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11.
Anders Michelsen 《Mycorrhiza》1993,4(1):11-15
Roots of 28 species of epiphytic vascular plants were collected on tree trunks and branches at six afromontane forest sites between 1700 and 3300 m above sea level in Bale Mountains National Park, Ethiopia. Seven of the 28 epiphyte species were colonized by vesicular-arbuscular mycorrhizal fungi (VAM). Mycorrhizal colonization only occurred at two of the six sites examined, at 2900 m and 3300 m, but more than one type of VAM endophyte was present in each case. Three facultative epiphytic species were all highly colonized by VAM on the forest floor, whereas roots from epiphytic habitats were weakly colonized. No correlations were found between VAM colonization, fine root diameter and root hair length, but VAM colonization and root hair abundance were negatively correlated. The lack of VAM colonization of potential, epiphytic host species at the majority of the sites examined points to the dispersal of VAM propagules as the factor limiting mycorrhizal colonization of epiphytic habitats. It is suggested that root systems of hemiepiphytic tree species serve as corridors between forest floor and tree trunks through which VAM may spread via hyphal growth. 相似文献
12.
Epoxide hydrolase (EC 3.3.2.3) activity was measured with [1-14C]cis-9,10-epoxystearic acid as the substrate. Homogenates were prepared from the endosperm tissue of germinating seeds of castor bean (Ricinus communis L. zanzibariensis). The activity of fatty-acid epoxide hydrolase was characterized with respect to dependence on time, amount of protein, pH and temperature. Analyses of enzyme distribution in endosperm, cotyledons, root and hypocotyl showed the highest total activity in the endosperm, less in the cotyledons and low activity in the root and hypocotyl. The specific activity was similar for cotyledons and endosperm. Analysis of the temporal expression of the enzyme in the endosperm during germination revealed high activity already in the imbibed seed. Activity was maximal between days four to six and then decreased at the end of one week. Subcellular fractionation of endosperm revealed a dual distribution of activity between the glyoxysomal and the cytosolic fractions. 相似文献
13.
Abstract: Prostaglandin E2 (PGE2) delivered to the spinal cord produces an increased sensitivity to noxious (hyperalgesia) and innocuous (allodynia) stimuli. The mechanisms that underlie this effect remain unknown, but a PGE2-evoked enhancement of spinal neurotransmitter release may be involved. To address this hypothesis, we examined the effect of PGE2 on CSF concentrations of amino acids and also the modulatory effect of PGE2 on capsaicin-evoked changes of spinal amino acid concentrations using a microdialysis probe placed in the lumbar subarachnoid space. Amino acids were quantified using HPLC with fluorescence detection. Addition of 1 mM, but not 10 or 100 µM, PGE2 to the perfusate for a 10-min period (flow rate, 5 µl/min) evoked an immediate increase (80–100%) in glutamate (Glu), aspartate (Asp), taurine (Tau), glycine (Gly), and γ-aminobutyric acid (GABA) concentrations. Similarly, capsaicin infusion (0.1–10 µM) induced a dose-dependent increase in Glu, Asp, Tau, Gly, GABA, and ethanolamine levels. Significant increases in amino acid levels evoked by PGE2 or capsaicin were associated with a touch-evoked allodynia. The combination of PGE2 (10 µM) and capsaicin (0.1 or 1.0 µM) at concentrations that individually had no effect together evoked a significant increase (60–100%) in Glu, Asp, Tau, Gly, and GABA concentrations and produced tactile allodynia. These data demonstrate that spinally delivered PGE2 or capsaicin substantially elevates CSF concentrations of both excitatory and inhibitory amino acids. The capacity of PGE2 to enhance and prolong capsaicin-evoked amino acid concentrations may be one of the mechanisms by which spinal PGE2 produces hyperalgesia and allodynia. 相似文献
14.
Annika Brunström Magnus Ingelman-Sundberg 《Biochemical and biophysical research communications》1980,95(1):431-439
The roles of rabbit liver cytochrome b5, epoxide hydrase and various forms of cytochrome P-450 in the NADPH-dependent metabolism of benzo(a)pyrene were examined. After incorporation of the purified enzymes into phospholipid vesicles, using the cholate gel filtration technique, the various types of cytochrome P-450 did exhibit different stereospecificities in the oxygenation of the substrate. Cytochrome P-450LM2 was found to efficiently convert benzo(a)pyrene in the presence of epoxide hydrase to 4,5-dihydroxy-4,5-dihydrobenzo(a)pyrene whereas cytochrome P-450LM4 primarily participated in the formation of 9,10-dihydroxy-9,10-dihydrobenzo(a)pyrene. By contrast, benzo(a)pyrene was not metabolized by cytochrome P-450LM3. Cytochrome b5 enhanced cytochrome P-450LM2-catalyzed oxygenations 5-fold, whereas cytochrome P-450LM4-dependent oxygenations proceeded at a 3 times higher rate when cytochrome b5 was present in the membrane. 相似文献
15.
