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An explant containing the primary shoot meristem was dissected from intact tomato seedlings after thawing from liquid nitrogen. Surviving explants produced shoots directly by normal meristem growth when cultured in the presence of gibberellic acid. Without gibberellic acid all surviving explants produced callus tissue and subsequently adventitious shoots, with no direct outgrowth of the primary meristem.Dimethyl sulphoxide (15%) in culture medium and a cooling rate changing continuously from 20 to 55 °C min?1 between 0 and ?120 °C were required for optimal survival.Nonfrozen material produced shoots directly without the requirement for gibberellic acid indicating that hormonal regulation of organised growth by the shoot meristem had been altered by the freeze/ thaw process. 相似文献
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The climatic cycles with subsequent glacial and intergalcial periods have had a great impact on the distribution and evolution of species. Using genetic analytical tools considerably increased our understanding of these processes. In this review I therefore give an overview of the molecular biogeography of Europe. For means of simplification, I distinguish between three major biogeographical entities: (i) "Mediterranean" with Mediterranean differentiation and dispersal centres, (ii) "Continental" with extra-Mediterranean centres and (iii) "Alpine" and/or "Arctic" with recent alpine and/or arctic distribution patterns. These different molecular biogeographical patterns are presented using actual examples. Many "Mediterranean" species are differentiated into three major European genetic lineages, which are due to glacial isolation in the three major Mediterranean peninsulas. Postglacial expansion in this group of species is mostly influenced by the barriers of the Pyrenees and the Alps with four resulting main patterns of postglacial range expansions. However, some cases are known with less than one genetic lineage per Mediterranean peninsula on the one hand, and others with a considerable genetic substructure within each of the Mediterranean peninsulas, Asia Minor and the Maghreb. These structures within the Mediterranean sub-centres are often rather strong and in several cases even predate the Pleistocene. For the "Continental" species, it could be shown that the formerly supposed postglacial spread from eastern Palearctic expansion centres is mostly not applicable. Quite the contrary, most of these species apparently had extra-Mediterranean centres of survival in Europe with special importance of the perialpine regions, the Carpathian Basin and parts of the Balkan Peninsula. In the group of "Alpine" and/or "Arctic" species, several molecular biogeographical patterns have been found, which support and improve the postulates based on distribution patterns and pollen records. Thus, genetic studies support the strong linkage between southwestern Alps and Pyrenees, northeastern Alps and Carpathians as well as southeastern Alps and the Dinaric mountain systems, hereby allowing conclusions on the glacial distribution patterns of these species. Furthermore, genetic analyses of arctic-alpine disjunct species support their broad distribution in the periglacial areas at least during the last glacial period. The detailed understanding of the different phylogeographical structures is essential for the management of the different evolutionary significant units of species and the conservation of their entire genetic diversity. Furthermore, the distribution of genetic diversity due to biogeographical reasons helps understanding the differing regional vulnerabilities of extant populations. 相似文献
14.
AIMS: A DNA sequence, from Escherichia coli STEC O145, homologous to O-island 29 from STEC O157 is described, together with a real-time PCR assay for detecting it. METHODS AND RESULTS: PCR and sequencing were used to identify the 'O-island 29' homologous DNA sequence from STEC O145 (strain VTH34). The sequence divergence between the STEC O145 and O157 'O-island 29' allowed a STEC O145 5'-nuclease PCR assay to be developed. CONCLUSIONS: The characterization of a novel locus in STEC O145 has allowed a specific O145 serogroup 5'-nuclease PCR assay to be designed. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings increase the number of serogroup PCR assays available as alternatives to classical O-serotyping of E. coli. 相似文献
15.
AIMS: The aims of the study were to characterize the O91 O-antigen gene cluster from Shiga toxin-producing Escherichia coli (STEC) O91 and to provide the basis for a specific PCR test for rapid detection of E. coli O91. METHODS AND RESULTS: The published primers complementary to JUMPstart and gnd gene, the conserved flanking sequences of O-antigen genes clusters in E. coli and related species were used to amplify the 10-kbp O91 O-antigen biosynthesis locus of STEC O91. A DNA library representative of this cluster allowed two O91 specific probes to be identified, and two specific PCR O91 serotyping tests to be successfully developed. CONCLUSIONS: These results confirm that the O-antigen gene cluster sequences of E. coli allow rapidly a specific O-antigen PCR assay to be designed. SIGNIFICANCE AND IMPACT OF THE STUDY: These findings increase the number of PCR-assays available to replace the classical O-serotyping among E. coli O-antigen. 相似文献
16.
In Hevea, currently described culture conditions allow the induction of two modes of embryogenesis in callus formed on excised portions of the internal integument of immature seeds. One mode is of unicellular origin and is transitory, only resulting in the production of globular proembryos. The other is of multicellular origin and produces embryos. Specific culture conditions appear to favor one or the other mode of development in a given genotype. The ontogenesis of embryos of multicellular origin bypasses the classical stages of zygotic embryogenesis. The structural abnormalities observed in most somatic embryos are probably responsible for the low germination rates obtained. 相似文献
17.
We investigated the ultrastructure and metabolic capabilities of isolated rat hepatocytes after cryopreservation using 1.5 M Me2SO as protectant and a slow cool/fast thaw regime. Ultrastructural assessment of the cryopreserved population revealed only approximately 10% of cells with normal morphology. Conjugation of bilirubin by the cryopreserved cells was reduced to 20% of that seen in unfrozen hepatocytes and there was a net loss of glycogen measured in cryopreserved cells incubated in conditions which stimulated glycogen synthesis by unfrozen cells. These results are in contrast to other reports in which cryopreserved hepatocytes have been successfully used for transplantation to reverse hepatic insufficiency. 相似文献
18.
Yipeng?ZhaoEmail author Brian?W.?W.?Grout Andy?V.?Roberts 《Plant Cell, Tissue and Organ Culture》2005,83(3):335-338
Rhubarb (Rheum rhaponticum L.) is a tetraploid (2n = 44) vegetable crop growing in Europe and North America. The results observed 44 chromosomes for both cultivars Timperly Early and PC49, but showing significant differences in DNA contents between them. Abnormal chromosome numbers (2n = 22 and 32) and chromosomal fragments were observed only in micropropagated plants of rhubarb PC49, suggesting somaclonal variation. The results provide further information on understanding morphological variation and increased disease susceptibility of micropropagated rhubarb PC49 in our previous investigation. 相似文献
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Jochen BW Wolf Chris Harrod Sylvia Brunner Sandie Salazar Fritz Trillmich Diethard Tautz 《BMC evolutionary biology》2008,8(1):150