Algal turf communities are ubiquitous on coral reefs in the Caribbean and are often dominated by N2-fixing cyanobacteria. However, it is largely unknown (1) how much N2 is actually fixed by turf communities and (2) which factors affect their N2 fixation rates. Therefore, we compared N2 fixation activity by turf communities at different depths and during day and night-time on a degraded versus a less degraded coral reef site on the island of Curaçao. N2 fixation rates measured with the acetylene reduction assay were slightly higher in shallow (5–10-m depth) than in deep turf communities (30-m depth), and N2 fixation rates during the daytime significantly exceeded those during the night. N2 fixation rates by the turf communities did not differ between the degraded and less degraded reef. Both our study and a literature survey of earlier studies indicated that turf communities tend to have lower N2 fixation rates than cyanobacterial mats. However, at least in our study area, turf communities were more abundant than cyanobacterial mats. Our results therefore suggest that turf communities play an important role in the nitrogen cycle of coral reefs. N2 fixation by turfs may contribute to an undesirable positive feedback that promotes the proliferation of algal turf communities while accelerating coral reef degradation. 相似文献
Parkinson’s disease (PD), defined as a neurodegenerative disorder, is characterized by the loss of dopaminergic neurons in the substantia nigra in the midbrain. Loss-of-function mutations in the parkin gene are a major cause of autosomal recessive, early-onset PD. Parkin has been implicated in the maintenance of healthy mitochondria, although previous studies show conflicting findings regarding mitochondrial abnormalities in fibroblasts from patients harboring parkin-null mutations. The aim of the present study was to determine whether South African PD patients with parkin mutations exhibit evidence for mitochondrial dysfunction. Fibroblasts were cultured from skin biopsies obtained from three patients with homozygous parkin-null mutations, two heterozygous mutation carriers and two wild-type controls. Muscle biopsies were obtained from two of the patients. The muscle fibers showed subtle abnormalities such as slightly swollen mitochondria in focal areas of the fibers and some folding of the sarcolemma. Although no differences in the degree of mitochondrial network branching were found in the fibroblasts, ultrastructural abnormalities were observed including the presence of electron-dense vacuoles. Moreover, decreased ATP levels which are consistent with mitochondrial dysfunction were observed in the patients’ fibroblasts compared to controls. Remarkably, these defects did not manifest in one patient, which may be due to possible compensatory mechanisms. These results suggest that parkin-null patients exhibit features of mitochondrial dysfunction. Involvement of mitochondria as a key role player in PD pathogenesis will have important implications for the design of new and more effective therapies. 相似文献
Above‐ and belowground herbivores promote plant diversity when selectively feeding on dominant plant species, but little is known about their combined effects. Using a model system, we show that neutral effects of an aboveground herbivore and positive effects of a belowground herbivore on plant diversity became profoundly negative when adding these herbivores in combination. The non‐additive effects were explained by differences in plant preference between the aboveground‐ and the belowground herbivores and their consequences for indirect interactions among plant species. Simultaneous exposure to aboveground‐ and belowground herbivores led to plant communities being dominated by a few highly abundant species. As above‐ and belowground invertebrate herbivores generally differ in their mobility and local distribution patterns, our results strongly suggest that aboveground–belowground interactions contribute to local spatial heterogeneity of diversity patterns within plant communities. 相似文献
Molecular dynamics simulations have been performed on netropsin in two different charge states and on distamycin binding to the minor groove of the DNA duplex d(CGCGAAAAACGCG)·d(CGCGTTTTTCGCG). The relative free energy of binding of the two non-covalently interacting ligands was calculated using the thermodynamic integration method and reflects the experimental result. From 2 ns simulations of the ligands free in solution and when bound to DNA, the mobility and the hydrogen-bonding patterns of the ligands were studied, as well as their hydration. It is shown that even though distamycin is less hydrated than netropsin, the loss of ligand–solvent interactions is very similar for both ligands. The relative mobilities of the ligands in their bound and free forms indicate a larger entropic penalty for distamycin when binding to the minor groove compared with netropsin, partially explaining the lower binding affinity of the distamycin molecule. The detailed structural and energetic insights obtained from the molecular dynamics simulations allow for a better understanding of the factors determining ligand–DNA binding. 相似文献
The World Health Organization (WHO) has a commitment to helping Member States achieve safe, sustainable and health-enhancing human environments, protected from biological, chemical and physical agents. The latter includes advising on the health impact of electromagnetic fields (EMFs) and radiation.
The results of the WHO/ICNIRP/NRPB workshop on static magnetic fields, published in this volume, provide a valuable and much needed contribution to the health risk assessment of exposure to static electric and magnetic fields, which is currently being coordinated by the WHO's International EMF Project. This WHO health risk assessment will be published as an environmental health criteria (EHC) monograph in early 2005.
