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11.
Karen Castillioni Kevin Wilcox Lifen Jiang Yiqi Luo Chang Gyo Jung Lara Souza 《Ecology and evolution》2020,10(13):6702-6713
- Shifts in dominance and species reordering can occur in response to global change. However, it is not clear how altered precipitation and disturbance regimes interact to affect species composition and dominance.
- We explored community‐level diversity and compositional similarity responses, both across and within years, to a manipulated precipitation gradient and annual clipping in a mixed‐grass prairie in Oklahoma, USA. We imposed seven precipitation treatments (five water exclusion levels [?20%, ?40%, ?60%, ?80%, and ?100%], water addition [+50%], and control [0% change in precipitation]) year‐round from 2016 to 2018 using fixed interception shelters. These treatments were crossed with annual clipping to mimic hay harvest.
- We found that community‐level responses were influenced by precipitation across time. For instance, plant evenness was enhanced by extreme drought treatments, while plant richness was marginally promoted under increased precipitation.
- Clipping promoted species gain resulting in greater richness within each experimental year. Across years, clipping effects further reduced the precipitation effects on community‐level responses (richness and evenness) at both extreme drought and added precipitation treatments.
- Synthesis: Our results highlight the importance of studying interactive drivers of change both within versus across time. For instance, clipping attenuated community‐level responses to a gradient in precipitation, suggesting that management could buffer community‐level responses to drought. However, precipitation effects were mild and likely to accentuate over time to produce further community change.
12.
Dennis W. Jung Gerald P. Brierley 《Biochemical and biophysical research communications》1982,106(4):1372-1377
Heart mitochondria respiring in the presence of Pi release endogenous K+ to a sucrose medium when an uncoupler is added. The uncoupled mitochondria retain K+, however, if the oxidation of NAD(P)H is prevented by the addition of rotenone or antimycin. Addition of rotenone, once the uncoupler-dependent K+-efflux has been initiated, results in a rapid reduction of NAD(P) and a simultaneous decrease in permeability to K+. These changes are independent of respiration. The results suggest that a latent pathway for K+-permeability is present in the membrane, that it can be opened and closed reversibly, and that it reflects, either directly or indirectly, the redox status of mitochondrial pyridine nucleotides. The possible relationship of this putative pathway to those available for Ca2+ uptake and release is considered. 相似文献
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14.
Energy expenditure was measured during pregnancy in seven primigravid women at 12-15, 25-28, and 34-36 weeks and after the cessation of lactation. On each occasion the resting metabolic rate and the increase in metabolic rate after ingestion of a liquid test meal were measured by indirect calorimetry. In absolute terms the resting metabolic rate increased steadily during pregnancy but when expressed per unit of body weight no change was found. The energetic response to a mixed constituent meal was significantly reduced by 28% in the middle trimester of pregnancy. These findings suggest a possible maternal adaptation to increase energetic efficiency at a time when the energy demands of the fetus are high. 相似文献
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16.
Jong-Jin Kim Ill-Min Chung Jae-Chul Jung Min-Young Kim 《Journal of enzyme inhibition and medicinal chemistry》2013,28(1):247-250
The whole plants of Carpesium genus are used in traditional medicine as anti-pyretic, analgesic and vermifugic, including a topical application for sores and inflammation. A previous study on Carpesium genus suggested that the antiplasmodial activity against Plasmodium falciparum was due to the existence of 11(13)- dehydroivaxillin (DDV) from EtOAc extracts of C. ceruum (Compositae). Here, the antimalarial activity of DDV was evaluated against Plasmodium berghei in mice. The LD50 of the compound was determined as 51.2 mg/kg, while doses of 124 mg/kg and above were found to be lethal to mice. DDV (2, 5, 10 mg/kg/day) exhibited a significant blood schizontocidal activity in 4-day early infection, repository evaluation and in an established infection with a significant mean survival time comparable to that of the standard drug, chloroquine, 5 mg/kg/day. DDV possesses a promising antiplasmodial activity, which can be exploited in malaria therapy. 相似文献
17.
