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141.
Seth G. Pritchard Hugo H. Rogers Micheal A. Davis Edzard Van Santen Stephen A. Prior William H. Schlesinger 《Global Change Biology》2001,7(7):829-837
Root dynamics are important for plant, ecosystem and global carbon cycling. Changes in root dynamics caused by rising atmospheric CO2 not only have the potential to moderate further CO2 increases, but will likely affect forest function. We used FACE (Free‐Air CO2 Enrichment) to expose three 30‐m diameter plots in a 13‐year‐old loblolly pine (Pinus taeda) forest to elevated (ambient + 200 µL L?1) atmospheric CO2. Three identical fully instrumented plots were implemented as controls (ambient air only). We quantified root dynamics from October 1998 to October 1999 using minirhizotrons. In spite of 16% greater root lengths and 24% more roots per minirhizotron tube, the effects of elevated atmospheric CO2 on root lengths and numbers were not statistically significant. Similarly, production and mortality were also unaffected by the CO2 treatment, even though annual root production and mortality were 26% and 46% greater in elevated compared to ambient CO2 plots. Average diameters of live roots present at the shallowest soil depth were, however, significantly enhanced in CO2‐enriched plots. Mortality decreased with increasing soil depth and the slopes of linear regression lines (mortality vs. depth) differed between elevated and ambient CO2 treatments, reflecting the significant CO2 by depth interaction. Relative root turnover (root flux/live root pool) was unchanged by exposure to elevated atmospheric CO2. Results from this study suggest modest, if any, increases in ecosystem‐level root productivity in CO2‐enriched environments. 相似文献
142.
Wu Y Zhan L Ai Y Hannigan M Gaestel M Huang CK Madri JA 《Biochemical and biophysical research communications》2007,358(1):170-175
In neutrophils, the major substrate of MAPKAPK2 (MK2) is an F-actin binding protein LSP1. Studies using mutants of the two potential Serine phosphorylation sites in LSP1 C-terminal F-actin binding region indicated that the major phosphorylation site for MK2 is Ser243 in murine neutrophils (Ser252 in humans). Human phosphoLSP1 antibodies that recognize phosphoSer252 site were prepared and revealed fMLP-induced neutrophil LSP1 phosphorylation. The phosphorylation was inhibited by p38 MAPK (upstream kinase for MK2) inhibitor SB203580. The antibodies also detect LSP1 phosphorylation in murine neutrophils. Immunostaining revealed that in WT murine neutrophils phosphoLSP1 was localized in F-actin enriched lamellipodia and oriented toward the fMLP gradient while non-phosphoLSP1 failed to colocalize with F-actin. In suspension, WT neutrophils exhibited persistent F-actin polarization following fMLP stimulation, while MK2(-/-) neutrophils exhibited transient F-actin polarization. These studies suggest that MK2-regulated LSP1 phosphorylation is involved in stabilization of F-actin polarization during neutrophil chemotaxis. 相似文献
143.
Protein kinase C as a stress sensor 总被引:1,自引:0,他引:1
While there are many reviews which examine the group of proteins known as protein kinase C (PKC), the focus of this article is to examine the cellular roles of two PKCs that are important for stress responses in neurological tissues (PKC gamma and epsilon) and in cardiac tissues (PKC epsilon). These two kinases, in particular, seem to have overlapping functions and interact with an identical target, connexin 43 (Cx43), a gap junction protein which is central to proper control of signals in both tissues. While PKC gamma and PKC epsilon both help protect neural tissue from ischemia, PKC epsilon is the primary PKC isoform responsible for responding to decreased oxygen, or ischemia, in the heart. Both do this through Cx43. It is clear that both PKC gamma and PKC epsilon are necessary for protection from ischemia. However, the importance of these kinases has been inferred from preconditioning experiments which demonstrate that brief periods of hypoxia protect neurological and cardiac tissues from future insults, and that this depends on the activation, translocation, or ability for PKC gamma and/or PKC epsilon to interact with distinct cellular targets, especially Cx43. This review summarizes the recent findings which define the roles of PKC gamma and PKC epsilon in cardiac and neurological functions and their relationships to ischemia/reperfusion injury. In addition, a biochemical comparison of PKC gamma and PKC epsilon and a proposed argument for why both forms are present in neurological tissue while only PKC epsilon is present in heart, are discussed. Finally, the biochemistry of PKCs and future directions for the field are discussed, in light of this new information. 相似文献
144.
