Abstract: [Objective] This study was aimed to observe the meiosis of pollen mother cell and the karyotype of Carya cathayensis, to determine the chromosome number and ploidy level of C. cathayensis according to these results, to explore the relationship between the apomixis and the ploidy level of C. cathayensis, and to enrich reproductive biology data of Carya species, meanwhile, to provide some cytological data for cross breeding and systematic classification of C. cathayensis.[Method] 1)Male inflorescence of C. cathayensis was selected as material, DAPI fluorescent staining was used to study the meiosis of pollen mother cell of C. cathayensis. 2) C. cathayensis root tip was selected to prepare chromosome and make karyotype analysis.[Result] 1)The meiosis of pollen mother cells of C. cathayensis was divided into two stages, the chromosome number of daughter cells was reduced by half during the first division and not changed again during the second division. The first and second division were divided into prophase, metaphase, anaphase and telophase respectively, however, the prophaseⅠwas most complex among these stages and was further divided into leptotene, zygotene, pachytene, diplotene and diakinesis. The prophaseⅠwas the longest one among these stages, accounting for nearly 70% of the whole division cycle. The second division was relatively a shorter period. 2) In terms of meiosis synchronization, different anthers from the same floret are the same, there was no significant difference among different flowers from the same inflorescence axis. 3)The chromosome behavior of most pollen mother cells in C. cathayensis was normal and paired as 16 bivalents at metaphaseⅠ. However, there was a certain proportion of abnormal pollen mother cells in the meiosis, such as appearing lagging chromosome in metaphase Ⅰ, which accounted for 8.86%, showing asymmetry division in metaphase Ⅱ, which accounted for 15.79%. 4) The karyotype formula of C. cathayensis was 2n=32=20m+12sm,and the range of its chromosome relative length was from 4.006(±0.449) to 9.559(±1.175), chromosome numbers whose arm ratio was more than 2 accounted for 25.000%, the ratio of chromosome length (L/S) and the karyotype asymmetry index were 2.417±0.456 and 62.875, respectively. The karyotype type was 2B.[Conclusion] 1) Although there is the phenomenon of apomixis in C. cathayensis, it still follows the law of meiosis of pollen mother cells in most angiosperms. In the whole process of meiosis, the prophase Ⅰ is the longest, other stages are short. 2) C. cathyensis pollen mother cell meiosis synchronization degree is very high, which is unfavorable to prolong its pollination period. 3) The abnormal mother cell of C. cathyensis mainly appears in the two stages of metaphase Ⅰ and metaphase Ⅱ. 4) The karyotype of C. cathyensis belongs to a symmetrical type with the chromosome number of 2n=32 and paired as 16 bivalents at meiosis metaphaseⅠ, thus it is a diploid species.

Key words: Carya cathayensis, meiosis, pollen mother cell, chromosome, karyotype, apomixis