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71.
Rapid Cycling of Organic Nitrogen in Taiga Forest Ecosystems 总被引:8,自引:0,他引:8
ABSTRACT
We examined the dynamics of organic nitrogen (N) turnover in situ across a primary successional sequence in interior Alaska,
USA, in an attempt to understand the magnitude of these fluxes in cold, seasonally frozen soils. Through a combination of
soil extraction procedures and measurements of 13C-enriched CO2 efflux from soils amended in the field with 13C-labeled amino acids, we were able to trace the fate of this N form. Amino acid turnover in situ at soil temperatures of
10°C or below show that amino acids represent a highly dynamic soil N pool with turnover times of approximately 3–6 h. The
rapid turnover of free amino acids is associated with high soil proteolytic activity, which in turn is tightly correlated
with soil protein concentration. Moreover, these estimates of soil amino acid turnover in the field correspond well with measurements
of amino acid turnover under equivalent temperatures in the laboratory. The gross flux of amino acid-N over the growing season
greatly exceeded the annual vegetation N requirement, suggesting that microbial biomass represent a significant sink for this
organic N. Depending on the strength of this sink, N flow via free soil amino acids can potentially account for the entire
N demand of vegetation in the absence of net N mineralization. These relationships underscore the important biogeochemical
role of labile DON fractions in high-latitude forest ecosystems. 相似文献
72.
Effects of forest clear-cutting on the carbon and nitrogen fluxes through podzolic soil horizons 总被引:8,自引:0,他引:8
Effects of clear-cutting on the dissolved fluxes of organic C (DOC), organic N (DON), NO3
– and NH4
+ through surface soil horizons were studied in a Norway spruce dominated mixed boreal forest in eastern Finland. Bulk deposition, total throughfall and soil water from below the organic (including understorey vegetation and, after clear-cutting, also logging residues), eluvial and illuvial horizons were sampled weekly from 1993 to 1999. Clear-cutting was carried out in September 1996. The removal of the tree canopy decreased the deposition of DOC and DON to the forest floor and increased that of NH4
+ and NO3
– but did not affect the deposition of total N (DTN, <3 kg ha–1 a–1). The leaching of DOC and DON from the organic horizon increased over twofold after clear-cutting (fluxes were on an average 168 kg C and 3.3 kg N ha–1 a–1), but the increased outputs were effectively retained in the surface mineral soil horizons. Inorganic N deposition was mainly retained by the logging residues and organic horizon indicating microbial immobilization. Increased NO3
– formation reflected as elevated concentrations in the percolate from below the mineral soil horizons were observed especially in the third year after clear-cutting. However, the changes were small and the increased leaching of DTN from below the illuvial horizon remained small (<0.4 kg ha–1 a–1) and mainly DON. Effects of clear-cutting on the transport of C and N to surface waters will probably be negligible. 相似文献
73.
Impacts of drinking water pretreatments on the formation of nitrogenous disinfection by-products 总被引:5,自引:0,他引:5
The formation of disinfection by-products (DBPs), including both nitrogenous DBPs (N-DBPs) and carbonaceous DBPs (C-DBPs), was investigated by analyzing chlorinated water samples following the application of three pretreatment processes: (i) powdered activated carbon (PAC) adsorption; (ii) KMnO(4) oxidation and (iii) biological contact oxidation (BCO), coupled with conventional water treatment processes. PAC adsorption can remove effectively the precursors of chloroform (42.7%), dichloroacetonitrile (28.6%), dichloroacetamide (DCAcAm) (27.2%) and trichloronitromethane (35.7%), which were higher than that pretreated by KMnO(4) oxidation and/or BCO process. The removal efficiency of dissolved organic carbon by BCO process (76.5%)--was superior to that by PAC adsorption (69.9%) and KMnO(4) oxidation (61.4%). However, BCO increased the dissolved organic nitrogen (DON) concentration which caused more N-DBPs to be formed during subsequent chlorination. Soluble microbial products including numerous DON compounds were produced in the BCO process and were observed to play an essential role in the formation of DCAcAm in particular. 相似文献
74.
Glutamine is an abundant amino acid that plays pivotal roles in cell growth, cell metabolism, and neurotransmission. Dysregulation of glutamine-using pathways has been associated with pathological conditions such as cancer and neurodegenerative diseases. 6-Diazo-5-oxo-l-norleucine (DON) is a reactive glutamine analog that inhibits enzymes affecting glutamine metabolism such as glutaminase, 2-N-amidotransferase, l-asparaginase, and several enzymes involved in pyrimidine and purine de novo synthesis. As a result, DON is actively used in preclinical models of cancer and neurodegenerative disease. Moreover, there have been several clinical trials using DON to treat a variety of cancers. Considerations of dose and exposure are especially important with DON treatment due to its narrow therapeutic window and significant side effects. Consequently, a robust quantification bioassay is of interest. DON is a polar unstable molecule that has made quantification challenging. Here we report on the characterization of a bioanalytical method to quantify DON in tissue samples involving DON derivatization with 3 N HCl in butanol. The derivatized product is lipophilic and stable. Detection of this analyte by mass spectrometry is fast and specific and can be used to quantify DON in plasma and brain tissue with a limit of detection at the low nanomolar level. 相似文献
75.
