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31.
Activity of aminoacyl-transfer-ribonucleic acid synthetases in tobacco-leaf tissue in relation to senescence and to the action of 6-furfurylaminopurine 总被引:8,自引:7,他引:8 下载免费PDF全文
1. Streptomyces griseus was grown in a medium containing l-[Me-(14)C]methionine, and the labelled products from an ethanolic extract of the cells were examined. 2. Acid hydrolysis of one of the products gave a compound identified as 3-O-[Me-(14)C]-methylmannose by a series of degradative reactions. 3. Reduction of the radioactive compound gave 3-O-methyl-d-mannitol, indistinguishable from a synthetic sample. 相似文献
32.
The fixation of a beneficial mutation represents the first step in adaptation, and the average effect of such mutations is therefore a fundamental property of evolving populations. It is nevertheless poorly characterized because the rarity of beneficial mutations makes it difficult to obtain reliable estimates of fitness. We obtained 68 genotypes each containing a single fixed beneficial mutation from experimental populations of Pseudomonas fluorescens, evolving in medium with serine as the sole carbon source and estimated the selective advantage of each by competition with the ancestor. The distribution of selection coefficients is modal and closely resembles the Weibull distribution. The average selection coefficient (2.1) and beneficial mutation rate (3.8x10(-8)) are high relative to previous studies, possibly because the ancestral population grows poorly in serine-limited medium. Our experiment suggests that the initial stages of adaptation to stressful environments will involve the substitution of mutations with large effect on fitness. 相似文献
33.
Julie A. Peterson John J. Obrycki James D. Harwood 《Biocontrol Science and Technology》2009,19(6):613-625
Despite the reported specificity of Bacillus thuringiensis proteins against target pests, a number of studies have indicated that the uptake of Bt-endotoxins from bioengineered crops could have negative effects on natural enemies. It is therefore essential to quantify exposure pathways in non-target arthropod food webs across multiple transgenic events. Adult ground beetles (Coleoptera: Carabidae) were collected from transgenic corn fields expressing lepidopteran-specific Cry1Ab, coleopteran-specific Cry3Bb1, and both Cry1Ab and Cry3Bb1 (stacked event), as well as a non-transgenic isoline. Carabid gut-contents were screened for Cry1Ab Bt-endotoxin using enzyme-linked immunosorbent assay. Significant numbers of carabids tested positive for Cry1Ab from the lepidopteran-specific field: Harpalus pensylvanicus (39%, 25 of 64), Stenolophus comma (4%, 6 of 136), Cratacanthus dubius (50%, 1 of 2), Clivina bipustulata (50%, 1 of 2), and Cyclotrachelus sodalis (20%, 1 of 5). The highest proportion of Bt-endotoxin uptake was 4–6 weeks post-anthesis. Only one species, H. pensylvanicus (5%, 4 of 75), screened positive for Cry1Ab from the stacked line, despite similar expression of this endotoxin in plant tissue harvested from both lines. This difference in Cry1Ab uptake could be due to changes in the non-target food web or differential rates of Bt-endotoxin decay between genetic events. This study has quantified the differential uptake of Cry1Ab Bt-endotoxin by the carabid community across multiple transgenic events, thus forming the framework for future risk-assessment of transgenic crops. 相似文献
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36.
J. G. Salway J. L. Harwood M. Kai G. L. White J. N. Hawthorne 《Journal of neurochemistry》1968,15(3):221-226
—The activities of four enzymes concerned with inositol lipid metabolism have been determined in homogenates of rat brains of different ages. The enzymes are CDP-diglyceride inositol phosphatidate transferase, phosphatidylinositol kinase, diphosphoinositide kinase and triphosphoinositide phosphomonoesterase. The activities of all the enzymes increased with age. Phosphatidylinositol kinase activity rose most sharply well before myelination, reaching a maximum at about 6 days of age. Diphosphoinositide kinase and triphosphoinositide phosphomonoesterase activities increased most rapidly during myelination. The increase in CDP-diglyceride inositol phosphatidate transferase showed no definite association with any period of development. It is concluded that triphosphoinositide metabolism is associated with myelin or a closely related structure. 相似文献
37.
