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Ethylene (C2H4) produced by soil microorganisms at concentrations sufficient to affect root development has previously been identified in the gas phase of anaerobic or partially anaerobic soils. This research was initiated to establish the existence of and to determine concentrations of C2H4 in soil in relation to matric potential, oxygen (O2) and compaction, and effects on growth and tuber yield of potatoes (Solanum tuberosum L.). Ethylene initially appeared at the 10-cm depth after 2.5-cm/day increments of water were applied by furrow irrigation for 3 days. Levels of C2H4 increased to 18.4 ppm and O2 decreased to 8% after 12.5 cm of water had been applied in 2.5-cm increments for 5 days. Ethylene was found in two partially compacted plots. High C2H4 concentrations and low O2 levels in the soil atmosphere were associated with reduced top growth, leaf injury, lower tuber quality, and a 20% decrease in potato yields. Since C2H4 and low O2 levels occur simultaneously in soil, further research is needed to identify their individual effects on root and tuber development.  相似文献   
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A series of 14 new analogs of α-conotoxin PnIA Conus pennaceus was synthesized and tested for binding to the human α7 nicotinic acetylcholine receptor (nAChR) and acetylcholine-binding proteins (AChBP) Lymnaea stagnalis and Aplysia californica. Based on computer modeling and the X-ray structure of the A. californica AChBP complex with the PnIA[A10L, D14K] analog, single and multiple amino acid substitutions were introduced in α-conotoxin PnIA aimed at compounds of higher affinity and selectivity. Three analogs, PnIA[L5H], PnIA[A10L, D14K] and PnIA[L5R, A10L, D14R], have high affinities for AChBPs or α7 nAChR, as found in competition with radioiodinated α-bungarotoxin. That is why we prepared radioiodinated derivatives of these α-conotoxins, demonstrated their specific binding and found that among the tested synthetic analogs, most had almost 10-fold higher affinity in competition with radioactive α-conotoxins as compared to competition with radioactive α-bungarotoxin. Thus, radioiodinated α-conotoxins are a more sensitive tool for checking the activity of novel α-conotoxins and other compounds quickly dissociating from the receptor complexes.  相似文献   
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Saccharophagus degradans 2-40 is a γ-subgroup proteobacterium capable of using many of the complex polysaccharides found in the marine environment for growth. To utilize these complex polysaccharides, this bacterium produces a plethora of carbohydrases dedicated to the processing of a carbohydrate class. Aiding in the identification of the contributing genes and enzymes is the known genome sequence for this bacterium. This review catalogs the genes and enzymes of the S. degradans genome that are likely to function in the systems for the utilization of agar, alginate, α- and β-glucans, chitin, mannans, pectins, and xylans and discusses the cell biology and genetics of each system as it functions to transfer carbon back to the bacterium.  相似文献   
75.
Two hypotheses that could explain increases in the biomass and production of lotic periphytic communities in acidified habitats were tested: 1) a greater bioavailability of P due to its greater release from sediments at low pH, and 2) utilization of S from the H2SO4 addition. The experiments were performed in semi-natural conditions by submitting the periphyton to either continuous or episodic acidification. The uptake of P and S by periphyton were determined at different times during the treatments. The increases in P and S uptake, in acidified habitats, are compatible with both hypotheses and could account for the increase in periphytic biomass and production.  相似文献   
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We previously reported that heat pretreatment of corn fiber (150 degrees C, 1 h) caused a tenfold increase in the levels of extractable gamma-tocopherol. The current study was a reinvestigation of the previous effect, using improved methods (HPLC with fluorescence detection, diode-array UV detection, and mass spectrometry) for tocol analysis. Heat pretreatment did not cause an increase in the levels of any of the tocopherols or tocotrienols in corn fiber oil, but lowered the levels of three of the tocols and had no effect on the levels of the other two tocols. Heat pretreatment of corn germ had a similar effect. UV and mass spectra indicated that the peak that we had identified as gamma-tocopherol in our previous report was probably a mixture of oxidation products of triacylglycerols. Thus, heat treatment of corn germ or other corn-oil containing fractions at high temperatures leads to decreases in gamma-tocopherol, gamma-tocotrienol, and delta-tocotrienol and to the production of triacylglycerol oxidation products.  相似文献   
78.
OBJECTIVE: To evaluate the topical effect of various agents, currently used in the treatment of melting ulcers, on gelatinase activity present in the tear film of normal dogs. ANIMAL STUDIED: Eight normal adult beagles. PROCEDURES: Each animal received the following agents: cyclosporine A 1%, N-acetylcysteine 10%, ciprofloxacin 0.3%, ethylenediaminetetraacetic acid (EDTA) 1%, doxycycline 0.001%, polysulfated glycosaminoglycans (PSGAG) 5%, autoserum, and artificial tears during a 48-h period following a Latin square design. Tear samples were collected with micro-capillary pipettes following a corneal surface irrigation of each eye with sterile saline on four different occasions. Basal and total gelatinase activities were evaluated by optical density after processing in a commercial gelatinase activity assay. From the optical density ratio, a semi-quantitative measure of gelatinase activity was obtained. Basal and total activities were measured in all samples. RESULTS: The lowest total gelatinase activity, representing a percent decline in the enzyme activity although not significant, was observed 1 h after the last treatment in seven out of the eight ophthalmic agents; EDTA (68%), ciprofloxacin (76%), cyclosporine A (68%), doxycycline (47%), artificial tears (26%), PSGAG (25%), and N-acetylcysteine (20%). However, only the reduction observed with EDTA 6 h after the last treatment was significantly lower compared to the reduction observed with the artificial tears. CONCLUSION: This study indicated that only EDTA was able to significantly reduce the gelatinase activity in a persistent manner in the tear film of normal canine eyes. Further studies will be required to evaluate the effect of EDTA under ulcerative conditions and to more accurately ascertain the potential in vivo effect of the other agents.  相似文献   
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