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1.

Background and Aims

Resin ducts (RDs) are features present in most conifer species as defence structures against pests and pathogens; however, little is known about RD expression in trees following fire injury. This study investigates changes in RD size and density in fire scars of Douglas fir (Pseudotsuga menziesii) and western larch (Larix occidentalis) as a means to evaluate the ecophysiological significance of traumatic resinosis for tree defence and survival.

Methods

Transverse and tangential microsections were prepared for light microscopy and image analysis in order to analyse axial and radial RDs, respectively. Epithelial cells of RDs and fusiform rays associated with radial RDs were also examined. RDs were compared between normal xylem and wound xylem at four different section heights along the fire-injured stem.

Key Results

Following fire injury, P. menziesii axial RDs narrowed by 38–43 % in the first year after injury, and the magnitude of this change increased with stem height. Larix occidentalis axial RDs widened by 46–50 % in the second year after injury. Radial RDs were of equivalent size in P. menziesii, but widened by 162–214 % in L. occidentalis. Fusiform rays were larger following fire injury, by 4–14 % in P. menziesii and by 23–38 % in L. occidentalis. Furthermore, axial RD density increased in both species due to the formation of tangential rows of traumatic RDs, especially in the first and second years after injury. However, radial RD density did not change significantly.

Conclusions

These results highlight traumatic resinosis as a species-specific response. Pseudotsuga menziesii produce RDs of equivalent or reduced size, whereas L. occidentalis produce wider RDs in both the axial and radial duct system, thereby increasing resin biosynthesis and accumulation within the whole tree. Larix occidentalis thus appears to allocate more energy to defence than P. menziesii.  相似文献   
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A Drosophila-related expressed sequence tag (DRES) with sequence similarity to the peanut gene has previously been localized to human chromosome 22q11. We have isolated the cDNA corresponding to this DRES and show that it is a novel member of the family of septin genes, which encode proteins with GTPase activity thought to interact during cytokinesis. The predicted protein has P-loop nucleotide binding and GTPase motifs. The gene, which we call PNUTL1, maps to the region of 22q11.2 frequently deleted in DiGeorge and velo-cardio-facial syndromes and is particularly highly expressed in the brain. The mouse homologue, Pnutl1, maps to MMU16 adding to the growing number of genes from the DiGeorge syndrome region that map to this chromosome.  相似文献   
5.
Recently it was reported that limb joint surface areas scale positively allometrically with body weight in anthropoid primates. This was attributed to the biomechanics of weight bearing: larger animals must require relatively larger joint surfaces to withstand relatively greater weight-related stresses on the joints. Our data on humeral and femoral geometry and joint surface areas in 73 species belonging to six mammalian orders (including primates) demonstrate that positive allometry of joint surface areas is not a general phenomenon for mammals and cannot have its basis among Anthropoidea in the biomechanics of weight bearing. We argue that, to the extent that positive allometric scaling of joint surface areas occurs in anthropoid primates, it is an artifact of differences in positional behaviour among distinct taxonomic groups that also happen to differ widely in body weight. Furthermore, we argue that, among mammals ranging in body size from sportive lemurs to giant pandas, functionally similar groups tend to exhibit: (1) linear dimensions (especially diameters and shaft circumferences) that scale in direct proportion to each other; and (2) joint surface areas that scale in direct proportion to the squares of linear dimensions and to the 2/3 power of body mass. In other words, limb bones of functionally similar animals fit the theoretical model of geometric similarity (or skeletal isometry). Differences in relative sizes of joint surface areas are related to differences in force transmission and movement potential among functionally distinct groups of animals.  相似文献   
6.
