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71.
A mycological survey was carried out on rice samples harvested in 1997 and 1998 from Entre Ríos province, belonging to the
main production area of Argentina. The relative density and isolation frequency of the prevalent fungi were statistically
compared between locations and harvest seasons. The genusAlternaria was the most prevalent component of the internal seedborne mycoflora in the two harvest seasons. Fungi belonging to the generaPhoma, Fusarium, Microdochium, Penicillium andAspergillus were also isolated. The predominant species of these genera wereAlternaria alternata, Phoma glomerata, Fusarium graminearum, Microdochium nivale, Penicillium citrinum and Aspergillus flavus. 相似文献
72.
LAËTITIA BUISSON WILFRIED THUILLER SOVAN LEK PUY LIM GAËL GRENOUILLET 《Global Change Biology》2008,14(10):2232-2248
Stream fish are expected to be significantly influenced by climate change, as they are ectothermic animals whose dispersal is limited within hydrographic networks. Nonetheless, they are also controlled by other physical factors that may prevent them moving to new thermally suitable sites. Using presence–absence records in 655 sites widespread throughout nine French river units, we predicted the potential future distribution of 30 common stream fish species facing temperature warming and change in precipitation regime. We also assessed the potential impacts on fish assemblages' structure and diversity. Only cold-water species, whose diversity is very low in French streams, were predicted to experience a strong reduction in the number of suitable sites. In contrast, most cool-water and warm-water fish species were projected to colonize many newly suitable sites. Considering that cold headwater streams are the most numerous on the Earth's surface, our results suggested that headwater species would undergo a deleterious effect of climate change, whereas downstream species would expand their range by migrating to sites located in intermediate streams or upstream. As a result, local species richness was forecasted to increase greatly and high turnover rates indicated future fundamental changes in assemblages' structure. Changes in assemblage composition were also positively related to the intensity of warming. Overall, these results (1) stressed the importance of accounting for both climatic and topographic factors when assessing the future distribution of riverine fish species and (2) may be viewed as a first estimation of climate change impacts on European freshwater fish assemblages. 相似文献
73.
Throughout the animal kingdom there are species that have two or more phenotypic forms or 'morphs', and many of these are amphibians. In North America, the red-backed salamander Plethodon cinereus can have either a red dorsal stripe or no dorsal stripe (lead-phase form), and evidence to date indicates the lead-phase form incurs a greater number of attacks from predators. In a recent collection of 51 P. Cinereus, blood smears of both color morphs (35 red-stripe, 16 lead-phase) were examined to obtain numbers of circulating leukocytes (via light microscopy), which can be used to indirectly estimate levels of stress hormones in vertebrates via a 'hematological stress index', which is the ratio between the number of two leukocyte types (neutrophils and lymphoeytes). Our results showed that lead-phase salamanders tended to have greater numbers of circulating neutrophils and lower numbers of circulating iymphocytes than red-stripe morphs, leading to higher average neutrophil-lymphocyte ratios in lead-phase individuals. Since the salamanders were held (refrigerated) for 7 days before sampling, we cannot be certain if this effect is a stress reaction to the captivity or the normal level for this morph. However comparison with two sets of related salamanders that were captured and sampled immediately indicates the red-stripe salamanders were either not stressed from the captivity at all, or their white blood cell distributions had returned to normal after 7 days of captivity. Taken together, our results indicate that lead-phase forms of P. Cinereus have higher stress levels than the red-stripe forms, which may be a consequence of their higher exposure to, and/or attacks from, predators. They may also indicate that the lead-phase form is less-suited to captivity than the red-stripe form of this species. 相似文献
74.
Effects of heat shock, stannous chloride, and gallium nitrate on the rat inflammatory response 下载免费PDF全文
House SD Guidon PT Perdrizet GA Rewinski M Kyriakos R Bockman RS Mistry T Gallagher RA Hightower LE 《Cell stress & chaperones》2001,6(2):164-171
Heat and a variety of other stressors cause mammalian cells and tissues to acquire cytoprotection. This transient state of altered cellular physiology is nonproliferative and antiapoptotic. In this study, male Wistar rats were stress conditioned with either stannous chloride or gallium nitrate, which have immunosuppressive effects in vivo and in vitro, or heat shock, the most intensively studied inducer of cytoprotection. The early stages of inflammation in response to topical suffusion of mesentery tissue with formyl-methionyl-leucyl-phenylalanine (FMLP) were monitored using intravital microscopy. Microvascular hemodynamics (venular diameter, red blood cell velocity [Vrbc], white blood cell [WBC] flux, and leukocyte-endothelial adhesion [LEA]) were used as indicators of inflammation, and tissue levels of inducible Hsp70, determined using immunoblot assays, provided a marker of cytoprotection. None of the experimental treatments blocked decreases in WBC flux during FMLP suffusion, an indicator of increased low-affinity interactions between leukocytes and vascular endothelium known as rolling adhesion. During FMLP suffusion LEA, an indicator of firm attachment between leukocytes and vascular endothelial cells increased in placebo and gallium nitrate-treated animals but not in heat- and stannous chloride-treated animals, an anti-inflammatory effect. Hsp70 was not detected in aortic tissue from placebo and gallium nitrate-treated animals, indicating that Hsp70-dependent cytoprotection was not present. In contrast, Hsp70 was detected in aortic tissues from heat- and stannous chloride-treated animals, indicating that these tissues were in a cytoprotected state that was also an anti-inflammatory state. 相似文献
75.
