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991.
Trace gas flux and the influence of short-term soil water and temperature dynamics in Australian sheep grazed pastures of differing productivity 总被引:1,自引:0,他引:1
S. J. Livesley R. Kiese J. Graham C. J. Weston K. Butterbach-Bahl S. K. Arndt 《Plant and Soil》2008,309(1-2):89-103
Temperate pastures are often managed with P fertilizers and N2-fixing legumes to maintain and increase pasture productivity which may lead to greater nitrous oxide (N2O) emissions and reduced methane (CH4) uptake. However, the diel and inter-daily variation in N2O and CH4 flux in pastures is poorly understood, especially in relation to key environmental drivers. We investigated the effect of pasture productivity, rainfall, and changing soil moisture and temperature upon short-term soil N2O and CH4 flux dynamics during spring in sheep grazed pasture systems in southeastern Australia. N2O and CH4 flux was measured continuously in a High P (23 kg P ha?1 yr?1) and No P pasture treatment and in a sheep camp area in a Low P (4 kg P ha?1 yr?1) pasture for a four week period in spring 2005 using an automated trace gas system. Although pasture productivity was three-fold greater in the High P than No P treatment, mean CH4 uptake was similar (?6.3?±?SE 0.3 to ?8.6?±?0.4 μg C m?2 hr?1) as were mean N2O emissions (6.5 to 7.9?±?0.8 μg N m?2 hr?1), although N2O flux in the No P pasture did not respond to changing soil water conditions. N2O emissions were greatest in the Low P sheep camp (12.4 μg?±?1.1 N m?2 hr?1) where there were also net CH4 emissions of 5.2?±?0.5 μg C m?2 hr?1. There were significant, but weak, relationships between soil water and N2O emissions, but not between soil water and CH4 flux. The diel temperature cycle strongly influenced CH4 and N2O emissions, but this was often masked by the confounding covariate effects of changing soil water content. There were no consistently significant differences in soil mineral N or gross N transformation rates, however, measurements of substrate induced respiration (SIR) indicated that soil microbial processes in the highly productive pasture are more N limited than P limited after >20 years of P fertilizer addition. Increased productivity, through P fertilizer and legume management, did not significantly increase N2O emissions, or reduce CH4 uptake, during this 4 week measurement period, but the lack of an N2O response to rainfall in the No P pasture suggests this may be evident over a longer measurement period. This study also suggests that small compacted and nutrient enriched areas of grazed pastures may contribute greatly to the overall N2O and CH4 trace gas balance. 相似文献
992.
993.
M B Baru L G Mustaeva I V Vagenina E Y Gorbunova V V Cherskii 《The journal of peptide research》2001,57(3):193-202
We describe the noninvasive real-time pressure monitoring of Boc- and Fmoc-based peptide synthesis. Pressure was measured using a resistance strain gauge attached to the inlet of a continuous-flow reactor of variable volume. In the assembly of the 'difficult' polyalanine sequence, it was shown that pressure monitoring can reveal structural variations of the peptide-resin, e.g. the onset, development and termination of aggregation. This method provided washing minimization that favored substantial saving of solvents. The obtained results demonstrated the advantage of pressure monitoring over swellographic monitoring. 相似文献
994.
We have established a series of 20 colorectal cancer cell lines and performed cytogenetic and RFLP analyses to show that the
recurrent genetic abnormalities of chromosomes 1, 5, 17 and 18 associated with multistep tumorigenesis in colorectal cancer,
and frequently detected as recurrent abnormalities in primary tumours, are also retained in long-term established cell lines.
