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11.
Fine root turnover in forest ecosystems in relation to quantity and form of nitrogen availability: a comparison of two methods 总被引:20,自引:0,他引:20
John D. Aber Jerry M. Melillo Knute J. Nadelhoffer Charles A. McClaugherty John Pastor 《Oecologia》1985,66(3):317-321
Summary Two methods of estimating fine root production and turnover are compared for 13 forest ecosystems exhibiting a wide range in form (NH4
+ vs. NO3
-) and quantity of available nitrogen. The two methods are by comparison of seasonal maxima and minima in biomess and by nitrogen budgeting. Both methods give similar results for stands with low rates of nitrification. The budgeting method predicts higher fine root turnover and productivity than the max-min method for systems with significant rates of nitrification. 相似文献
12.
Genetic analysis and molecular cloning of the Escherichia coli ruv gene 总被引:22,自引:0,他引:22
Claire E. Shurvinton Robert G. Lloyd Fiona E. Benson Paul V. Attfield 《Molecular & general genetics : MGG》1984,194(1-2):322-329
Summary The genetic organisation of the ruv gene, a component of the SOS system for DNA repair and recombination in Escherichia coli, was investigated. New point mutations as well as insertions and deletions were generated using transposon Tn10 inserted in eda as a linked marker for site specific mutagenesis, or directly as a mutagen. The mutations were ordered with respect to one another and previously isolated ruv alleles by means of transductional crosses. The direction of chromosome mobilization from ruv:: Mud(ApR
lac)strains carrying F42lac
+ established that ruv is transcribed in a counterclockwise direction. Recombinant phages able to restore UV resistance to ruv mutants were identified, and the ruv
+ region was subcloned into a low copy number plasmid. The ruv
+ plasmid was able to correct the extreme radiation sensitivity and recombination deficiency of ruv recBC sbcB strains. 相似文献
13.
Peter W. Goodenough Peter J. Kilshaw Fiona McEwan A. Jane Owen 《Bioscience reports》1986,6(8):759-766
The proteinases fromCarica papaya include papain, isoenzymes of chymopapain and two proteinases A and B distinguished by their unusually high pI. The identity of one of the most basic proteinases has been questioned. The present report describes the preparation and characterisation of two monoclonal antibodies that react specifically with papaya proteinases A and B respectively and a third that identifies a common structural feature found in papain and proteinase A. 相似文献
14.
The renal corpuscle of hibernating and non-hibernating Testudo graeca was studied by means of light and electron microscopy. Renal corpuscles are small and have a glomerular architecture similar to that found in other vertebrates with a limited glomerular filtration rate. In hibernating animals, unlike non-hibernating, some morphological changes took place. The cells of the renal corpuscle were densely packed, podocytes and parietal cells showed a marked cytoplasmic vacuolization, there was a highly developed capillary basement membrane and the endothelial and mesangial cells showed abundant dense granules. These morphological features apparently correspond to a vacuolar degeneration. They may also be the morphological basis of the decrease in the glomerular filtration rate observed during this period. 相似文献
15.
The glutamine analog, 6-diazo-5-oxo-l-norleucine (DON), a glycoconjugate inhibitor, was used to probe the relationships between myocardial secretion of extracellular matrix and endothelial differentiation and formation of cushion mesenchyme (primordia of AV values). When DON was given to stage 12 chick embryos maintained in shell-less culture, the myocardial secretion gradient of glucose- and sulfate-labeled matrix was blocked. Concomitantly, the endothelium failed to complete activation but continued to divide and incorporate thymidine. By varying DON concentration, two distinct phases of endothelial differentiation were identified: the first (labile to 0.5 μg) involved hypertrophy, the second (labile to 0.25 μg) acquisition of migratory appendages with resultant mesenchyme formation. Glucosamine + DON (but not inosine, glucose, or glutamine) restored the matrical secretion gradient and to varying degrees both phases of endothelial activation. Endothelia totally suppressed from forming mesenchyme in situ acquired this capacity when explanted into three-dimensional collagen gel culture. The capacity was enhanced by glucosamine given in situ as an inhibitory override, dependent upon serum concentration, inhibited by heat-inactivated serum or by adding DON to the medium, but unaffected by hyaluronate. These results were compared to those obtained by co-culturing endothelium and myocardium and discussed in terms of the hypothesis that cushion mesenchyme formation results from an epithelial interaction mediated by glycoconjugates. 相似文献
16.
Hemming Fiona J. Begeot Martine Dubois Maurice P. Dubois Paul M. 《Cell and tissue research》1983,234(2):427-437
Corticotropes of rat fetuses aged 16, 18 and 21 days were localized by the indirect antibody-enzyme method on semithin sections of the pituitary. The development of the ultrastructure of these cells was observed on consecutive ultrathin sections. In comparison with previous data our present results show that identification of a fetal cell type cannot be based entirely on morphological criteria. The structural peculiarities of corticotropes obtained from studies in vivo are compared with those observed in cells maintained in vitro. 相似文献
17.