Bordetella pertussis adenylate cyclase (AC) toxin is a calmodulin-activated adenylate cyclase enzyme which has the capacity to enter eukaryotic target cells and catalyze the conversion of endogenous ATP into cyclic AMP. In this work, the AC holotoxin molecule is identified and isolated. It is a single polypeptide of apparent 216 kDa as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Monoclonal antibodies which immunoprecipitate AC activity from extracts of wild type B. pertussis (BP338) react with this 216-kDa band on Western blots, and it is absent from a transposon Tn5 mutant (BP348) specifically lacking AC toxin. Isolation of the 216-kDa protein to greater than 85% purity by hydrophobic chromatography, preparative sucrose gradient centrifugation, and affinity chromatography using either calmodulin-Sepharose or monoclonal antibody coupled to Sepharose 4B yields stepwise increases in AC toxin potency, to a maximum of 88.3 mumol of cAMP/mg of target cell protein/mg of toxin. Electroelution of the 216-kDa band following sodium dodecyl sulfate-polyacrylamide gel electrophoresis yields a preparation with both AC enzyme and toxin activities. These data indicate that this protein represents the AC holotoxin molecule.  相似文献   
7.
Sulfate reduction and S-oxidation in a moorland pool sediment   总被引:3,自引:2,他引:1  
In an oligotrophic moorland pool in The Netherlands, S cycling near the sediment/water boundary was investigated by measuring (1) SO4 2– reduction rates in the sediment, (2) depletion of SO4 2– in the overlying water column and (3) release of35S from the sediment into the water column. Two locations differing in sediment type (highly organic and sandy) were compared, with respect to reduction rates and depletion of SO4 2– in the overlying water.Sulfate reduction rates in sediments of an oligotrophic moorland pool were estimated by diagenetic modelling and whole core35SO4 2– injection. Rates of SO4 2– consumption in the overlying water were estimated by changes in SO4 2– concentration over time in in situ enclosures. Reduction rates ranged from 0.27–11.2 mmol m–2 d–1. Rates of SO4 2– uptake from the enclosed water column varied from –0.5, –0.3 mmol m–2 d–1 (November) to 0.43–1.81 mmol m–2 d–1 (July, August and April). Maximum rates of oxidation to SO4 2– in July 1990 estimated by combination of SO4 2– reduction rates and rates of in situ SO4 2– uptake in the enclosed water column were 10.3 and 10.5 mmol m–2 d–1 at an organic rich and at a sandy site respectively.Experiments with35S2– and35SO4 2– tracer suggested (1) a rapid formation of organically bound S from dissimilatory reduced SO4 2– and (2) the presence of mainly non SO4 2–-S derived from reduced S transported from the sediment into the overlying water. A35S2– tracer experiment showed that about 7% of35S2– injected at 1 cm depth in a sediment core was recovered in the overlying water column.Sulfate reduction rates in sediments with higher volumetric mass fraction of organic matter did not significantly differ from those in sediments with a lower mass fraction of organic matter.Corresponding author  相似文献   
8.
1. The effect of light intensity on photosynthesis and the fate of newly fixed organic carbon was compared for three characean algae collected at the same depth (10 m) but differing in their depth distributions. For each species we determined photosynthesis–irradiance (P–E) responses, the partitioning of newly fixed carbon into four intracellular pools (low molecular‐weight compounds, polysaccharides, lipids and proteins) and the extracellular organic carbon (EOC) release at a range of photon flux densities (PFD) 0–60 μmol m–2 s–1. 2. The P–E responses differed between the three species, with the light compensation point (Ec) and dark respiration rate highest in the shallowest species (Chara fibrosa), intermediate in the mid‐range species (C. globularis) and lowest in the deepest species (C. corallina). Photosynthetic efficiency (α) and photosynthesis: respiration ratios were lowest in C. fibrosa and highest in C. corallina. 3. In all three species, the low molecular weight pool was the principal photosynthetic product (>60% of fixed C) at 3 μmol m–2 s–1 PFD, but its proportional contribution decreased rapidly with increasing irradiance. Polysaccharide rose to become the major product (>35% of fixed C) at saturating PFD (35 μmol m–2 s–1). 4. Protein synthesis was saturated at 5 μmol m–2 s–1 in all species and was consistently a lower proportion of the fixed carbon in C. corallina than the other species. The fraction incorporated in the lipid pool increased slightly with irradiance but was always less than 10% of fixed C, while the proportion lost as EOC was unaffected by light, being significantly higher in C. fibrosa than the other species. 