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1.
Growth of 2-month-old nonnodulatedHippophaë rhamnoides seedlings supplied with combined N was compared with that of nodulated seedlings grown on zero N. Plant growth was significantly better with combined N than with N2 fixation and, although not statistically significant for individual harvests, tended to be highest in the presence of NH 4 + , a mixture of NH 4 + and NO 3 ? producing the highest yields. Growth was severely reduced when solely dependent on N2 fixation and, unlike the combined-N plants, shoot to root ratios had only slightly increased after an initial decrease. An apparently insufficient nodule mass (nodule weight ratio <5 per cent) during the greater part of the experimental period is suggested as the main cause of the growth reduction in N2-fixing plants. Thein vivo nitrate reductase activity (NRA) of NO 3 ? dependent plants was almost entirely located in the roots. However, when grown with a combination of NO 3 ? and NH 4 + , root NRA was decreased by approximately 85 per cent.H. rhamnoides demonstrated in the mixed supply a strong preference for uptake of N as NH 4 + , NO 3 ? contributing only for approximately 20 per cent to the total N assimilation. Specific rates of N acquisition and ion uptake were generally highest in NO 3 ? +NH 4 + plants. The generation of organic anions per unit total plant dry weight was approximately 40 per cent less in the NH 4 + plants than in the NO 3 ? plants. Measured extrusions of H+ or OH? (HCO 3 ? ) were generally in good agreement with calculated values on the basis of plant composition, and the acidity generated with N2 fixation amounted to 0.45–0.55 meq H+. (mmol Norg)?1. Without acidity control and in the presence of NH 4 + , specific rates of ion uptake and carboxylate generation were strongly depressed and growth was reduced by 30–35 per cent. Growth of nonnodulatedH. rhamnoides plants ceased at the lower pH limit of 3.1–3.2 and deterioration set in; in the case of N2-fixing plants the nutrient solution pH stabilized at a value of 3.8–3.9 without any apparent adverse effects upon plant performance. The chemical composition of experimental and field-growing plants is being compared and some comments are made on the nitrogen supply characteristics of their natural sites. 相似文献
2.
Biotic factors in the rhizosphere and their effect on the growth ofPlantago major L. ssp.pleiosperma Pilger (Great plantain) were studied. In a pot experiment the effect on shoot growth of the addition of 2.5% rhizosphere soil at four levels of phosphate was highly dependent on the availability of phosphate: a promoting effect at low phosphate levels was observed while a reducing effect occurred at higher phosphate levels. As the roots were infected with vesicular-arbuscular mycorrhizal (VAM) fungi in the treatment with rhizosphere soil, two other experiments were set up to separate effects of the indigenous VAM fungi from effects of the total rhizosphere population. The uptake of phosphate and shoot growth was not decreased at higher phosphate availability when VAM inoculum was added alone or in combination with rhizosphere soil. The growth reducing effect of the rhizosphere soil could therefore not be ascribed only to mycorrhizal infection. The results suggest that biotic factors in the rhizosphere soil affect the phosphate uptake ofPlantago major ssp.pleiosperma. This may, under conditions of phosphate limitation, lead to an increase of phosphate stress and, subsequently, a growth reduction. Futhermore, it is concluded that VAM fungi, as part of the rhizosphere population, may compensate this phosphate stress by enhancing the phosphate uptake.Grassland Species Research Group Publication No. 148. 相似文献
3.
C Troelstra R M Landsvater J Wiegant M van der Ploeg G Viel C H Buys J H Hoeijmakers 《Genomics》1992,12(4):745-749
We have cloned the human DNA excision repair gene ERCC6 by virtue of its ability to correct the uv sensitivity of Chinese hamster overy cell mutant UV61. This mutant is a member of complementation group 6 of the nucleotide excision repair-deficient rodent mutants. By means of in situ hybridization and Southern blot analysis of mouse x human somatic cell hybrids, the gene was localized to human chromosome 10q11-q21. An RFLP detected within the ERCC6 locus can be helpful in linkage analysis. 相似文献
4.