Zhi Jiang Chen Micheal Negra Angela Levine Yvonne Ughrin Joel M. Levine 《Brain Cell Biology》2002,31(6-7):481 ppl=-495
Oligodendrocyte precursor cells (OPCs) are a newly recognized glial component of the adult central nervous system of unknown function. Antibodies against the NG2 chondroitin sulfate proteoglycan have been useful tools to identify these cells in intact tissue. Here we review studies that show that OPCs react to several types of experimentally induced brain injury. Injury stimulates OPCs to re-enter the cell cycle, divide, and accumulate at the site of damage. OPCs, together with microglia and astrocytes, form the glial scar. Glial scars are thought to inhibit or prevent axonal regeneration and reactive OPCs contribute to this inhibition by producing growth-inhibiting chondroitin sulfate proteoglycans, particularly NG2. In developing animals, NG2 is found in areas, such as the perinotochordal mesenchyme, that are avoided by growing motor and sensory axons. Within the developing CNS, NG2-expressing cells surround the developing optic chiasm and tract and separate it from the overlying diencephalon. Thus, NG2-expressing cells are well positioned to inhibit axonal growth from developing as well as regenerating neurons. 相似文献
145.
146.
John S. Thompson Reto Asmis Andrea A. Tapp Brandy Nelson Yanxia Chu Judith Glass Micheal Moneyhon Stephen A. Brown 《Apoptosis : an international journal on programmed cell death》2010,15(6):705-714
Ionizing radiation (IR) is a pro-oxidant that kills cells by both apoptotic and necrotic mechanisms. Pyrrolidine dithiocarbamate
(PDTC) is a thiol-containing compound that may act either as a pro- or anti-oxidant depending on the experimental conditions.
This study was designed to determine whether PDTC would reduce or enhance IR-induced cell death of freshly-isolated normal
mouse B6/129 spleen cells (NMSC). We determined the effect of increasing doses of IR, PDTC alone and PDTC followed by IR on
the viability of NMSC. Annexin V and propidium iodide (Annexin V/PI) staining demonstrated a dose and time-dependent relationship
in which PDTC enhanced the percentage of IR-induced apoptotic/necrotic NMSC. Trypan blue dye inclusion confirmed that a loss
of membrane integrity was occurring 1 h after incubation with PDTC plus IR. Reduction in the glutathione (GSH)/glutathione
disulfide (GSSG) ratio and GSH demonstrated that both IR (8.5 Gy) and PDTC acted as pro-oxidants, but their mechanisms of
action differed: In contrast to IR, which promoted p53 activation and caspase 3/7-mediated apoptosis, PDTC inhibited IR-induced
p53 and caspase 3/7 activity. However, PDTC increased H2O2 formation and necrosis, resulting in an overall increase in IR-induced cell death. Catalase prevented the PDTC-induced increase
in IR cytotoxicity implicating the generation of H2O2 as a major factor in this mechanism. These results demonstrate that in NMSC PDTC acts as pro-oxidant and enhances IR-induced
cell cytotoxicity by increasing H2O2formation and thiol oxidation. As such, they strongly suggest that the use of PDTC as an adjunct to reduce radiation toxicity
should be avoided. 相似文献
147.
Hyperaccumulated elements such as Ni may defend plants against some natural enemies whereas other enemies may circumvent this defense. The Ni hyperaccumulator Berkheya coddii Roessler (Asteraceae) is a host plant species for Chrysolina clathrata (Clark), which suffers no apparent harm by consuming its leaf tissue. Beetle specimens collected from B. coddii had a whole body Ni concentration of 260 μg/g dry weight, despite consuming leaf material containing 15 100 μg Ni/g. Two experiments were conducted with adults of this beetle species: a no-choice experiment and a choice experiment. In the no-choice experiment we offered beetles foliage of one of four species of Berkheya: B. coddii, B. rehmannii Thell. var. rogersiana Thell., B. echinacea (Harv.) O. Hoffm. ex Burtt Davey, and B. insignis (Harv.) Thell. The two former species are Ni hyperaccumulators (defined as having leaf Ni concentration > 1 000 μg/g) whereas the latter have low Ni levels (< 200 μg/g) in their leaves. Masses of beetles were monitored for 6 days. Choice experiments used growing stem tips from the same Berkheya species, placed into Petri dishes with five Chrysolina beetles in each, and the amount of feeding damage caused on each of the four species was recorded. Beetles in the no-choice experiment gained mass when offered B. coddii , maintained mass on leaves of the other Ni hyperaccumulator ( B. rehmannii var. rogersiana ), and lost mass when offered non-hyperaccumulator leaves. In the choice test, beetles strongly preferred B. coddii to other Berkheya species. We conclude that C. clathrata may be host-specific on B. coddii. 相似文献
148.
