| 1. The meiosis of pollen mother cells and the development of the male gametophytes were studied by chromosome preparation staining technique. The results obtained included: (1) External characters of male flower was closely related to the meiosis of the pollen mother cells, which can be used as the material-selecting basis of cell molecular and microspore culture; There were two to four division phases simultaneously observed in the same plate and same flower bud and even in same anther, which indicate the meiosis asynchronization; (2) The separated lagging chromosomes were found at anaphaseⅠ, which show the genetic heterogeneity, spindle arranged in vertical, parallel in metaphaseⅡ, the microspores in tetrad stage showed the arrangement of decussate type, tetrahedral type and isobilateral type, and cytoplasms were divided simultaneously; (3) In the development process of the male gametophytes, uninucleate stage account for longer time. Mature pollen grains were tricellular.2. The diploid non-heading Chinese cabbage (2n=2x=20) with spontaneous 2n gamete was usedto study the mechanism of forming unreduced gamete (n=2x=20) by traditional squash method. In our meiotic study of microspore mother cells (MMCs), it was found that the first meiotic division and cytokinesis were both normal, but there are abnormal orientations (parallel spindle, tripolar spindle) at the second meiotic division, and dyads and triads were found at the tretrad stage, which lead to the formation of 2n pollen. The formation of 2n gamete due to spindle orientation abnormality is equivalent to FDR genetically, which have important utilization value in the sexual polyploidization breeding.3. The diploid non-heading Chinese cabbage (2n=2x=20) which can naturally produce 2n female gamete was used to study female meiosis and the mechanism of forming unreduced gamete (n=2x=20) by squash method for the first time. It show that female meiosis was successive, that is, dyads were formed after the first meiosis, followed by the second one. It was found that the first meiotic division and cytokinesis were both normal, but there were abnormalities at the second meiotic division. At the tretrad stage, it turns out various patterns:triads with one 2n gamete and dyads with two 2n gametes; linear tretrads and pentads with n gamete; T-typed tretrads. The formation of 2n female gamete is equivalent to SDR (the second division restitution) genetically. After the meiosis, functional megaspore gradually develop mononuclear embryo sac, binuclear embryo sac, tretanuclear embryo sac, octanuclear embryo sac,finally, mature embryo sac.4. In this article, we studied diploid non-heading chinese cabbage karyotype analysis using immature pistil via conventional pressed slice methed. The results indicated that:the immature gynoecium possessed more cells which were at metaphase stage. The karyotype formula was 2n=2x=20=14m+2sm+4st (2SAT), with 7 metacentric pairs (1,2,3,4,7,8,9), 1 acrocentric pairs (6) chromosomes, and 2 (5,10)nearly terminal pairs, satellites were observed at the tenth pair of chromosomes. The variation rage of relative length is 0.62-1.42, the length formula was 2n= 1L+5M1+2M2+2S. The karyotype belongs to 2B.5. The diploid non-heading Chinese cabbage (2n=2x=20) treated by colchicine was used to study the cytological mechanism of 2n female and 2n male gamete. After observed and analyzed by traditional squash method, it showed that there were some abnormalities of the induction of 2n male gamete at the meiosis, such as the formation of chromosome bridge, ring chromosome, failure of synapsis and cytokinesis. Finally, it turn out to be dyad, triad and a few aneuploidy. During the meiosis of the induction of 2n female gamete it was found that asynapsis and abnormal cytokinesis result in dyad, monads with binuclear. Therefore, the formation of 2n gamete induced by colchicine in non-heading Chinese cabbage is due to FDR (the first division restitution) and SDR(the second division restitution). |
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