Molecular and functional analysis of the ruv region of Escherichia coli K-12 reveals three genes involved in DNA repair and recombination 总被引:14,自引:0,他引:14
Gary J. Sharples Fiona E. Benson Graham T. Illing Robert G. Lloyd 《Molecular & general genetics : MGG》1990,221(2):219-226
Summary Recombinant plasmids carrying ruvA, ruvB, or both were constructed and used to investigate the genetic defects in a collection of UV-sensitive ruv mutants. The results revealed that efficient survival of UV-irradiated cells depends on both ruvA and ruvB, and on a third gene, ruvC, located upstream of the ruvAB operon. Southern blotting analysis was used to locate insertions in ruv and to examine putative deletion mutants. Two Tn10 insertions were located to the region encoding ruvA. Since these insertions caused a deficiency in the activities of both ruvA and ruvB, we concluded that they must exert a polar effect on ruvB. Two putative ruv deletion mutants were shown to be the result of deletion-inversion events mediated during imprecise excision of Tn10. The relevant inversion breakpoints in these mutants were located to ruvA and ruvC. 相似文献
18.
Incubation of human bloodstream neutrophils with 50 u/ml recombinant granulocyte-macrophage colony-stimulating factor (rGM-CSF) primed the respiratory burst (as assessed by fMet-Leu-Phe stimulated luminol-dependent chemiluminescence) and resulted in a rapid (within 15 min) upregulation of expression of CD11b and CD18 (as measured by FACS analysis). This rapid priming and modulation of receptor expression was not inhibited by cycloheximide and hence appeared to be independent ofde novo protein biosynthesis. When neutrophils were incubated for up to 5 h in culture, the fluorescence distributions of CD11b and CD18 declined indicating the loss of expression of these receptors as the neutrophils aged, but in rGM-CSF treated suspensions receptor expression was maintained. When neutrophils were incubated in the presence of cycloheximide, they progressively lost their ability to generate reactive oxidants in response to fMet-Leu-Phe so that by 5 h incubation with this inhibitor they could only generate about 25% of the oxidative response stimulated in untreated cells, and the expression of CD16 and CD18 was grossly impaired. Similar effects were observed in rGM-CSF treated suspensions except that cycloheximide required longer incubation times (typically 4–5 h) before impairment of function or receptor expression occurred. These data show thatde novo protein biosynthesis is required for both the maintenance of neutrophil function and also for the continued expression of some plasma membrane receptors.Abbreviations fMet-Leu-Phe
N-formylmethionyl-Leucyl-Phenylalanine
- rGM-CSF
recombinant granulocyte-macrophage colony-stimulating factor
- FITC
fluorescein isothiocyanate conjugate
- Luminol
5-amino-2,3-dihydrophthalazine-1,4-dione 相似文献
19.
Final instar Persectania ewingii (Westwood) (Lepidoptera: Noctuidae) were fed seedling Triticum aestivum L. for 2 days to determine the approximate digestibility of the cell wall and cell content fractions. Cell wall content was estimated using a micro-analytical neutral detergent fibre technique. Approximate digestibilites of neutral detergent fibre, neutral detergent solubles and dry matter were calculated for individuals and pooled samples. P. ewingii larvae digested a small but significant proportion of the fibre ingested (13–21%), higher than that previously reported for herbivorous insects. The micro-analytical and previously used macro-analytical techniques produced similar estimates of digestibility although both techniques have inherent shortcomings, the latter requiring the pooling of samplex and the former limiting the number of replicates during chemical analysis. Differences in the amount of larval frass collected during the feeding trial (corrected for consumption) explained much of the variation in digestibility values, while there were no effects of larval mass, overall consumption and total frass produced on digestibility estimates. These results confirm that plant cell contents are the major source of nutrients to larval Lepidoptera although there is some chemical disruption of the plant cell wall. 相似文献
20.
Eitel Pastor Cristina Otero Antonio Ballesteros 《Biocatalysis and Biotransformation》1995,12(2):147-157
Mixtures of 1(3)-monostearin and distearin were prepared by direct esterification of glycerol with stearic acid or transesterification using ethyl stearate as acyl donor in the presence of Candida antarctica lipase (Novozym 435) using a variety of solvents of differing polarity. In all cases, the transesterification resulted in higher product yields. In n-heptane as reaction medium the addition of water (3%) was essential for high product yields, with mono- and distearin being produced in almost equal amounts. Using more polar solvents as reaction media, such as acetonitrile or acetone, again the highest yields were obtained in the transesterification mode; employing these solvents the reactions were much more selective towards the formation of monostearin. 相似文献