5. A kinetic experiment with C. fibrosa at 35 μmol m–2 s–1 PFD revealed a continued increase in net polysaccharide, protein and lipid synthesis during a 22.5‐h light period, whereas the net size of the low molecular weight pool remained constant. In a subsequent dark period, protein and lipid synthesis continued at the expense of the polysaccharide and low‐molecular‐weight pools. The EOC release rose to a constant low release in the light, then peaked slightly immediately after the dark–light transition before returning to the same rate as in the light. Extrapolating these data over 24 h suggests that the proportion of fixed carbon lost as EOC may be as high as 10% in this species. 6. The interspecific differences in carbon acquisition between the three species reflected their depth distributions, with the deeper species having more efficient photosynthetic metabolism, lower P:R ratios and less EOC release, although no apparent differences in internal partitioning of photosynthate.  相似文献   
9.
This paper documents an exercise to synthesize and assess the best available scientific knowledge on the effectiveness of different farm practices at enhancing natural pest regulation in agriculture. It demonstrates a novel combination of three approaches to evidence synthesis—systematic literature search, collated synopsis and evidence assessment using an expert panel. These approaches follow a logical sequence moving from a large volume of disparate evidence to a simple, easily understandable answer for use in policy or practice. The example of natural pest regulation in agriculture was selected as a case study within two independent science-policy interface projects, one European and one British. A third funder, a private business, supported the final stage to translate the synthesized findings into a useful, simplified output for agronomists. As a whole, the case study showcases how a network of scientific knowledge holders and knowledge users can work together to improve the use of science in policy and practice. The process identified five practices with good evidence of a benefit to natural pest regulation, with the most beneficial being ‘Combine trap and repellent crops in a push–pull system’. It highlights knowledge gaps, or potential research priorities, by showing practices considered important by stakeholders for which there is not enough evidence to make an assessment of effects on natural pest regulation, including ‘Alter the timing of pesticide application.’ Finally, the process identifies several important practices where the volume of evidence of effects on natural pest regulation was too large (>300 experimental studies) to be summarised with the resources available, and for which focused systematic reviews may be the best approach. These very well studied practices include ‘Reduce tillage’ and ‘Plant more than one crop per field’.  相似文献   
10.
Gelsolin is a cytoskeletal protein which participates in actin filament dynamics and promotes cell motility and plasticity. Although initially regarded as a tumor suppressor, gelsolin expression in certain tumors correlates with poor prognosis and therapy-resistance. In vitro, gelsolin has anti-apoptotic and pro-migratory functions and is critical for invasion of some types of tumor cells. We found that gelsolin was highly expressed at tumor borders infiltrating into adjacent liver tissues, as examined by immunohistochemistry. Although gelsolin contributes to lamellipodia formation in migrating cells, the mechanisms by which it induces tumor invasion are unclear. Gelsolin's influence on the invasive activity of colorectal cancer cells was investigated using overexpression and small interfering RNA knockdown. We show that gelsolin is required for invasion of colorectal cancer cells through matrigel. Microarray analysis and quantitative PCR indicate that gelsolin overexpression induces the upregulation of invasion-promoting genes in colorectal cancer cells, including the matrix-degrading urokinase-type plasminogen activator (uPA). Conversely, gelsolin knockdown reduces uPA levels, as well as uPA secretion. The enhanced invasiveness of gelsolin-overexpressing cells was attenuated by treatment with function-blocking antibodies to either uPA or its receptor uPAR, indicating that uPA/uPAR activity is crucial for gelsolin-dependent invasion. In summary, our data reveals novel functions of gelsolin in colorectal tumor cell invasion through its modulation of the uPA/uPAR cascade, with potentially important roles in colorectal tumor dissemination to metastatic sites.  相似文献   
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