Studies On The Chromosome Evolution And Nuclear DNA Content Of Saussurea Subg.Eriocoryne And Subg.Amphilaena

Saussurea Subg.Eriocoryne and Subg.Amphilaena belong to Saussurea.Saussurea has about 80 species,of which 73 species are distributed in China,and 50species are endemic to China.The species are mainly distributed in extreme environments at high altitudes on the Qinghai-Tibet Plateau,and fiercely differentiated.They are the ideal taxa for studying the evolution and adaptation mechanisms of species in alpine regions,and also the good materials for the evolution ecology research.At present,there are few studies on the karyotypes in the Qinghai-Tibet Plateau.In this study,8 species of 12 Subg.Eriocoryne and Subg.Amphilaena collected from the Qinghai-Tibet Plateau was performed on karyotype research,and to further analyze the chromosomal evolution trend of two subgenus.To use flow cytometry(FCM)collected the nuclear DNA content(2C)of Subg.Eriocoryne and Subg.Amphilaena from 17species and 68 populations in the Qinghai-Tibet Plateau.The main results are as follows:The karyotype study of Subg.Eriocoryne and Subg.Amphilaena showed that:(1)The chromosome bases of the two subgenus are x=13,x=14,x=15,x=16,x=17.Ploidy of the two subgenus is mainly diploid.The evolution of Subg.Eriocoryne and Subg.Amphilaena is mainly based on the structural variation at the diploid level.The crosses and polyploidy,had little effect on the formation of new species in the two subgenus.(2)The analysis of karyotype asymmetry showed that the relationship between the Subg.Eriocoryne and Subg.Amphilaena was closer,which was consistent with the traditional taxonomic results.The correlation analysis between CV_CI and M_CAA showed that the evolution of chromosomes in the two subgenus was the result of changes in the length of the chromosomes,the genetic material on the longer arm of the shorter chromosome was transferred to the shorter arm.The correlation analysis between CV_CL and THL showed that the length of the chromosomes changed,but the sum of their haploid lengths remained basically unchanged.It is speculated that the differences in genome size between the two subgenus species are small.(3)CV_CL,CV_CI,THL,and M_CA were used to perform cluster analysis on the study groups.The results showed that,the karyotype parameters in the two subgenus were less variable,except Saussurea medusa.The results of flow cytometry on nuclear DNA content showed:(1)Genome size differences between the two subgenus species are small.The nuclear DNA content of the two subgenus is between 7-9 pg,with no significant differences between species.(2)Comparing the populations,it was found that,except Saussurea polycolea was tetraploid,the remaining 66 populations were diploid.It is further proved that the ploidy level of Subg.Eriocoryne and Subg.Amphilaena is mainly diploid;traditional"polyploid pre-adaptation mechanism"or the hypothesis that polyploid is more able to adapt to harsh environments is invalid;the predominance of diploids also implies to a certain extent that the geological history of the region may be less affected by the glacial period,and did not promote the formation of polyploids,allowing the diploids distributed in this area to be widely preserved.(3)The nuclear DNA content of Saussurea medusa fluctuates within a small range.This result may be caused by differences in genetic information of individuals growing in different habitats,which is consistent with the results of cluster analysis.It is speculated that there are differences in genetic material between populations in Saussurea medusa,not only in the amount of nuclear DNA,but also in the chromosome morphology.There were no significant differences in nuclear DNA content among the remaining 16 species,and the ploidy level in Saussurea had a small effect on the 1Cx-value(the DNA content of the haploid component genome).(4)Combined with the altitude analysis showed that the higher the altitude of Subg.Eriocoryne and Subg.Amphilaena,the more evolved their chromosomes.The nuclear DNA contents are not associated with altitude.In response to extreme environments such as low temperature,high ultraviolet radiation,and large temperature differences,the chromosomes of the two subgenus plants have evolved with the increase in the intensity of external interference,which is mainly reflected by the increased degree of chromosome length variation,but the haploid components of genome size has not increased.