Toward a realistic model of mutations affecting fitness

Analysis of a recent mutation accumulation (MA) experiment has led to the suggestion that as many as one-half of spontaneous mutations in Arabidopsis are advantageous for fitness. We evaluate this in the light of data from other MA experiments, along with molecular evidence, that suggest the vast majority of new mutations are deleterious.     

Accumulation of heavy metals in epidermal glands of the waterlily (Nymphaeaceae)

This study investigates the anatomical aspects of heavy-metal accumulation in the waterlily (Nymphaea `Aurora', Nymphaeaceae). Epidermal glands were identified by light microscopy on the abaxial side of the leaf laminae and on the epidermis of the rhizome; glandular trichomes were observed in the petiole epidermis. Glands were not observed in the roots. Accumulation of heavy metals in these glands was monitored using a scanning electron microscope equipped for energy-dispersive spectroscopy. Further experiments showed maximal cadmium and calcium accumulation in the mature leaf lamina in daylight, and this accumulation was inhibited by the herbicide 3-(3′,4′-dichlorophenyl)-1,1-dimethylurea. These results suggest that, in Nymphaea, heavy metals are accumulated primarily in association with glands found in plant organs that have direct contact with water or mud. Deposition and storage of heavy metals by these glands may represent a stage in the sequestration and detoxification of the metals. Our results raise the possibility of utilizing waterlilies for the removal of heavy metals from polluted environments. Received: 29 April 2000 / Accepted: 8 June 2000     

Influence of glutethimide on rat brain mononucleotides by sub-chronic codeine treatment

It was investigated the in vivo effect of glutethimide on the intracellular neuroadaptation characteristic for μ-opioid receptor tolerance induced by chronic codeine treatment and reflected by increased levels of adenylyl cyclase (AC) and cAMP-dependent protein kinase (PKA). AC activity was appreciated by cyclic-AMP (cAMP) formation, the levels of adenine and guanine nucleotides in brain extracts being assayed using a high performance liquid chromatographic method. The concomitant chronic administration of codeine and glutethimide resulted in a pronounced and long-lasting energetic depletion of the neurons, consistent with the high risk of overdose, and increase of cAMP's stable metabolite, 5'-AMP. This increase is persistent even after withdrawal and suggests an interference with the adenylyl cyclase system involved in the development of tolerance of opioid receptor and in relapse and provides a possible explanation of addiction and fast increase of doses observed in humans abusing this combination.     

A comprehensive model of mutations affecting fitness and inferences for Arabidopsis thaliana

As the ultimate source of genetic variation, spontaneous mutation is essential to evolutionary change. Theoretical studies over several decades have revealed the dependence of evolutionary consequences of mutation on specific mutational properties, including genomic mutation rates, U, and the effects of newly arising mutations on individual fitness, s. The recent resurgence of empirical effort to infer these properties for diverse organisms has not achieved consensus. Estimates, which have been obtained by methods that assume mutations are unidirectional in their effects on fitness, are imprecise. Both because a general approach must allow for occurrence of fitness-enhancing mutations, even if these are rare, and because recent evidence demands it, we present a new method for inferring mutational parameters. For the distribution of mutational effects, we retain Keightley's assumption of the gamma distribution, to take advantage of the flexibility of its shape. Because the conventional gamma is one sided, restricting it to unidirectional effects, we include an additional parameter, rho, as an amount it is displaced from zero. Estimation is accomplished by Markov chain Monte Carlo maximum likelihood. Through a limited set of simulations, we verify the accuracy of this approach. We apply it to analyze data on two reproductive fitness components from a 17-generation mutation-accumulation study of a Columbia accession of Arabidopsis thaliana in which 40 lines sampled in three generations were assayed simultaneously. For these traits, U approximately/= 0.1-0.2, with distributions of mutational effects broadly spanning zero, such that roughly half the mutations reduce reproductive fitness. One evolutionary consequence of these results is lower extinction risks of small populations of A. thaliana than expected from the process of mutational meltdown. A comprehensive view of the evolutionary consequences of mutation will depend on quantitatively accounting for fitness-enhancing, as well as fitness-reducing, mutations.     

