ontogeny, originating from the parietal layers and connective-derived layer, respectively. Tapetum begins to degenerate at the early stage of free microspore, producing lots of ubisch bodies, and it becomes completely degenerated at anther dehiscence. Protruding onci occur at uninucleate microspore stage, most of which shed during binucleate microspore stage. It is preliminarily presumed that the protruding onci might play an important role in pollen development.