华北落叶松小孢子母细胞(PMC)减数分裂和花粉的发育

采用染色体压片法系统地观察了华北落叶松Larix principis-rupprechtii小孢子母细胞(PMC)减数分裂的细胞学特征和花粉发育过程。结果表明:华北落叶松PMC减数分裂始于当年秋季,以弥散双线期的特殊状态休眠越冬,次年春天又重新恢复其后续的减数分裂过程。主要特点是在同一花药中,减数分裂不同步,且各阶段分裂速度较快,3天内全部停留在四分体阶段;二价体构型主要为两臂共发生过两次以上交换的环形二价体,少数细胞中偶见一臂发生交换的棒状二价体;其平均构型为10.62II 1.38II;中期II核分裂相既有平行式样,又有互为垂直式样,形成左右对称型和四面体型四分体,兼具单、双子叶植物四分体主要类型特点。四分体持续一周后,细胞壁开始溶解,4个小孢子分离并游离在药室中,成为独立的单核花粉。其后细胞核开始有丝分裂,最后形成由2个原叶细胞、1个管细胞、1个柄细胞和1个体细胞共5个细胞组成的成熟花粉。此外,还观察到成熟花粉当中有13.6%是由4个细胞组成的。

Studies on the pollen mother cell meiosis and pollen development of Larix principis-rupprechtii

Using the squash method for chromosomes, cytological characters in pollen mother cells (PMC) and pollen development traits of Larix principis-rupprechtii were investigated. Our results showed that the PMC meiosis of L. principis-rupprechtii began in autumn, remained at the diffuse diplotene stage through the dormancy of the plant during winter and re-started the next spring to complete the process. It is mainly characterized by the lack of synchronization of meiosis in the same anther and by the relatively quick processes of every meiosis stage. After the re-start of meiosis, all the PMCs reached the tetrad stage within three days. The main configuration of bivalents were rings caused by more than two chromosome exchanges on the arms. Rod-bivalents produced by chromosome exchange on only one arm were rarely observed in a few cells. The average configuration was 10.62II 1.38I. Of meiosis Metaphase II, there were patterns of parallel or perpendicularity, forming eudipleural or tetrahedral tetrads, which are also the major tetrad types in the monocots and dicots. After one week at the tetrad stage, callose cell walls started to dissolve, then the four cells separated, and dispersed into the pollen cell, forming independent single-nucleus pollen grains. Afterwards, the haploid nucleolus underwent further cycles of mitotic division, resulting in the formation of five-celled pollen with two prothallial cells, one tube cell, one stalk cell and one body cell.