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41.
BUTLER DECLAN M.; ?STGAARD KJETILL; BOYEN CATHERINE; EVANS LEONARD V.; JENSEN ARNE; KLOAREG BERNARD 《Journal of experimental botany》1989,40(11):1237-1246
In an investigation of the main factors determining protoplastyield in Laminaria saccharina and L. digitata, protoplasts wereisolated from epidermal, cortical and medullary cells of vegetativethallus by incubation with commercial cellulases, crude andpurified mannuronate lyases and purified guluronate lyases.Treatment of the tissue with the calcium chelator EGTA beforeenzymatic digestion greatly increased the protoplast yield.Preplasmolysis was also necessary to obtain large numbers ofhealthy protoplasts and this was most effective when carriedout during chelation with EGTA. Purification of the mannuronatelyases by ion exchange chromatography reduced the toxicity ofthe crude enzyme preparation. The activities of the wall degradingenzymes were differentially influenced by pH and the optimumfor alginate-lyase activity (8.0) was higher than that for cellulaseactivity (<6.0). Protoplast yield decreased linearly withincreasing pH in the enzyme medium over the range tested (6.08.0),and this suggests that cellulases are more critical to walldigestion than alginate-lyases. Ionic osmotica gave improvedyields compared with sugar alcohols or sugars. Increasing thecalcium concentration of the enzyme medium brought about anexponential decrease in protoplast yield and wall digestionwas almost completely inhibited at concentrations exceeding8.0 mol m3. However, low levels of calcium (<2.0 molm3) were beneficial to protoplast viability. Yields of107 to 108 protoplasts g1 fr. wt. were consistently obtainedand 20% to 30% of these regenerated new cell walls within 12d of culture. Key words: Laminaria protoplasts, cell wall, alginate-lyases 相似文献
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LEONARD A. ROSENBLUM 《American anthropologist》1973,75(6):2027-2027
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LEONARD F. RUGGIERO 《The Journal of wildlife management》2010,74(6):1179-1182
Abstract: Absence of scientific independence can be associated with a lack of impartiality and therefore with a lack of credibility. Yet scientific credibility is essential for effective participation in sociopolitical processes—processes that necessarily involve politics and often result in decisions about land management, conservation, and public policy. All scientists are aware of these processes, many wish to participate, and some wish to advocate for their personal policy preferences. However, scientists who lack impartiality often create the perception of bias, and they can suffer a concomitant loss of credibility. Some policy-makers also have personal preferences for certain policies, and the term normative policies can be used here even though all policies can be viewed as normative in the sense that they involve multiple inputs. Hence, the idea that scientists must provide unbiased information for unbiased application by policy-makers is sometimes wrong. For scientists to be effective participants in sociopolitical processes that lead to conservation policies or related actions, they should inform the public about issues while avoiding direct involvement in policy development and the political considerations this necessarily entails. Scientists should only participate in the decision-making process with impartial information and in their proper role as objective scientists. 相似文献
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1. The extent of spatial and temporal variation of microbial respiration was determined in a first-order, sand-bottomed, blackwater stream on the coastal plain of south-eastern Virginia, U.S.A.
2. Annual mean respiration rates (as g O2 m–3 h–1 ) differed significantly among substrata: leaf litter, 12.9; woody debris, 2.4; surface sediment, 0.8; hyporheic sediment, 0.4; water column, 0.003. Rates associated with wood were higher than those with leaves when expressed per unit surface area.
3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.
4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.
5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O2 m–2 yr–1 . Seventy per cent of respiration in the stream occurred in the hyporheic zone, 8–13% occurred in the surface sediment, leaf litter or woody debris, and < 1% occurred in the water column. Approximately 16% of total detritus, or 40% of non-woody detritus, stored in the stream during the year was lost to microbial respiration. 相似文献
2. Annual mean respiration rates (as g O
3. Highest respiration rates on leaves, wood and in the water column occurred during the summer, whereas rates in the sediments were greatest during the late autumn and winter. Water temperature, as well as particulate organic matter and nitrogen content of the substrata, was correlated positively with respiration rates.
4. A stepwise multiple regression showed that temperature and nitrogen content together explained 88% of the variation in respiration rates of leaves and wood. In contrast, particulate organic matter content and nitrogen content explained 89–90% of the variation in respiration in the sediments. Although water temperature was a significant factor in the sediment multiple regressions, its addition as an independent variable improved the regression models only slightly.
5. Annual mean respiration in the stream channel, based on the proportional amount of respiration occurring associated with each type of substratum during each month, was 1.1 kg O
49.
TIM J. CLOUGH JANET E. BERTRAM ROBERT R. SHERLOCK ROBERT L. LEONARD BARBARA L. NOWICKI† 《Global Change Biology》2006,12(3):477-488
There is considerable uncertainty in the estimates of indirect N2O emissions as defined by the intergovernmental panel on climate change's (IPCC) methodology. Direct measurements of N2O yields and fluxes in aquatic river environments are sparse and more data are required to determine the role that rivers play in the global N2O budget. The objectives of this research were to measure the N2O fluxes from a spring‐fed river, relate these fluxes to the dissolved N2O concentrations and NO3‐N loading of the river, and to try and define the indirect emission factor (EF5‐r) for the river. Gas bubble ebullition was observed at the river source with bubbles containing 7.9 μL N2O L?1. River NO3‐N and dissolved N2O concentrations ranged from 2.5 to 5.3 mg L?1 and 0.4 to 1.9 μg N2O‐N L?1, respectively, with N2O saturation reaching 404%. Floating headspace chambers were used to sample N2O fluxes. N2O‐N fluxes were significantly related to dissolved N2O‐N concentrations (r2=30.6) but not to NO3‐N concentrations. The N2O‐N fluxes ranged from 38–501 μg m?2 h?1, averaging 171 μg m?2 h?1 (±SD 85) overall. The measured N2O‐N fluxes equated to an EF5‐r of only 6.6% of that calculated using the IPCC methodology, and this itself was considered to be an overestimate because of the degassing of antecedent dissolved N2O present in the groundwater that fed the river. 相似文献
50.
LEONARD LIEBERMAN 《American anthropologist》2005,107(1):164-165