This paper briefly gives an overview of the process of developing the WHO static fields EHC monograph, the criteria applied to studies that could contribute to the EHC, along with the ‘weight-of-evidence’ approach to health risk assessment. In addition, there is an increasing awareness of the need to account for uncertainty in the science database. This is traditionally addressed by further research, and the EMF project addresses these needs through the development of a ‘research agenda’. However, research programmes may take several years to complete, and the long latency associated with diseases such as cancer in people may also preclude a rapid outcome in some studies. The issue of current uncertainty is being addressed by the WHO EMF project through the development of a ‘precautionary framework’ in which precautionary measures will be applied to policy recommendations. 相似文献
Synopsis Many recognised species of coral reef fishes exhibit two or more colour variants, but it is unknown whether these represent
genetically identical phenotypes, genetic polymorphisms or closely related species. We tested between these alternatives for
two colour morphs of the coral reef fish, Pseudochromis fuscus, from Lizard Island (Great Barrier Reef). A molecular analysis using mtDNA did not detect any genetic differentiation between
co-occurring ‘yellow’ and ‘brown’ colour morphs. A previous study proposed that these two colour morphs are aggressive mimics
of yellow and brown damselfishes. Here, a manipulative field experiment was used to evaluate whether the colour dimorphism
in P. fuscus is a phenotypic response to the presence of two different model species. Colonies of either yellow or brown damselfish species
were established on different patch reefs, and each of the two different P. fuscus morphs was then placed on the different reefs. Contrary to expectations, all yellow individuals that stayed on the reefs
changed to brown, regardless of the model species. No brown individuals changed to the yellow colouration. However, P. fuscus were more likely to emigrate from, or suffer higher mortality on, patch reefs where they were not matched with similarly
coloured models. Clearly, yellow and brown P. fuscus are members of a single species with sufficient phenotypic plasticity to switch from yellow to brown colouration. 相似文献
The localization to 19q of the gene causing myotonic dystrophy (DM) has been defined more precisely by refinement of the physical location of several linked markers. A somatic cell hybrid mapping panel from cells with t(1;19), t(12;19), and t(X;19) translocation products was constructed to define five different intervals across 19q. In addition, we have derived a series of cell hybrids by irradiation of a der(19)-only hybrid to further subdivide the cen-q13.1 region. Using an array of 36 cloned genes, anonymous DNAs, and enzyme markers, we have tested the location of the panel breakpoints and refined the regional assignment of several of these markers. All markers tightly linked to DM are localized mainly within 19q13.2, thus suggesting that the DM gene is also close to this region. 相似文献
Functional male sterility is an important trait for the production of hybrid seeds. Among the genes coding for functional male sterility in tomato is the positional sterility gene ps-2. ps-2 is monogenic recessive, confers non-dehiscent anthers and is the most suitable for practical uses. In order to have tools for molecular-assisted selection (MAS) we fine mapped the ps-2 locus. This was done in an F2 segregating population derived from the interspecific cross between a functionally male sterile line (ps-2/ps-2; Solanum lycopersicum) and a functionally male fertile line (S. pimpinellifolium). Here we report the procedure that has led to the high-resolution fine mapping of the ps-2 locus in a 1.65 cM interval delimited by markers T0958 and T0635 on the short arm of Chromosome 4. The presence of many COS markers in the local high-resolution map allowed us to study the synteny between tomato and Arabidopsis at the ps-2 locus region. No obvious candidate gene for ps-2 was identified among the known functional male sterility genes in Arabidopsis. 相似文献
Two quaternary ammonium silanes (QAS) were used to coat silicone rubber tracheoesophageal shunt prostheses, yielding a positively charged surface. One QAS coating [(trimethoxysilyl)-propyldimethyloctadecylammonium chloride] was applied through chemical bonding, while the other coating, Biocidal ZF, was sprayed onto the silicone rubber surface. The sprayed coating lost its stability within an hour, while the chemically bonded coating appeared stable. Upon incubation in an artificial throat model, allowing simultaneous adhesion and growth of yeast and bacteria, all coated prostheses showed significant reductions in the numbers of viable yeast (to 12% to 16%) and bacteria (to 27% to 36%) compared with those for silicone rubber controls, as confirmed using confocal laser scanning microscopy after live/dead staining of the biofilms. In situ hybridization with fluorescently labeled oligonucleotide probes showed that yeasts expressed hyphae on the untreated and Biocidal ZF-coated prostheses but not on the QAS-coated prostheses. Whether this is a result of the positive QAS coating or is due to the reduced number of bacteria is currently unknown. In summary, this is the first report on the inhibitory effects of positively charged coatings on the viability of yeasts and bacteria in mixed biofilms. Although the study initially aimed at reducing voice prosthetic biofilms, its relevance extends to all biomedical and environmental surfaces where mixed biofilms develop and present a problem. 相似文献