Chromosome Karyotype Analysis On Five Species Of Taxodiaceae

Taxodiaceae is not a numerous family in Gymnospermae. Because of its straight texture, detailed structure, soft texture, anti-corrosion, less plant disease and rapid growth, Taxodiaceae become one of important species in China for its plantation, landscape forest and water-protected forest.The five species of Taxodiaceae are C. lanceolata, C. fortune, C. japonica, T. ascendens and T. distichum. Karyotype formulas and the karyotype classification of the five species were established in this study. The analysis of chromosomes were made using AI Cytovision and Image Pro Plus6.0. Preliminary karyotype, genetic relationship and evolutional trend on the five species of Taxodiaceae were compared in this study. The main results were as follows:1. The number of metaphase of apical organization had little difference in two different time periods at8:00-10:00am and at3:00-5:00pm.2. Basing on the existing plant chromosome karyotype analysis methods, we have improved the methods of karyotype analysis and explored a karyotype analysis method for Taxodiaceae. Use of seed germination to root, do not cut root tip until root length to0.5-1cm; Tender tissues were pretreated with0.2%colchicine:0.002mol/L8-hydroxyl quinoline=1:1mixture for6-8h; Use freshly prepared Carnoy’s Ⅰ(alcohol:acetic=3:1) to fixed the root for20-24h; Disintegrated the root in lmol/L HCL solution for6-10min in60℃water bath; Stained with modified phenol magenta, Tabletting, microscopic examination. The arrangements of chromosomes and pairing were made using of AI Cytovision and Image Pro Plus6.0.3. The chromosome number of these five species are all22, they are all diploid. The five plants were mainly made up of the metacentric chromosome and submetacentric chromosome, which were symmetrical and of a primitive type. The karyotype formula of C. lanceolata was:2n=2x=22=20m (2SAT)+2sm, The karyotype classification of C. lanceolata was:"2B", No.4chromosome was found the satellite. The karyotype formula of C. fortune was:2n=2x=22=20m+2sm, The karyotype classification of C. fortune was:"2A", No.11chromosome is submetacentric chromosome. The karyotype formula of C. japonica was:2n=2x=22=20m+2sm, The karyotype classification of C. japonica was:"2A", No.9chromosome is submetacentric chromosome. The karyotype formula of T. ascendens was:2n=2x=22=20m, The karyotype classification of T. ascendens was:"1A", all the chromosomes are metacentric chromosomes. The karyotype formula of T. distichum was:2n=2x=22=20m, The karyotype classification of T. distichum was:"1A", all the chromosomes are metacentric chromosomes.4. Compare the karyotype of the five species of Taxodiaceae, we can get that C. fortune and C. japonica had closer relationship, T. ascendens and T. distichum had similar origin. The five species can be divided into three categories:C. lanceolata is for a class, C. fortune and C. japonica are for a class, T. ascendens and T. distichum are for a class.5. According to the scatter diagram, which based on the degree of karyotypic asymmetry of Taxodiaceae, C. lanceolata is evolutionary, C. fortune and C. japonica are more primitive, T. ascendens and T. distichum are most primitive. The order of karyotype symmetry of the five species is:T. distichum> T. ascendens> C. japonica> C. fortune> C lanceolata. The evolutional trend of the five species is:C. lanceolata> C. fortune> C. japonica> T. ascendens> T. distichum.