Shah AH Abdelzaher AM Phillips M Hernandez R Solo-Gabriele HM Kish J Scorzetti G Fell JW Diaz MR Scott TM Lukasik J Harwood VJ McQuaig S Sinigalliano CD Gidley ML Wanless D Ager A Lui J Stewart JR Plano LR Fleming LE 《Journal of applied microbiology》2011,110(6):1571-1583
Aims: Research into the relationship between pathogens, faecal indicator microbes and environmental factors in beach sand has been limited, yet vital to the understanding of the microbial relationship between sand and the water column and to the improvement of criteria for better human health protection at beaches. The objectives of this study were to evaluate the presence and distribution of pathogens in various zones of beach sand (subtidal, intertidal and supratidal) and to assess their relationship with environmental parameters and indicator microbes at a non‐point source subtropical marine beach. Methods and Results: In this exploratory study in subtropical Miami (Florida, USA), beach sand samples were collected and analysed over the course of 6 days for several pathogens, microbial source tracking markers and indicator microbes. An inverse correlation between moisture content and most indicator microbes was found. Significant associations were identified between some indicator microbes and pathogens (such as nematode larvae and yeasts in the genus Candida), which are from classes of microbes that are rarely evaluated in the context of recreational beach use. Conclusions: Results indicate that indicator microbes may predict the presence of some of the pathogens, in particular helminthes, yeasts and the bacterial pathogen Staphylococcus aureus including methicillin‐resistant forms. Indicator microbes may thus be useful for monitoring beach sand and water quality at non‐point source beaches. Significance and Impact of the Study: The presence of both indicator microbes and pathogens in beach sand provides one possible explanation for human health effects reported at non‐point sources beaches. 相似文献
38.
Mary Jane Rotheram-Borus Mark Tomlinson Ingrid M. le Roux Jessica M. Harwood Scott Comulada Mary J. O'Connor Robert E. Weiss Carol M. Worthman 《PloS one》2014,9(10)
Background
Interventions are needed to reduce poor perinatal health. We trained community health workers (CHWs) as home visitors to address maternal/infant risks.Methods
In a cluster randomised controlled trial in Cape Town townships, neighbourhoods were randomised within matched pairs to 1) the control, healthcare at clinics (n = 12 neighbourhoods; n = 594 women), or 2) a home visiting intervention by CBW trained in cognitive-behavioural strategies to address health risks (by the Philani Maternal, Child Health and Nutrition Programme), in addition to clinic care (n = 12 neighbourhoods; n = 644 women). Participants were assessed during pregnancy (2% refusal) and 92% were reassessed at two weeks post-birth, 88% at six months and 84% at 18 months later. We analysed 32 measures of maternal/infant well-being over the 18 month follow-up period using longitudinal random effects regressions. A binomial test for correlated outcomes evaluated overall effectiveness over time. The 18 month post-birth assessment outcomes also were examined alone and as a function of the number of home visits received.Results
Benefits were found on 7 of 32 measures of outcomes, resulting in significant overall benefits for the intervention compared to the control when using the binomial test (p = 0.008); nevertheless, no effects were observed when only the 18 month outcomes were analyzed. Benefits on individual outcomes were related to the number of home visits received. Among women living with HIV, intervention mothers were more likely to implement the PMTCT regimens, use condoms during all sexual episodes (OR = 1.25; p = 0.014), have infants with healthy weight-for-age measurements (OR = 1.42; p = 0.045), height-for-age measurements (OR = 1.13, p<0.001), breastfeed exclusively for six months (OR = 3.59; p<0.001), and breastfeed longer (OR = 3.08; p<0.001). Number of visits was positively associated with infant birth weight ≥2500 grams (OR = 1.07; p = 0.012), healthy head-circumference-for-age measurements at 6 months (OR = 1.09, p = 0.017), and improved cognitive development at 18 months (OR = 1.02, p = 0.048).Conclusions
Home visits to neighbourhood mothers by CHWs may be a feasible strategy for enhancing maternal/child outcomes. However, visits likely must extend over several years for persistent benefits.Trial Registration
ClinicalTrials.gov NCT00996528 相似文献39.
