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SIMPSON RR 《Texas reports on biology and medicine》1952,10(3):660-673
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ABSTRACT. The detailed behavioural mechanisms underlying an instance of compensation for changes in dietary nutrients are described for the first time in an insect. Nymphs of Locusta migratoria L. were given one of four artificial diets on the third day of the fifth instar, and their feeding patterns recorded in detail for 12 h. The diets represented combinations of two protein and two digestible carbohydrate levels (28% and 14% dry weight) presented in an otherwise complete nutrient mix. At the nutrient levels used, locusts regulated their intake of food with respect to protein but not digestible carbohydrate in the diet. They ate more of the lower protein diets by eating the same sized meals more frequently than insects fed on the higher protein diets. Compensation was not complete over the 12 h observation period: insects on the lower-protein diets ingested and absorbed 72% as much nitrogen as those insects fed on the higher-protein diets. Possible physiological mechanisms underlying the behavioural mechanisms are discussed. 相似文献
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Changes in nitrogenase activity (C2H2 reduction and H2 production),nodulated root respiration and the efficiency of nitrogenasefunctioning were measured in response to progressive dehydrationof nodules on intact well-watered plants of subterranean clover(Trifolium subterraneum L.) cv. Seaton Park. The nodulated rootsof vegetative plants grown to the 14-leaf stage were incubatedin a gas exchange system through which a continuous dry airstreamwas passed over an 8 d period. The root tips were immersed inan N-free nutrient solution during this time so that water andion uptake was unimpeded. The decline in nodulated root respirationresulting from nodule drying was associated with a continualreduction in respiration coupled to nitrogenase activity. Asnodule water potential (nod) decreased, the proportion of totalnodulated root respiration which was nitrogenase-linked declinedfrom 50% (day 1) to 33% (day 8). This was accompanied by a 79%reduction in specific nitrogenase activity (from 3.79 to 0.81umol C2H4 g1 nodule dry weight min1). Nodule dehydrationalso induced a decline in hydrogen (H2) production in air. Therelative decline in hydrogen production exceeded that of acetylenereduction activity and this resulted in an increase in the relativeefficiency of nitrogenase functioning. However, the carbon costof nitrogenase activity progressively increased above 2.0 molCO2 respired per mol C2H4 reduced as rood decreased below 0.4to 0.5 MPa. Consecutive measurements of the rates ofhydrogen evolution, 15N2 fixation and acetylene reduction activityon intact unstressed plants resulted in a C2H4/N2 conversionfactor of 4.08 and an electron balance of 1.08. These resultsindicated that the pre-decline rate of acetylene reduction activitymeasured in a flow-through system provided a valid measure ofthe total electron flux through nitrogenase. Key words: Subterranean clover, dehydration, efficiency, nitrogenase activity 相似文献
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High performance liquid chromatography with octadecylsilica (Bondapak C18/Poracil B) column packing was used to purify and separate cytokinins in Sorghum leaf extracts. The column size was 56 × 0.21 cm i.d. By gradient elution, using acidified water with increasing amounts of methanol, the major peaks of cytokinin activity, as determined by the callus tissue bioassay. were effectively separated from large amounts of extraneous impurities. These cytokinins were further separated on a microoctadecylsilica column (μBondapak C18, 30 × 0.4 cm i.d.) with a gradient of acidified water-acetonitrile. Zeatin and zeatin riboside gave distinct ultra violet absorption peaks which could be used for quantitative estimation. Biological activity corresponded to the elution of these peaks. These two cytokinins are the major cytokinins in Sorghum leaves. 相似文献
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XIAOJUAN FENG ANDRÉ J. SIMPSON WILLIAM H. SCHLESINGER MYRNA J. SIMPSON 《Global Change Biology》2010,16(7):2104-2116
The dynamics and fate of terrestrial organic matter (OM) under elevated atmospheric CO2 and nitrogen (N) fertilization are important aspects of long‐term carbon sequestration. Despite numerous studies, questions still remain as to whether the chemical composition of OM may alter with these environmental changes. In this study, we employed molecular‐level methods to investigate the composition and degradation of various OM components in the forest floor (O horizon) and mineral soil (0–15 cm) from the Duke forest free air CO2 enrichment (FACE) experiment. We measured microbial responses to elevated CO2 and N fertilization in the mineral soil using phospholipid fatty acid (PLFA) profiles. Increased fresh carbon inputs into the forest floor under elevated CO2 were observed at the molecular‐level by two degradation parameters of plant‐derived steroids and cutin‐derived compounds. The ratios of fungal to bacterial PLFAs and Gram‐negative to Gram‐positive bacterial PLFAs decreased in the mineral soil with N fertilization, indicating an altered soil microbial community composition. Moreover, the acid to aldehyde ratios of lignin‐derived phenols increased with N fertilization, suggesting enhanced lignin degradation in the mineral soil. 1H nuclear magnetic resonance (NMR) spectra of soil humic substances revealed an enrichment of leaf‐derived alkyl structures with both elevated CO2 and N fertilization. We suggest that microbial decomposition of SOM constituents such as lignin and hydrolysable lipids was promoted under both elevated CO2 and N fertilization, which led to the enrichment of plant‐derived recalcitrant structures (such as alkyl carbon) in the soil. 相似文献
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