高粱A_6型细胞质雄性不育系花粉母细胞减数分裂行为的观察和分析

高粱(Sorghum bicolor L.Moench)细胞质雄性不育(CMS)有7种类型,即A1～A6和9E。本研究以A6型细胞质雄性不育系A6Tx398和相应保持系B6Tx398为材料,对A6型雄性不育发生的花粉母细胞减数分裂过程染色体行为进行了观察分析。与正常发育的保持系比较,A6CMS花粉母细胞减数分裂染色体行为,在粗线期之前,光学生物显微镜下未观察到差别。从双线期开始,直到末期II观察到各种各样的异常现象。即A6CMS花粉母细胞染色体数目比B6(2n=20)多一倍,前期I染色体数目为2n=40,在一个细胞中可看到20对同源染色体;后期I同源染色体在移向两极时出现染色体滞后和暂时不分离现象;花粉母细胞末期I未发生胞质分裂形成二分体,致使在前期II可看到有40条姊妹染色体,并以环形、分散形和X型分散于一个细胞中;末期II,在一个细胞内形成2个、3个或4个数目不等的染色体团,个别的可以形成染色体数目不等的三分体,而不形成四分体。A6型CMS花粉母细胞减数分裂过程中染色体行为的异常,使其不能完成正常的减数分裂过程形成四分体,导致小孢子败育。

Observation and Analysis of Meiotic Behaviors of Pollen-Mother-Cell in Sorghum A_6 Cytoplasmic Male Sterile Line

Sorghum (Sorghum bicolor L. Moench) is one of the most important food crops in the world, and it is also one of the earliest crops, which the heterosis has been commercially used due to the discovery and utilization of cytoplasmic sterility (CMS). There are seven types of CMS in sorghum, including A₁, A₂, A₃, A₄, A₅, A₆, and 9E. In this study, A₆ cytplasmic male sterile line A₆ Tx398 and its isogonic maintainer line B₆ Tx398 were used to observe and analyze the chromosomal behaviors of A₆ CMS during the microsporic meiosis. Compared with maintainer line B₆ Tx398, the abnormal chromosomal behaviors were not observed under biologic photomicroscope until the diplotene in prophase I. From then on to the tetrad formation, various abnormal chromosomal behaviors were found within the pollen mother cells (PMCs): compared with its B₆ line in most of the PMCs in prophase I, the number of homologous chromosomes was twice (2n=40) that of its isogenic line (2n=20), i.e. 20 pairs of homologs in a cell. In anaphase I, some homologs became lagged or even not divided and stayed near the equatorial plane. Cytoplasm of most PMCs did not divide to form a dyad in telophase II, so that in prophase II 40 sister chromosomes presented in a cell, which were arranged ring-like,  dispersed or X-like. In telophase II, two, three or four chromosomal groups were found in a cell. Some PMCs divided into triad other than tetrad with unequal number of chromosomes in each monad. The disorders of chromosomal behaviors during the pollen mother cell meiosis of A₆ CMS made the incompletion of the normal meiotic process, leading to the abortion of microsporogenesis and development.