Rowan NJ MacGregor SJ Anderson JG Cameron D Farish O 《Applied and environmental microbiology》2001,67(6):2833-2836
The influence of treatment temperature and pulsed electric fields (PEF) on the viability of Mycobacterium paratuberculosis cells suspended in 0.1% (wt/vol) peptone water and in sterilized cow's milk was assessed by direct viable counts and by transmission electron microscopy (TEM). PEF treatment at 50 degrees C (2,500 pulses at 30 kV/cm) reduced the level of viable M. paratuberculosis cells by approximately 5.3 and 5.9 log(10) CFU/ml in 0.1% peptone water and in cow's milk, respectively, while PEF treatment of M. paratuberculosis at lower temperatures resulted in less lethality. Heating alone at 50 degrees C for 25 min or at 72 degrees C for 25 s (extended high-temperature, short-time pasteurization) resulted in reductions of M. paratuberculosis of approximately 0.01 and 2.4 log(10) CFU/ml, respectively. TEM studies revealed that exposure to PEF treatment resulted in substantial damage at the cellular level to M. paratuberculosis. 相似文献
40.
Acclimation of photosynthesis to increasing atmospheric CO2: The gas exchange perspective 总被引:9,自引:0,他引:9
Rowan F. Sage 《Photosynthesis research》1994,39(3):351-368
The nature of photosynthetic acclimation to elevated CO2 is evaluated from the results of over 40 studies focusing on the effect of long-term CO2 enrichment on the short-term response of photosynthesis to intercellular CO2 (the A/Ci response). The effect of CO2 enrichment on the A/Ci response was dependent on growth conditions, with plants grown in small pots (< 5 L) or low nutrients usually exhibiting a reduction of A at a given Ci, while plants grown without nutrient deficiency in large pots or in the field tended to exhibit either little reduction or an enhancement of A at a given Ci following a doubling or tripling of atmospheric CO2 during growth. Using theoretical interpretations of A/Ci curves to assess acclimation, it was found that when pot size or nutrient deficiency was not a factor, changes in the shape of A/Ci curves which are indicative of a reallocation of resources within the photosynthetic apparatus typically were not observed. Long-term CO2 enrichment usually had little effect or increased the value of A at all Ci. However, a minority of species grown at elevated CO2 exhibited gas exchange responses indicative of a reduced amount of Rubisco and an enhanced capacity to metabolize photosynthetic products. This type of response was considered beneficial because it enhanced both photosynthetic capacity at high CO2 and reduced resource investment in excessive Rubisco capacity. The ratio of intercellular to ambient CO2 (the Ci/Ca ratio) was used to evaluate stomatal acclimation. Except under water and humidity stress, Ci/Ca exhibited no consistent change in a variety of C3 species, indicating no stomatal acclimation. Under drought or humidity stress, Ci/Ca declined in high-CO2 grown plants, indicating stomata will become more conservative during stress episodes in future high CO2 environments.Abbreviations A
net CO2 assimilation rate
- Ci (Ca)
intercellular (ambient) partial pressure of CO2
- operational Ci
intercellular partial pressure of CO2 at a given ambient partial pressure of CO2
- gs
stomatal conductance
- normal CO2
current atmospheric mole fraction of CO2 (330 to 355 mol mol–1)
- Rubisco
ribulose-1,5-bisphosphate carboxylase/oxygenase 相似文献