天山蒲公英两种生殖方式个体的性细胞分化

Differentiation of Sex Cells in the Two Reproductive Ways of Taraxacum tianschanicum

天山蒲公英(Taraxacum tianschanicum)具有有性和无融合两种生殖方式,为了解两种生殖方式个体的性细胞分化的异同点,本研究采用常规石蜡切片法,对天山蒲公英两种生殖方式个体的大、小孢子发生及雌、雄配子体分化进行了对比观察。结果表明,无融合生殖个体与有性生殖个体的小孢子分化阶段无明显区别,四分体分化期之后,两性生殖个体的雄配子体依次分化形成单核、二核、三核花粉,而无融合生殖个体进入了雄配子体败育期;与两性生殖个体的大孢子和雌配子体分化过程相比,无融合生殖个体的大孢子母细胞不经过四分体分化期,二分体的合点端大孢子发育成胚囊,卵细胞不通过受精作用就发育成心形胚。无融合生殖个体雄配子体败育可能是胼胝质不分解或绒毡层结构发生异常所致;兼性无融合生殖特性的出现可能是该植物适应多变气候特征的进化对策。本研究可为蒲公英植物的分类和植物无融合生殖发生机理提供胚胎学参考依据。

Taraxacum tianschanicum has both sexual and apomixis reproductive methods.To understand the differences and similarities of sexual cell differentiation in the two reproductive ways.In this study,the megasporogenesis,microsporogenesis and the differentiation of female and male gametophytes of the two reproductive ways of T.tianschanicum were observed and compared using routine paraffin section technique.The results showed that the differentiation of microsporocyte of the apomixis individuals were not significantly different from those of the sexual individuals.After the occurrence period of tetrad,the male gametophytes of the sexual individuals were divided into single-core,two-core and three-core pollen period in order,while the apomixis individuals entered the male gametophyte abortion period;Compared with megasporogenesis and differentiation of female gametophytes in sexual individuals.The megaspore mother cells of the apomixis individuals without having passed through the tetrad.The chalazal megaspore of the diad develops into the embryo sac,and the egg cells developed into cardiac embryos without fertilization.The abortion mode of male gametophyte in apomixis individuals may be caused by the failure of decomposition of callose or abnormal decomposition of tapetum,and the appearance of facultative apomixis characteristics may be the evolutionary adaptation strategy of the plant to the changing climate.This study can provide embryological reference for the classification of Taraxacum and the mechanism of plant apomixis.