Identification of Four C40 Isomers by Means of a Theoretical XPS/NEXAFS Spectra Study.

XPS and NEXAFS spectra of four stable C40 isomers [29( C2), 31( C s), 38( D2), and 39( D5 d)] have been investigated theoretically. We combined density functional theory and the full core hole potential method to simulate C 1s XPS and NEXAFS spectra for nonequivalent carbon atoms of four stable C40 fullerene isomers. The NEXAFS showed obvious dependence on the four C40 isomers, and XPS spectra are distinct for all four isomers, which can be employed to identify the four stable structures of C40. Furthermore, the individual components of the spectra according to different categories have been investigated, and the relationship between the spectra and the local structures of C atoms was also explored.

Comparative chromosomal localization of 45S and 5S rDNAs and implications for genome evolution in Cucumis.

Ribosomal DNAs are useful cytogenetic markers for chromosome analysis. Studies investigating site numbers and distributions of rDNAs have provided important information for elucidating genome organization and chromosomal relationships of many species by fluorescence in situ hybridization. But relevant studies are scarce for species of the genus Cucumis, especially in wild species. In the present study, FISH was conducted to investigate the organization of 45S and 5S rDNA among 20 Cucumis accessions, including cultivars and wild accessions. Our results showed that the number of 45S rDNA sites varied from one to five pairs in different accessions, and most of these sites are located at the terminal regions of chromosomes. Interestingly, up to five pairs of 45S rDNA sites were observed in C. sativus var. sativus, the species which has the lowest chromosome number, i.e., 2n = 14. Only one pair of 5S rDNA sites was detected in all accessions, except for C. heptadactylus, C. sp, and C. spp that had two pairs of 5S rDNA sites. The distributions of 5S rDNA sites showed more variation than 45S rDNA sites. The phylogenetic analysis in this study showed that 45S and 5S rDNA have contrasting evolutionary patterns. We find that 5S rDNA has a polyploidization-related tendency towards the terminal location from an interstitial location but maintains a conserved site number, whereas the 45S rDNA showed a trend of increasing site number but a relatively conserved location.