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1.
Foliage of Scots pine (Pinus sylvestris L.) and pedunculate oak (Quercus robur L.) was collected in a mixed pine/oak forest at canopy positions differing in radiation environment. In both species, chlorophyll (Chl) a/b ratios were higher in foliage of canopy positions exposed to higher irradiance as compared to more shaded crown layers. Throughout the growing season, pine needles exhibited significantly lower Chl a/b ratios than oak leaves acclimated to a similar photon availability. Hence, pine needles showed shade-type pigment characteristics relative to foliage of oak. At a given radiation environment, pine needles tended to contain more neoxanthin and lutein per unit of Chl than oak leaves. The differences in pigment composition between foliage of pine and oak can be explained by a higher ratio of outer antennae Chl to core complex Chl in needles of P. sylvestris which enhances the efficiency of photon capture under limiting irradiance. The shade-type pigment composition of pine relative to oak foliage could have been due to a reduced mesophyll internal photon exposure of chloroplasts in needles of Scots pine, resulting from their xeromorphic anatomy. Hence, the higher drought tolerance of pine needles could be achieved at the expense of shade tolerance. 相似文献
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This paper provides evidence for the identification of the language of the uncontacted indigenous group called Carabayo, who live in voluntary isolation in the Colombian Amazon region. The only linguistic data available from this group is a set of about 50 words, most of them without reliable translations, that were collected in 1969 during a brief encounter with one Carabayo family. We compare this material with various languages (once) spoken in the region, showing that four attested Carabayo forms (a first person singular prefix and words for ‘warm’, ‘father’, and ‘boy’) display striking similarities with Yurí and at least 13 Carabayo forms display clear correspondences with contemporary Tikuna. Tikuna and Yurí are the only two known members of the Tikuna-Yurí linguistic family. Yurí was documented in the 19th century but has been thought to have become extinct since. We conclude that the Carabayo – directly or indirectly – descend from the Yurí people whose language and customs were described by explorers in the 19th century, before they took up voluntary isolation, escaping atrocities during the rubber boom in the early 20th century. 相似文献
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《Biochimica et Biophysica Acta (BBA)/Lipids and Lipid Metabolism》1981,663(2):390-400
The in vitro binding of α-tocopherol to microsomes of lung, liver, heart and brain of the rat was studied with the insoluble tocopherol ligand presented as a complex with bovine serum albumin. Under these conditions, all microsomes showed nonsaturable binding of α-tocopherol and the amount bound to microsomes was linearly proportional to the concentration of albumin-complexed tocopherol. Increasing the amount of α-tocopherol bound to microsomes in this manner reduced the extent of lipid peroxidation induced by added ferrous iron. The apparent affinities of the microsomes for α-tocopherol, as indicated by the amount bound at a given concentration of albumin-complexed tocopherol, decreased in the order brain > liver ≈ heart > lung. The differences in affinity did not correlate with total fatty acid content (r = − 0.39), total unsaturated fatty acid content (r = − 0.26), or with the content of fatty acids containing two or more double bonds (r = − 0.01). A high positive correlation was found with the content of fatty acids containing three or more double bonds (r = + 0.96). Since lung microsomes contain approx. 6-times the tocopherol levels of liver and brain and about twice that of heart microsomes, these results show that the in vivo levels of microsomal tocopherol do not reflect microsomal affinity for this biological antioxidant. 相似文献
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《BBA》2006,1757(9-10):1073-1083