The CO-stretching mode of the carbon monoxide ligand in reduced cytochrome P450cam, in the absence or presence of camphor and in the presence of nine different camphor analogues, was measured at room temperature using Fourier transform infrared spectroscopy. Substrate-free cytochrome P450cam--CO reveals a broad, slightly structured band resulting from an overlap of several stretching mode signals. The multitude of the signals indicates that cytochrome P450 exists in a dynamic equilibrium of several conformational substates. Binding of camphor or camphor analogues strongly influences this equilibrium. For substrate analogues which are not able to form a hydrogen bond to the hydroxyl group of tyrosine 96, the CO-stretching band is rather broad and asymmetric. In contrast, substrate analogues with one quinone group which form a hydrogen bond to the Tyr96 OH induce a shift and a sharpening of the CO-stretching mode band. For substrate analogues with two hetero groups, the infrared spectrum is slightly asymmetric or a minor band appears. Sterical hindrance, substrate mobility, and protein flexibility finally determine the position and width of the CO-stretching mode signals. 相似文献
18.
The accumulation and retention of Ca(2+) by yeast mitochondria (Saccharomyces cerevisiae) mediated by ionophore ETH 129 occurs with a variable efficiency in different preparations. Ineffective Ca(2+) transport and a depressed membrane potential occur in parallel, are exacerbated in parallel by exogenous free fatty acids, and are corrected in parallel by the addition of bovine serum albumin. Bovine serum albumin is not required to develop a high membrane potential when either Ca(2+) or ETH 129 are absent, and when both are present membrane potential is restored by the addition of EGTA in a concentration-dependent manner. Respiration and swelling data indicate that the permeability transition pore does not open in yeast mitochondria that are treated with Ca(2+) and ETH 129, whereas fatty acid concentration studies and the inaction of carboxyatractyloside indicate that fatty acid-derived uncoupling does not underlie the other observations. It is concluded that yeast mitochondria contain a previously unrecognized Ca(2+):2H(+) antiporter that is highly active in the presence of free fatty acids and leads to a futile cycle of Ca(2+) accumulation and release when exogenous Ca(2+) and ETH 129 are available. It is also shown that isolated yeast mitochondria degrade their phospholipids at a relatively rapid rate. The activity responsible is also previously unrecognized. It is Ca(2+)-independent, little affected by the presence or absence of a respiratory substrate, and leads to the hydrolysis of ester linkages at both the sn-1 and sn-2 positions of the glycerophospholipids. The products of this activity, through their actions on the antiporter, explain the variable behavior of yeast mitochondria treated with Ca(2+) plus ETH 129. 相似文献
19.
Structural basis of human erythrocyte glucose transporter function in reconstituted system. Hydrogen exchange 总被引:3,自引:0,他引:3
Hydrogen exchange kinetic behavior of human erythrocyte glucose transporter protein in vesicles was studied in the absence and in the presence of D-glucose or a well known inhibitor, cytochalasin B. This is to detect a proposed channel of water penetrating into the protein through which the sugar molecule passes and to monitor any conformational changes induced by the substrate or inhibitor. Analyses of the kinetic data revealed several classes of hydrogens which exchange with readily distinguishable rates. Of 660 hydrogens detected per transporter, approximately 30% exchanged with rates generally characterized as those of free amide hydrogens indicating they are interfaced to solvent water. Since the transporter is known to be embedded deep in the hydrophobic area of the membrane with minimum exposure to the outside of the membrane lipid bilayer, a significant portion of these free amide hydrogens must be at the purported channel rather than outside of the membrane. D-Glucose and cytochalasin B affected the exchange kinetics of these presumably channel-associated free amide hydrogens rather differently. D-Glucose reduced the apparent rate constants, but not the total number. Cytochalasin B on the other hand reduced the total number to one-half without significantly changing the apparent rate constants. The remaining 70% of the labeled hydrogens exchanged with much slower rates which vary 10-10,000-fold, indicating that they are internally structured peptide amide and side chain hydrogens. Both D-glucose and cytochalasin B further reduced the rates of these hydrogens, indicating a global stabilization of the protein structure. 相似文献
20.
The Korean species of the genus Eudorylas Aczél have been studied. A total of 16 species are arranged herein. Among them, E. paraappendiculatus sp. nov. is new to science, and E. nomurai Morakote et Yano, 1990 is newly recorded in the Korean fauna. 相似文献