76.
77.
Evolution of the secondary structures and compensatory mutations of the ribosomal RNAs of Drosophila melanogaster 总被引:10,自引:0,他引:10
This paper examines the effects of DNA sequence evolution on RNA secondary
structures and compensatory mutations. Models of the secondary structures
of Drosophila melanogaster 18S ribosomal RNA (rRNA) and of the complex
between 2S, 5.8S, and 28S rRNAs have been drawn on the basis of comparative
and energetic criteria. The overall AU richness of the D. melanogaster
rRNAs allows the resolution of some ambiguities in the structures of both
large rRNAs. Comparison of the sequence of expansion segment V2 in D.
melanogaster 18S rRNA with the same region in three other Drosophila
species and the tsetse fly (Glossina morsitans morsitans) allows us to
distinguish between two models for the secondary structure of this region.
The secondary structures of the expansion segments of D. melanogaster 28S
rRNA conform to a general pattern for all eukaryotes, despite having highly
divergent sequences between D. melanogaster and vertebrates. The 70 novel
compensatory mutations identified in the 28S rRNA show a strong (70%) bias
toward A-U base pairs, suggesting that a process of biased mutation and/or
biased fixation of A and T point mutations or AT-rich slippage-generated
motifs has occurred during the evolution of D. melanogaster rDNA. This
process has not occurred throughout the D. melanogaster genome. The
processes by which compensatory pairs of mutations are generated and spread
are discussed, and a model is suggested by which a second mutation is more
likely to occur in a unit with a first mutation as such a unit begins to
spread through the family and concomitantly through the population.
Alternatively, mechanisms of proofreading in stem-loop structures at the
DNA level, or between RNA and DNA, might be involved. The apparent
tolerance of noncompensatory mutations in some stems which are otherwise
strongly supported by comparative criteria within D. melanogaster 28S rRNA
must be borne in mind when compensatory mutations are used as a criterion
in secondary-structure modeling. Noncompensatory mutation may extend to the
production of unstable structures where a stem is stabilized by RNA-
protein or additional RNA-RNA interactions in the mature ribosome. Of
motifs suggested to be involved in rRNA processing, one (CGAAAG) is
strongly overrepresented in the 28S rRNA sequence. The data are discussed
both in the context of the forces involved with the evolution of multigene
families and in the context of molecular coevolution in the rDNA family in
particular.
相似文献
78.
Small-subunit ribosomal RNA sequence from Naegleria gruberi supports the polyphyletic origin of amoebas 总被引:2,自引:0,他引:2
We have sequenced the small-subunit ribosomal RNA gene of the amoebo-
flagellate protozoan Naegleria gruberi. Comparison of this sequence with
the rRNA sequences of other eukaryotes resulted in a phylogenetic tree that
supports the suggested polyphyletic origin of amoebas and suggests a
flagellate ancestry for Naegleria.
相似文献
79.
Cross-hybridizing snake satellite, Drosophila, and mouse DNA sequences may have arisen independently 总被引:2,自引:0,他引:2
Previous reports have interpreted hybridization between snake satellite DNA
and DNA clones from a variety of distant taxonomic groups as evidence for
evolutionary conservation, which implies common ancestry (homology) and/or
convergence (analogy) to produce the cross- hybridizing sequences. We have
isolated 11 clones from a genomic library of Drosophila melanogaster, using
a cloned 2.5-kb snake satellite probe of known nucleotide sequence. We have
also analysed published sequence data from snakes, mice, and Drosophila.
These data show that (1) all of the cross-hybridization between the snake,
fly, and mouse clones can be accounted for by the presence of either of two
tandem repeats, [GATA]n and [GACA]n and (2) these tandem repeats are
organized differently among the different species. We find no evidence that
these sequences are homologous apart from the existence of the simple
repeat itself, although their divergence from a common ancestral sequence
cannot be ruled out. The sequences contain a variety of homogeneous
clusters of tandem repeats of CATA, GA, TA, and CA, as well as GATA and
GACA. We suggest that these motifs may have arisen by a self-accelerating
process involving slipped-strand mispairing of DNA. Homogeneity of the
clusters might simply be the result of a rate of accumulation of tandem
repeats that exceeds that of other mutations.
相似文献
80.