Guangfei Tang Ahai Chen Dawood H. Dawood Jingting Liang Yun Chen Zhonghua Ma 《Molecular Plant Pathology》2020,21(2):173-187
Deoxynivalenol (DON) is an important trichothecene mycotoxin produced by the cereal pathogen Fusarium graminearum. DON is synthesized in organized endoplasmic reticulum structures called toxisomes. However, the mechanism for toxisome formation and the components of toxisomes are not yet fully understood. In a previous study, we found that myosin I (FgMyo1)-actin cytoskeleton participated in toxisome formation. In the current study, we identified two new components of toxisomes, the actin capping proteins (CAPs) FgCapA and FgCapB. These two CAPs form a heterodimer in F. graminearum, and physically interact with FgMyo1 and Tri1. The deletion mutants ΔFgcapA and ΔFgcapB and the double deletion mutant ΔΔFgcapA/B dramatically reduced hyphal growth, asexual and sexual reproduction and endocytosis. More importantly, the deletion mutants markedly disrupted toxisome formation and DON production, and attenuated virulence in planta. Collectively, these results suggest that the actin CAPs are associated with toxisome formation and contribute to the virulence and development of F. graminearum. 相似文献
76.
The Nanjing Declaration on Nitrogen Management, signed in Nanjing in October 2004, calls for national governments to optimize
N management by several strategies including assessment of N cycles. Here we develop a first N budget for New Zealand (267,000 km2), at both national and regional scales. The national inputs are estimated to be 36.5 kg/ha, mainly from biological N fixation,
but also increasingly from fertilizer application and atmospheric deposition. The outputs are estimated at 40.5 kg/ha. Biological
N fixation from legumes in pasture was the most important input in most regions. Exceptions were Auckland, with a large urban
population, and the West Coast of the South Island, with large tracts of rain forest. Outputs were distributed in the order
leaching > ammonia volatilisation > erosion = produce = denitrification. These outputs are very different from global averages
because of the large numbers of grazing animals on pasture. A large loss occurs between the subsoil and the oceans, and further
research is needed to identify these pathways. Riverine export of N was generally well correlated with inputs. 相似文献
77.
The PKR regulatory subunit of protein kinase A (PKA) is involved in the regulation of growth,sexual and asexual development,and pathogenesis in Fusarium graminearum
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Chaoqun Li Yonghui Zhang Huan Wang Lingfeng Chen Ju Zhang Manli Sun Jin‐Rong Xu Chenfang Wang 《Molecular Plant Pathology》2018,19(4):909-921
Fusarium graminearum is a causal agent of wheat scab disease and a producer of deoxynivalenol (DON) mycotoxins. Treatment with exogenous cyclic adenosine monophosphate (cAMP) increases its DON production. In this study, to better understand the role of the cAMP–protein kinase A (PKA) pathway in F. graminearum, we functionally characterized the PKR gene encoding the regulatory subunit of PKA. Mutants deleted of PKR were viable, but showed severe defects in growth, conidiation and plant infection. The pkr mutant produced compact colonies with shorter aerial hyphae with an increased number of nuclei in hyphal compartments. Mutant conidia were morphologically abnormal and appeared to undergo rapid autophagy‐related cell death. The pkr mutant showed blocked perithecium development, but increased DON production. It had a disease index of less than unity and failed to spread to neighbouring spikelets. The mutant was unstable and spontaneous suppressors with a faster growth rate were often produced on older cultures. A total of 67 suppressor strains that grew faster than the original mutant were isolated. Three showed a similar growth rate and colony morphology to the wild‐type, but were still defective in conidiation. Sequencing analysis with 18 candidate PKA‐related genes in three representative suppressor strains identified mutations only in the CPK1 catalytic subunit gene. Further characterization showed that 10 of the other 64 suppressor strains also had mutations in CPK1. Overall, these results showed that PKR is important for the regulation of hyphal growth, reproduction, pathogenesis and DON production, and mutations in CPK1 are partially suppressive to the deletion of PKR in F. graminearum. 相似文献
78.