Evidence for the involvement of the RNA-dependent protein kinase (PKR) in the induction of human cytotoxic T lymphocytes against a synthetic peptide of HIV-1 by regulatory RNA

The studies on the inhibitory effect exerted by Cholera Toxin (CT) on cell growth and proliferation indicate a remarkable heterogeneity of cell response suggesting that the inhibition represents the final event of many different ways or mechanisms . After CT binding, cAMP accumulation may not occur (as in L1210 leukemia cells) or, when occurring (as in SR-4987 stromal cells), may not be coupled with the antiproliferative effect of CT. In WEHI-3B cells CT binds a Gal-GalNac-GM1b receptor and the anticlonogenic effect of CT seems correlated with cAMP accumulation.To demonstrate the central role of cAMP in WEHI-3B cells, starting from the sensitive cell strain we selected and established a clone of WEHI-3B resistant to CT. This revertant clone (WEHI-3B/CT/REV) is currently cultured in the absence of CT and in the proliferation assay shows a dramatic resistance (>46,000 than the parental cells). Stimulation of WEHI-3B/CT/REV cells by cholera toxin failed to enhance cAMP and the ganglioside-CT binding studied on Thin Layer Chromatography (TLC) blots showed that the resistant cells lost the spot correspondent to the migration of Gal-GalNac-GM1b ganglioside. Both the lines respond at the same level to the adenylate cyclase stimulation by forskolin and the incorporation of GM1a did not decrease the resistance of WEHI-3B/CT/REV. These data confirm that Gal-GalNac-GM1b is the most important functional receptor for CT in WEHI-3B cells able to transduce the signal by enhancing cAMP which in turn inhibits cell proliferation (probably by cAMP dependent protein kinase activation). Our study describes the first cell line resistant to CT originated from a susceptible parental strain and provides a new interesting cell model for studying the cAMP dependent mechanisms involved in cell growth regulation.     

Leprosy – clues about the biochemistry of Mycobacterium leprae and its host-dependency from the genome

Deletions and the appearance of pseudogenes in pathways of carbon source utilisation and energy metabolism best explain the host-dependency and failure to culture Mycobacterium leprae axenically. From the genome sequence it is possible to predict that acetate and galactose cannot be used as carbon sources, while pyruvate can only be catabolised. Glycerol, glucose, and fatty acids could be used for glycolysis, the pentose cycle and -oxidation which are complete. Retrospective functional genomics – interpreting work before the completion of the genome project – supports the failure of M. leprae to use acetate as well as another prediction that metabolic flux from pyruvate to acetyl-CoA would be very low. However, the loss of a second icd gene (compared with M. tuberculosis), predicted to encode isocitrate dehydrogenase, did not diminish the specific activity of the enzyme. The genes for respiratory pathways are extremely limited, being present for oxidative phosphorylation as a result of electron transport only using FADH as an electron donor. In contrast, all the major biosynthetic pathways are complete except that M. leprae is a natural methionine auxotroph: this is predicted not to be attenuating, or explain host-dependency since methionine would be present in rich culture media.     

Effects of oral aluminum on essential trace elements metabolism during pregnancy

The present study was conducted to assess in rats the effects of oral aluminum (Al) exposure on calcium (Ca), magnesium (Mg), manganese (Mn), copper (Cu), zinc (Zn), and iron (Fe) accumulation and urinary excretion. Three groups of plug-positive Sprague-Dawley (SD) rats were given by gavage 0, 200, and 400 mg/kg/d of Al(OH)₃ on gestational days 1–20. Three groups of nonpregnant female SD rats of the same age received Al(OH)₃ by gavage at the same doses for 20 consecutive days. At the end of the treatment period, 24-h urine samples were collected for analysis of Al and essential elements. Subsequently, all animals were sacrificed and samples of liver, bone, spleen, kidneys, and brain were removed for metal analyses. With some exceptions, the urinary amounts of Al, Mn, and Cu excreted by pregnant animals as well as the urinary levels of Al excreted by nonpregnant rats were higher in the Al-treated groups than in the respective control groups. Although higher Al levels were found in the liver of pregnant rats, the concentrations of Al in the brain of these animals were lower than those found in the same tissues of nonpregnant rats. With regard to the essential elements, tissue accumulation was most affected in pregnant than in nonpregnant animals. In pregnant rats, the hepatic and renal concentrations of Ca, Mg, Mn, Cu, Zn, and Fe, as well as the levels of Ca in bone, and the concentrations of Cu in brain were significantly higher in the Al-exposed groups than in the control group. According to the current results, oral Al exposure during pregnancy can produce significant changes in the tissue distribution of a number of essential elements.     