A triacylglycerol analogue, rac-1,2-di-O-oleoyl-3-S-oleoyl-3-thioglycerol, was fed to rats and chyle acylglycerols were analyzed. Triacylglycerol was the dominating chyle lipid but X-triacyl-1-thioglycerol constituted approx. 6% of total chyle lipids. Its identity was verified by ultraviolet and mass spectra and its stereochemical structure by ORD and CD. The proportions of triacyl-1-thio-sn-glycerol/triacyl-3-thio-sn-glycerol were and in two experiments. Possible reasons for this stereospecificity are discussed. The study shows that the stereochemical configuration of lipids isolated from biological material can be assessed by ORD and CD. 相似文献
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Andrea Ghirardo Frida Lindstein Kerstin Koch Franz Buegger Michael Schloter Andreas Albert Anders Michelsen J. Barbro Winkler Jrg‐Peter Schnitzler Riikka Rinnan 《Global Change Biology》2020,26(3):1908-1925
Warming occurs in the Arctic twice as fast as the global average, which in turn leads to a large enhancement in terpenoid emissions from vegetation. Volatile terpenoids are the main class of biogenic volatile organic compounds (VOCs) that play crucial roles in atmospheric chemistry and climate. However, the biochemical mechanisms behind the temperature‐dependent increase in VOC emissions from subarctic ecosystems are largely unexplored. Using 13CO2‐labeling, we studied the origin of VOCs and the carbon (C) allocation under global warming in the soil–plant–atmosphere system of contrasting subarctic heath tundra vegetation communities characterized by dwarf shrubs of the genera Salix or Betula. The projected temperature rise of the subarctic summer by 5°C was realistically simulated in sophisticated climate chambers. VOC emissions strongly depended on the plant species composition of the heath tundra. Warming caused increased VOC emissions and significant changes in the pattern of volatiles toward more reactive hydrocarbons. The 13C was incorporated to varying degrees in different monoterpene and sesquiterpene isomers. We found that de novo monoterpene biosynthesis contributed to 40%–44% (Salix) and 60%–68% (Betula) of total monoterpene emissions under the current climate, and that warming increased the contribution to 50%–58% (Salix) and 87%–95% (Betula). Analyses of above‐ and belowground 12/13C showed shifts of C allocation in the plant–soil systems and negative effects of warming on C sequestration by lowering net ecosystem exchange of CO2 and increasing C loss as VOCs. This comprehensive analysis provides the scientific basis for mechanistically understanding the processes controlling terpenoid emissions, required for modeling VOC emissions from terrestrial ecosystems and predicting the future chemistry of the arctic atmosphere. By changing the chemical composition and loads of VOCs into the atmosphere, the current data indicate that global warming in the Arctic may have implications for regional and global climate and for the delicate tundra ecosystems. 相似文献
20.
Linda K. Petersson Daniel C. Dey Annika M. Felton Emile S. Gardiner Magnus Lf 《Ecology and evolution》2020,10(5):2626-2637
Failed oak regeneration is widely reported in temperate forests and has been linked in part to changed disturbance regimes and land‐use. We investigated if the North American fire–oak hypothesis could be applicable to temperate European oaks (Quercus robur, Quercus petraea) using a replicated field experiment with contrasting canopy openness, protection against ungulate browsing (fencing/no fencing), and low‐intensity surface fire (burn/no burn). Survival, relative height growth (RGRH), browsing damage on naturally regenerated oaks (≤300 cm tall), and changes in competing woody vegetation were monitored over three years. Greater light availability in canopy gaps increased oak RGRH (p = .034) and tended to increase survival (p = .092). There was also a trend that protection from browsing positively affected RGRH (p = .058) and survival (p = .059). Burning reduced survival (p < .001), nonetheless, survival rates were relatively high across treatment combinations at the end of the experiment (54%–92%). Most oaks receiving fire were top‐killed and survived by producing new sprouts; therefore, RGRH in burned plots became strongly negative the first year. Thereafter, RGRH was greater in burned plots (p = .002). Burning altered the patterns of ungulate browsing frequency on oaks. Overall, browsing frequency was greater during winter; however, in recently burned plots summer browsing was prominent. Burning did not change relative density of oaks, but it had a clear effect on competing woody vegetation as it reduced the number of individuals (p < .001) and their heights (p < .001). Our results suggest that young, temperate European oaks may respond similarly to fire as their North American congeners. However, disturbance from a single low‐intensity fire may not be sufficient to ensure a persistent competitive advantage—multiple fires and canopy thinning to increase light availability may be needed. Further research investigating long‐term fire effects on oaks of various ages, species‐specific response of competitors and implications for biodiversity conservation is needed. 相似文献