Weiwei Dai Sadie K. Dierschke Allyson L. Toro Michael D. Dennis 《生物化学与生物物理学报:疾病的分子基础》2018,1864(12):3568-3576
The incidence of type 2 diabetes, the most common cause of diabetic retinopathy (DR), is rapidly on the rise in developed countries due to overconsumption of calorie rich diets. Using an animal model of diet-induced obesity/pre-diabetes, we evaluated the impact of a diet high in saturated fat (HFD) on O-GlcNAcylation of retinal proteins, as dysregulated O-GlcNAcylation contributes to diabetic complications and evidence supports a role in DR. Protein O-GlcNAcylation was increased in the retina of mice fed a HFD as compared to littermates receiving control chow. Similarly, O-GlcNAcylation was elevated in retinal Müller cells in culture exposed to the saturated fatty acid palmitate or the ceramide analog Cer6. One potential mechanism responsible for elevated O-GlcNAcylation is increased flux through the hexosamine biosynthetic pathway (HBP). Indeed, inhibition of the pathway's rate-limiting enzyme glutamine-fructose-6-phosphate amidotransferase (GFAT) prevented Cer6-induced O-GlcNAcylation. Importantly, expression of the mRNA encoding GFAT2, but not GFAT1 was elevated in both the retina of mice fed a HFD and in retinal cells in culture exposed to palmitate or Cer6. Notably, expression of nuclear receptor subfamily 4 group A member 1 (NR4A1) was increased in the retina of mice fed a HFD and NR4A1 expression was sufficient to promote GFAT2 mRNA expression and O-GlcNAcylation in retinal cells in culture. Whereas palmitate or Cer6 addition to culture medium enhanced NR4A1 and GFAT2 expression, chemical inhibition of NR4A1 transactivation repressed Cer6-induced GFAT2 mRNA expression. Overall, the results support a model wherein HFD increases retinal protein O-GlcNAcylation by promoting NR4A1-dependent GFAT2 expression. 相似文献
79.
Quantitative trait loci associated with resistance to Fusarium head blight and kernel discoloration in barley 总被引:13,自引:5,他引:8
R. C. de la Pena K. P. Smith F. Capettini G. J. Muehlbauer M. Gallo-Meagher R. Dill-Macky D. A. Somers D. C. Rasmusson 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1999,99(3-4):561-569
Resistance to Fusarium head blight (FHB), deoxynivalenol (DON) accumulation, and kernel discoloration (KD) in barley are difficult
traits to introgress into elite varieties because current screening methods are laborious and disease levels are strongly
influenced by environment. To improve breeding strategies directed toward enhancing these traits, we identified genomic regions
containing quantitative trait loci (QTLs) associated with resistance to FHB, DON accumulation, and KD in a breeding population
of F4:7 lines using restriction fragment length polymorphic (RFLP) markers. We evaluated 101 F4:7 lines, derived from a cross between the cultivar Chevron and an elite breeding line, M69, for each of the traits in three
or four environments. We used 94 previously mapped RFLP markers to create a linkage map. Using composite interval mapping,
we identified 10, 11, and 4 QTLs associated with resistance to FHB, DON accumulation, and KD, respectively. Markers flanking
these QTLs should be useful for introgressing resistance to FHB, DON accumulation, and KD into elite barley cultivars.
Received: 8 November 1998 / Accepted: 8 January 1999 相似文献
80.
Yu Umezawa Toshihiro Miyajima Yasuaki Tanaka Isao Koike Takeshi Hayashibara 《Journal of phycology》2007,43(3):437-448
The utility of δ15N measurements in Padina australis Hauck as a probe for its external nitrogen (N) sources was tested by monitoring the bulk values of chemical components [δ15N, δ13C, and N and carbon (C) contents] and their internal distributions during a 12 d incubation in a controlled environment. Under the saturated conditions of isotopically heavier nitrate than that of original algal tissue, the bulk δ15N in P. australis was enriched, but less than what was predicted from a simple mixing model, signaling possible isotopic discrimination during N assimilation and subsequent N efflux from the cells. The enhanced N content (%), which occurred simultaneously with this δ15N shift, was a useful signal indicating this phenomenon. Bulk δ15N was enriched, especially around the meristem, in tissues growing under conditions of higher irradiance and temperature, probably due in part to dissolved organic nitrogen (DON) excretion. The δ13C enhancement in bulk algal tissues, also associated with high photosynthetic activity, may be an additional signal indicating this unbalanced internal δ15N distribution. However, in summer and winter environmental conditions with periodic nitrate supplies simulating typical fringing reef waters, the difference in measured algal bulk δ15N from theoretical predictions was within ±1.0‰. This difference is very small compared with the variation in δ15N in possible N sources in coastal areas. In the field, therefore, δ15N in Padina can be used effectively to trace N sources in both space and time after determining algal N content and δ13C to determine whether large alterations occur in algal δ15N. 相似文献