Earlier studies by us and other investigators showed that allelic losses of chromosomes 1 and 17 in primary colorectal cancers
predicted poorer survival for the patients (P = 0.03). We utilized the cell lines to identify specific chromosomal sites or gene(s) on chromosomes 1 and 17 which confer
more aggressive phenotype. Cytogenetic deletions of chromosome 1p were detected in 14 out of the 20 (70%) cell lines, whereas
allelic deletions for 1p using polymorphic markers were detected in 13 out of 18 (72%) informative cell lines for at least
one polymorphic marker. We have performed Northern blotting, immunohistochemical staining (p53 mRNA, protein) and RFLP analysis
using several probes including p53 and nm23. RFLP analysis using a total of seven polymorphic markers located on 17p and 17q
arms showed allelic losses aroundthe p53 locus in 16 out of the 20 cell lines (80%), four of which were losses of thep53 locus itself. In addition, seven cell lines (out of nine informative cases) also showed losses of thenm23 gene, four with concurrent losses of thep53 locus, while the remaining three were homozygous. In addition, five out of seven cell lines withnm23 deletions were derived from hepatic metastatic tumours, and one cell line was obtained from recurrent tumour. A comparison
between allelic deletions of 1p and functional loss ofnm23 gene revealed a close association between these two events in cell lines derived from hepatic metastasis. Following immunohistochemical
staining, nine out of the twenty cell lines showed high levels (25–80%) of mutant p53, four showed intermediate levels (>20%),
and seven had undetectable levels of the protein. Of these seven, four showed complete absence of mRNA. Of the remaining three
cell lines one showed aberrant mRNA due to germline rearrangement of thep53 gene, whereas in two cell lines normal levels of mRNA were present. Nineteen of the 20 cell lines had normal germline configurations
for thep53 gene, while one showed a rearrangement. These data suggest that functional loss ofp53 andnm23 genes accomplished by a variety of mechanisms may be associated with poor prognosis and survival. In addition, concurrent
deletions of chromosome regions 17p, 17q and 1p were closely associated with high-stage hepatic metastatic disease. These
cell lines with well-characterized genetic alterations and known clinical history provide an invaluable source of material
for various biological and clinical studies relating to multistep colorectal tumorigenesis. 相似文献
995.
Future uses of pollen analysis must include plant macrofossils 总被引:8,自引:0,他引:8
996.
Polymyxin B (PMB), a cyclic cationic peptide antibiotic, despite its severe side effects continues to occupy a premiere position for treating endotoxicosis. Its mode of neutralization of endotoxin has remained elusive for the last three decades. Several synthetic peptide mimics of PMB, capable of binding endotoxin, have been made. However, the binding ability alone appears to be a deceptive indicator of endotoxin neutralizing activity as molecules with similar binding propensities could either sequester or opsonize the toxin. Hence identification of additional physical parameters which describe adequately the outcome of PMB-endotoxin interaction become imperative. Surface plasmon resonance (SPR) studies reported here show that several mimics of PMB despite exhibiting lipopolysaccharide binding affinities comparable with it but, unlike it, do not sequester the endotoxin. These studies thus provide a striking illustration of the difference in the behavior of PMB, vis a vis its mimics toward the endotoxin lamellae, and define further, in chemical terms, mechanism of the action of PMB and allow us to posit that the design of molecules as effective antidotes for sepsis should incorporate the ability to sequester endotoxin specifically. 相似文献
997.
998.
A modification of the trap assay (Woodard et al., 1989) was used to evaluate the response of Drosophila melanogaster (Meigen) to food media containing menthol. Dose-response curves for flies to mentholic foods were produced for flies that had been pre-exposed to menthol, during development and adult life, and flies that had not been exposed to menthol before the assay. Mentholic food media were less attractive to Drosophila than plain food medium. Rearing flies on a medium containing menthol reduced their aversion to some concentrations of menthol. The rearing effect was not simply due to lowered general activity levels resulting from developing in a medium containing menthol. There was a threshold concentration of menthol in the rearing medium below which we found no induced behavioural change. 相似文献
999.
1000.
Sigrid C Roberts Jerry Scott Judith E Gasteier Yuqui Jiang Benjamin Brooks Armando Jardim Nicola S Carter Olle Heby Buddy Ullman 《The Journal of biological chemistry》2002,277(8):5902-5909
The polyamine biosynthetic enzyme, S-adenosylmethionine decarboxylase (ADOMETDC) has been advanced as a potential target for antiparasitic chemotherapy. To investigate the importance of this protein in a model parasite, the gene encoding ADOMETDC has been cloned and sequenced from Leishmania donovani. The Delta adometdc null mutants were created in the insect vector form of the parasite by double targeted gene replacement. The Delta adometdc strains were incapable of growth in medium without polyamines; however, auxotrophy could be rescued by spermidine but not by putrescine, spermine, or methylthioadenosine. Incubation of Delta adometdc parasites in medium lacking polyamines resulted in a drastic increase of putrescine and glutathione levels with a concomitant decrease in the amounts of spermidine and the spermidine-containing thiol trypanothione. Parasites transfected with an episomal ADOMETDC construct were created in both wild type and Delta adometdc parasites. ADOMETDC overexpression abrogated polyamine auxotrophy in the Delta adometdc L. donovani. In addition, ADOMETDC overproduction in wild type parasites alleviated the toxic effects of 5'-(((Z)-4-amino-2-butenyl)methylamino)-5'-deoxyadenosine (MDL 73811), but not pentamidine, berenil, or methylglyoxyl bis(guanylhydrazone), all inhibitors of ADOMETDC activities in vitro. The molecular, biochemical, and genetic characterization of ADOMETDC establishes that it is essential in L. donovani promastigotes and a potential target for therapeutic validation. 相似文献