Two Dutch heathland sites Hoorneboeg (HB) and Ede, dominated by Deschampsia flexuosa and differing in nitrate production, were sampled for an entire growing season. A large number of soil and plant parameters were monitored in an attempt to assess the contribution of nitrate in the N supply and its assimilation by Deschampsia.Average NO3
– and NH4
+ concentrations (mg kg–1) in the top 10-cm depth were 0.03 and 2.2, respectively, for HB, and 2.1 and 6.7, respectively, for Ede. Laboratory incubations of intact cores and experiments with FH-layer suspensions showed significantly higher mineralization and nitrification rates for the Ede site during most of the season. Nitrification was largely controlled by the rate of net N-mineralization, which in turn was highly affected by soil moisture. Nitrate production was virtually zero at HB and accounted for 25% of the net N-mineralization at Ede.Shoot chemical composition showed no essential differences for the two sites, but mean in vivo (current) foliar NRA was almost 2-fold higher at Ede than at HB, indicating some utilization of nitrate at the former location. At the HB site with essentially no nitrate production, however, enzyme activities were clearly higher than basal constitutive levels in NH4
+-fed plants. Apparently, shoot NRA at the HB site became positively affected by factors other than nitrate availability and/or showed disproportional increases in response to atmospheric nitrate inputs. Root NRA displayed the same low basal level at the two sites. Nitrate fertilization (100 kg N ha–1) yielded maximally induced foliar NRAs similar to levels found in hydroponic nitrate plants. Although no accumulation of free NO3
– was observed in shoots from fertilized plots, increases in foliar concentrations of both organic N and carboxylates clearly indicated nitrate assimilation. Root NRA showed no response to nitrate addition.It is concluded that current NRA measurements in Deschampsia at heathland sites are of limited value only, especially when interpreted in isolation. A combined approach, using concurrently conducted soil and plant analyses, will allow the extent of nitrate utilization in the field to be best characterized.Publication 2013 of the Netherlands Institute of Ecology.FAX no corresponding author: +31 8306 23227 相似文献
5.
Nitrogen utilization by plant species from acid heathland soils: I. Comparison between nitrate and ammonium nutrition at constant low pH 总被引:4,自引:2,他引:2
Seven heathland species, four herbaceous plants and three dwarfshrubs, were tested for their capacity to utilize NH4+ or NO3. When cultured in solution at pH 4.0 with 2mol m3 N,all species showed similar growth responses with respect toN source. Nitrate was assimilated almost equally well as ammonium,with relative growth rate generally averaging 58% lowerfor NO3 grown plants, albeit not always significantly.However, N source was significantly and consistently correlatedwith biomass partitioning, as NH4+-fed plants allocated moredry matter to shoots and less to roots when compared to NO3-fed plants. The strong difference in biomass partitioning mayrelate to the relative surplus of carbon per unit plant N (or,alternatively, the relatively suboptimal rate of N assimilationper unit plantC) in NO3-fed plants Inherently slow-growing dwarf shrubs accumulated virtually nofree nitrate in their tissues and reduction of nitrate was strictlyroot-based. Faster-growing herbaceous plants, however, partitionedthe assimilation of nitrate over both shoots and roots, therebyaccumulating relatively high tissue NO3 levels. Ion uptakerates depended clearly on the relative shoot demand.At similar shoot demands, especially in the herbaceous species,specific uptake rates for N and total inorganic (non-N) anionswere higher in NH4+ -fed plants, whereas the uptake rate fortotal (non-N) cations was higher in NO3-fed plants. Rateof P uptake was enhanced with increasing plant demand, but wasindependent of the N source. Net H+ extrusions ranged from 1.00to 1.34 H+ per NH4+, and from 0.48 to 0.77 H+per NO3 taken up. Key words: Ammonium, biomass partitioning, heathland plants, low pH, nitrate, nitrate reductase activity, relative shoot demand, specific absorption rate 相似文献
6.