Micheal Trzoss Daniel C. Bensen Xiaoming Li Zhiyong Chen Thanh Lam Junhu Zhang Christopher J. Creighton Mark L. Cunningham Bryan Kwan Mark Stidham Kirk Nelson Vickie Brown-Driver Amanda Castellano Karen J. Shaw Felice C. Lightstone Sergio E. Wong Toan B. Nguyen John Finn Leslie W. Tari 《Bioorganic & medicinal chemistry letters》2013,23(5):1537-1543
The structurally related bacterial topoisomerases DNA gyrase (GyrB) and topoisomerase IV (ParE) have long been recognized as prime candidates for the development of broad spectrum antibacterial agents. However, GyrB/ParE targeting antibacterials with spectrum that encompasses robust Gram-negative pathogens have not yet been reported. Using structure-based inhibitor design, we optimized a novel pyrrolopyrimidine inhibitor series with potent, dual targeting activity against GyrB and ParE. Compounds were discovered with broad antibacterial spectrum, including activity against Pseudomonas aeruginosa, Acinetobacter baumannii and Escherichia coli. Herein we describe the SAR of the pyrrolopyrimidine series as it relates to key structural and electronic features necessary for Gram-negative antibacterial activity. 相似文献
149.
Mary J. Ortner Micheal J. Galvin Donald I. McRee Colin F. Chignell 《Journal of biochemical and biophysical methods》1981,5(3):157-167
Instrumentation has been developed which allows the monitoring of fluorescnece in erythrocyte ghost membranes before, during, and after exposure to microwave radiation. Using non-fluorescent, UV-transmitting transmitting fiber optic cables, excitation light of specific wavelengths was delivered to a stirred sample undergoing irradiation (2450 MHz, CW) within a fluid-filled, temperature-controlled waveguide. Fluorescence was collected using an identical cable and transferred through appropriate filters to standard detecting, amplification and recording devices. We have used the fluorescent probe, 1-anilino-8-naphthalene sulfonate (ANS)_to monitor the effect of mirowave radiation on the binding of calcium to erthrocyte ghosts. Microwave radiation at specific absorption rates of 10 and 200 mW/g had no effect on the binding of ANS to the membranes. Dose-responses curves also showed no influence of microwaves on calcium binding between 2.0 and 10.0 · 10?4 M. In addition, experiments studying fluorescence energy transfer between intrinsic tryptophan residues and membrane bound ANS showed that intermolecular distance between donor and acceptor are also unaffected by microwave radiation. We have thus shown that 2450 MHz microwve radition at the specific absorption rates studies rates used does not interfere with the binding of calcium to erythrocyte ghosts or alter intermolecular distances intrinsic molecules and bound ANS. 相似文献
150.
Udwary DW Gontang EA Jones AC Jones CS Schultz AW Winter JM Yang JY Beauchemin N Capson TL Clark BR Esquenazi E Eustáquio AS Freel K Gerwick L Gerwick WH Gonzalez D Liu WT Malloy KL Maloney KN Nett M Nunnery JK Penn K Prieto-Davo A Simmons TL Weitz S Wilson MC Tisa LS Dorrestein PC Moore BS 《Applied and environmental microbiology》2011,77(11):3617-3625
Bacteria of the genus Frankia are mycelium-forming actinomycetes that are found as nitrogen-fixing facultative symbionts of actinorhizal plants. Although soil-dwelling actinomycetes are well-known producers of bioactive compounds, the genus Frankia has largely gone uninvestigated for this potential. Bioinformatic analysis of the genome sequences of Frankia strains ACN14a, CcI3, and EAN1pec revealed an unexpected number of secondary metabolic biosynthesis gene clusters. Our analysis led to the identification of at least 65 biosynthetic gene clusters, the vast majority of which appear to be unique and for which products have not been observed or characterized. More than 25 secondary metabolite structures or structure fragments were predicted, and these are expected to include cyclic peptides, siderophores, pigments, signaling molecules, and specialized lipids. Outside the hopanoid gene locus, no cluster could be convincingly demonstrated to be responsible for the few secondary metabolites previously isolated from other Frankia strains. Few clusters were shared among the three species, demonstrating species-specific biosynthetic diversity. Proteomic analysis of Frankia sp. strains CcI3 and EAN1pec showed that significant and diverse secondary metabolic activity was expressed in laboratory cultures. In addition, several prominent signals in the mass range of peptide natural products were observed in Frankia sp. CcI3 by intact-cell matrix-assisted laser desorption-ionization mass spectrometry (MALDI-MS). This work supports the value of bioinformatic investigation in natural products biosynthesis using genomic information and presents a clear roadmap for natural products discovery in the Frankia genus. 相似文献