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.