Maud N. Vissers Peter L. Zock Rianne Leenen Annet J.C. Roodenburg Karel P.A.M. Van Putte Martijn B. Katan 《Free radical research》2013,47(5):619-629
A high intake of olive oil has been proposed as an explanation for the low incidence of coronary heart disease in Mediterranean countries, but it is unclear whether olive oil offers specific benefits beyond a low content of saturated fat. Some types of extra virgin olive oil are rich in non-polar phenols, which might be taken up by plasma LDL particles and protect these from becoming atherogenic by oxidative modification. In a pilot study we found that consumption of 47 g fortified olive oil containing 31 mg phenols significantly increased the lag time of LDL oxidation from 112 ± 5 min before to 130 ± 7 min 2h after the meal. However, this study was not controlled, and in the current study we therefore investigated whether olive oil phenols increase the lag time of LDL oxidation in postprandial samples when compared with a control group.Twelve healthy men and women consumed four different olive oil supplements with a meal on four separate occasions: one similar to the supplement in the pilot study (positive control); one containing mainly non-polar olive oil phenols; one containing mainly polar olive oil phenols; and one without phenols (placebo). Lag time significantly increased 2 h after the meals with the positive control (8 ± 2 min), the polar phenols (8 ± 2 min), and the placebo (8 ± 2 min), but not after the non-polar phenols (-0.4 ± 3 min). Increases were not statistically different between supplements.These results indicate that the lag time of LDL-oxidation is increased after consumption of a meal. This increase is probably due to non-specific meal or time effects and not to phenols from olives or olive oil. Furthermore, these findings stress the need for adequate controlled studies to avoid misinterpretations of the data. 相似文献
7.
Flora S. Groothuizen Alexander Fish Maxim V. Petoukhov Annet Reumer Laura Manelyte Herrie H. K. Winterwerp Martin G. Marinus Joyce H. G. Lebbink Dmitri I. Svergun Peter Friedhoff Titia K. Sixma 《Nucleic acids research》2013,41(17):8166-8181
The process of DNA mismatch repair is initiated when MutS recognizes mismatched DNA bases and starts the repair cascade. The Escherichia coli MutS protein exists in an equilibrium between dimers and tetramers, which has compromised biophysical analysis. To uncouple these states, we have generated stable dimers and tetramers, respectively. These proteins allowed kinetic analysis of DNA recognition and structural analysis of the full-length protein by X-ray crystallography and small angle X-ray scattering. Our structural data reveal that the tetramerization domains are flexible with respect to the body of the protein, resulting in mostly extended structures. Tetrameric MutS has a slow dissociation from DNA, which can be due to occasional bending over and binding DNA in its two binding sites. In contrast, the dimer dissociation is faster, primarily dependent on a combination of the type of mismatch and the flanking sequence. In the presence of ATP, we could distinguish two kinetic groups: DNA sequences where MutS forms sliding clamps and those where sliding clamps are not formed efficiently. Interestingly, this inability to undergo a conformational change rather than mismatch affinity is correlated with mismatch repair. 相似文献
8.
9.
Manon R. Haverkate Mirjam J. D. Dautzenberg Tjaco J. M. Ossewaarde Anneke van der Zee Jan G. den Hollander Annet Troelstra Marc J. M. Bonten Martin C. J. Bootsma 《PloS one》2015,10(10)
During a large hospital outbreak of OXA-48 producing bacteria, most K. pneumoniae
OXA-48 isolates were phenotypically resistant to meropenem or imipenem, whereas most E. coli
OXA-48 isolates were phenotypically susceptible to these antibiotics. In the absence of molecular gene-detection E. coli
OXA-48 could remain undetected, facilitating cross-transmission and horizontal gene transfer of bla
OXA-48. Based on 868 longitudinal molecular microbiological screening results from patients carrying K. pneumoniae
OXA-48 (n = 24), E. coli
OXA-48 (n = 17), or both (n = 40) and mathematical modelling we determined mean durations of colonisation (278 and 225 days for K. pneumoniae
OXA-48 and E. coli
OXA-48, respectively), and horizontal gene transfer rates (0.0091/day from K. pneumoniae to E. coli and 0.0015/day vice versa). Based on these findings the maximum effect of horizontal gene transfer of bla
OXA-48 originating from E. coli
OXA-48 on the basic reproduction number (R
0) is 1.9%, and it is, therefore, unlikely that phenotypically susceptible E. coli
OXA-48 will contribute significantly to the spread of bla
OXA-48. 相似文献
10.
Roodenburg AJ Schlatmann A Dötsch-Klerk M Daamen R Dong J Guarro M Stergiou M Sayed N Ronoh E Jansen L Seidell JC 《PloS one》2011,6(2):e14721