Studies On The Cytology And Molecular Phylogeny On Cupressus Chenegiana S.Y.Hu

Cupressus chengiana S.Y.Hu, a long-lived conifer of the genus Cupressus in Cupressaceae, is an endangered species endemic to Sichuan and Gansu Province in China, which has been nominated as the 2nd class protection plants in . The nature populations of C. chenegiana distributed restrictedly to the upper reaches of Minjiang, Daduhe and Balonghe rivers at elevations from 1000 to 2600m, which are characterized by rainless, high evaporation and windiness. C. chengiana is tolerant of drought and coldness so that it can grow in various sorts of droughty and lean soils, even on the petrous apertures. And it is one of the most important plants for forestation, soil and water conservation in the dry valley in Sichuan province, because of its fine capability of water resources conservation. In the past years, it had been used to built temples, boats and lots of traditional Chinese farm tools for its fine woodiness and special balm. Recently, the distribution areas of C. chenegiana dwindled gradually andindividuals became fewer sharply owing to badly destroyed environments, over-logging, grazing and its biological characteristic. It is essential to excute studies on conservation genetics of C. chengiana for discussing its extinct mechanism. To estimate the level and distribution of genetic variation in endangered species is a primary objective of conservation genetics.The knowledge concerning about C. chengiana's genetic backgrounds were still unknown expect some reports on its taxonomic position, chemical elements and karyomorphology. In the present paper, cytogenetics and molecular phylogeny were particular studied at the chromosome and DNA level,. The aims were to illuminate the genetics background of C. chenegiana and analyze the endangered mechanism, which offer cytogenetical evidences for the conservation implication. And discuss the systematic position of C. chenegiana in Chinese Cupressus species and the evolution of Chinese Cupressus plants. The results were as follows:1. The studies on the cytogenetics by karyotype, Fluorescence in Situ Hybridization (FISH) and Fluorochrome Banding.1) In the present paper, C. chenegiana were karyomorphologic investigated. The metaphase chromosome number was 22. The karyotype were formulated to be 2n=22=22m. The Relative length was between 3.83-5.38, the arm ratio was between 1.02-1.31, a'nd the average arm ratio was 1.16. There was one secondary constriction on the fourth and eighth chromosome respectively. The secondary constriction was on the small arm in the fourth chromosome and on large arm in the sixth. The karyotype asymmetry of the species was 1A type.2) There was one DAPI banding on the small arm in the fourth pairs of chromosome and on large arm in the eighth. Among the different populations, there are a few bandings and have no difference between populations. The results showed there was no obvious difference between each populations in C. chenegiana.2. Chinese Cupressus comprises five species. The molecular phylogenetic relationships of the species of Cupressus and Chamaecyparis were inferred bycomparing 479bp of chloroplast petG-trnP intergenic spacer sequence. In PAUP* analysis, Platycladus orientalis was used as the functional outgroup, the maximum likelihood method examined 1077 trees and found one tree with a best score of -Ln=2232.47. The phylogenetic tree shows that Chamaecyparis nootkatensis is clearly diverged from other Chamaecyparis species. Based on the results, together with evidence from other aspect, we consider that Cupressus funebris and Chamaecyparis nootkatensis should be placed in genus Cupressus. Utility of cpDNA intergenic spacer petG-trnP in Cupressus is also discussed.