面包酵母海藻糖积累条件的研究

对面包酵母的海藻糖积累条件及补料分批发酵进行了研究。结果表明 pH为 5 .0 ,温度 37℃有利于海藻糖积累。少量多次的补加葡萄糖可持续增加海藻糖的含量 ,但随着发酵时间的延长 ,葡萄糖对海藻糖转化率有逐渐减少的趋势。     

Biogeochemical processes in intensive zero-effluent marine fish culture with recirculating aerobic and anaerobic biofilters

The biogeochemical processes that drive nutrient transformations and recycling in organic marine sediment-water environments were studied for 17 months in a zero-effluent intensive recirculating culture system. The system consisted of a 10 m³ gilthead seabream (Sparus aurata) tank coupled to aerobic and anaerobic water treatment elements. Nutrients and alkalinity were measured in the system to quantify the main biogeochemical processes. Fractions of the carbon fed in feed were found in fish (18.3%) and in sludge (11%); the missing carbon was respired by fish (45%) and by aerobic (8.4%) and anaerobic (7.7%) microorganisms. Fractions of the nitrogen fed in feed were found in fish (15.4%) and in sludge (14.3%); the missing nitrogen was eliminated by nitrification-denitrification. Most of the phosphorus and ash fed in feed and not found in fish accumulated within the sludge in the system. The rates of nitrification, denitrification and sulphate reduction increased with time, reaching 0.3 g N m^− 2 d^− 1, 53 g N m^− 2 d^− 1 and 145 g S m^− 2 d^− 1, respectively. Nitrification developed more rapidly than denitrification, leading at first to nitrate accumulation (to 20 mmol NO₃ l^− 1 by day 200) and a decrease in alkalinity. Once denitrification surpassed nitrification, nitrate concentrations decreased, eventually being reduced to < 0.3 mmol NO₃ l^− 1 by day 510, and alkalinity stabilized. Toxic hydrogen sulphide, generated within the anaerobic sludge, was oxidized by oxygen and nitrate as it diffused through the anaerobic-aerobic sediment-water interface. When nitrate levels in the water above the sludge dropped below 2 mmol l^− 1, sulphide was also oxidized in the fluidized bed reactor. Denitrification reduced nitrate in the water, respired (jointly with sulphate reduction) carbon in the sludge, oxidized the hydrogen sulphide, and contributed to stabilization of alkalinity and accumulation of polyphosphate in bacteria as a major sink of labile P.     

Cellular compartmentation of cadmium and zinc in relation to other elements in the hyperaccumulator Arabidopsis halleri

The cellular compartmentation of elements was analysed in the Zn hyperaccumulator Arabidopsis halleri (L.) O'Kane & Al-Shehbaz (=Cardaminopsis halleri) using energy-dispersive X-ray microanalysis of frozen-hydrated tissues. Quantitative data were obtained using oxygen as an internal standard in the analyses of vacuoles, whereas a peak/background ratio method was used for quantification of elements in pollen and dehydrated trichomes. Arabidopsis halleri was found to hyperaccumulate not only Zn but also Cd in the shoot biomass. While large concentrations of Zn and Cd were found in the leaves and roots, flowers contained very little. In roots grown hydroponically, Zn and Cd accumulated in the cell wall of the rhizodermis (root epidermis), mainly due to precipitation of Zn/Cd phosphates. In leaves, the trichomes had by far the largest concentrations of Zn and Cd. Inside the trichomes there was a striking sub-cellular compartmentation, with almost all the Zn and Cd being accumulated in a narrow ring in the trichome base. This distribution pattern was very different from that for Ca and P. The epidermal cells other than trichomes were very small and contained lower concentrations of Zn and Cd than mesophyll cells. In particular, the concentrations of Cd and Zn in the mesophyll cells increased markedly in response to increasing Zn and Cd concentrations in the nutrient solution. This indicates that the mesophyll cells in the leaves of A. halleri are the major storage site for Zn and Cd, and play an important role in their hyperaccumulation. Received: 4 April 2000 / Accepted: 16 May 2000