Mitochondrial Complex II (succinate:ubiquinone oxidoreductase) is purified in a partially inactivated state, which can be activated by removal of tightly bound oxaloacetate (E.B. Kearney, et al., Biochem. Biophys. Res. Commun. 49 1115–1121). We crystallized Complex II in the presence of oxaloacetate or with the endogenous inhibitor bound. The structure showed a ligand essentially identical to the “malate-like intermediate” found in Shewanella Flavocytochrome c crystallized with fumarate (P. Taylor, et al., Nat. Struct. Biol. 6 1108–1112) Crystallization of Complex II in the presence of excess fumarate also gave the malate-like intermediate or a mixture of that and fumarate at the active site. In order to more conveniently monitor the occupation state of the dicarboxylate site, we are developing a library of UV/Vis spectral effects induced by binding different ligands to the site. Treatment with fumarate results in rapid development of the fumarate difference spectrum and then a very slow conversion into a species spectrally similar to the OAA-liganded complex. Complex II is known to be capable of oxidizing malate to the enol form of oxaloacetate (Y.O. Belikova, et al., Biochim. Biophys. Acta 936 1–9). The observations above suggest it may also be capable of interconverting fumarate and malate. It may be useful for understanding the mechanism and regulation of the enzyme to identify the malate-like intermediate and its pathway of formation from oxaloacetate or fumarate. 相似文献
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《Bioscience, biotechnology, and biochemistry》2013,77(6):1077-1079
Cells at the apical part of developing stolons of the potato (Solatium tuberosum L. cv. Norin 1) were analyzed for the occurrence of putative precursors to amyloplasts, designated “amyloplast initial.” Ultrastructural studies showed that the cells contained the expected novel organelle. It was about 1 μm in diameter, devoid of thylakoid membranes, and was stained to a similar extent as the stroma of amyloplasts by uranyl acetate and lead citrate. Formation of thylakoid membranes and starch granules takes place at an early stage of development of these initials when they are just a few μm in diameter. At this stage, proliferation of the initials takes places by division at random sites. 相似文献
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Does the response of the intestinal epithelium to keratinocyte growth factor vary according to the method of administration? 总被引:3,自引:0,他引:3
BACKGROUND: Keratinocyte growth factor (KGF) is a potent mitogen and may be of value for the treatment of conditions such as short bowel syndrome and chemotherapy-induced mucositis. However the most efficacious route and method of administration is unclear. METHODS: Rats maintained by total parenteral nutrition (TPN) were given KGF (1 mg/kg/rat/day, i.v.) infused continuously or as a once-daily injection. The same dose was also given s.c. to chow-fed rats. Changes in gut growth were assessed by measurement of wet weight, proliferation (vincristine induced metaphase arrest) and crypt branching index. Changes in gut hormone profile were also determined to examine if any trophic effects were mediated via this mechanism. RESULTS: KGF caused a 70-100% increase in wet weight of the stomach, small and large intestine of TPN-fed rats (P < 0.01) with no significant differences seen between the two methods of administration. The increase in metaphase counts was greatest in the stomach (about seven-fold P < 0.01), but was less pronounced in the distal small intestine and colon (about 50% increase). The trophic effect of KGF was much less prominent in orally-fed rats. Crypt branching index was significantly reduced by KGF in the proximal small intestine of TPN, but not orally-fed rats. Plasma gastrin, PYY, total glucagon, enteroglucagon and GLP-1 all increased by two-three-fold (all P < 0.01) in response to KGF whereas insulin levels fell by about 25% in the TPN group. CONCLUSIONS: The mitogenic action of KGF occurred predominantly in the stomach and proximal small intestine. Its efficacy was less pronounced in orally-fed animals, suggesting KGF may be of greatest benefit in conditions associated with lowered intestinal proliferation. Clinical trials of KGF can probably use single daily i.v. injections without reduction in efficacy. 相似文献
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Nonhomologous DNA end joining (NHEJ) is the primary pathway for repair of double-strand DNA breaks in human cells and in multicellular eukaryotes. The causes of double-strand breaks often fragment the DNA at the site of damage, resulting in the loss of information there. NHEJ does not restore the lost information and may resect additional nucleotides during the repair process. The ability to repair a wide range of overhang and damage configurations reflects the flexibility of the nuclease, polymerases, and ligase of NHEJ. The flexibility of the individual components also explains the large number of ways in which NHEJ can repair any given pair of DNA ends. The loss of information locally at sites of NHEJ repair may contribute to cancer and aging, but the action by NHEJ ensures that entire segments of chromosomes are not lost. 相似文献
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Amelia Y. Nguyen William P. Bricker Hao Zhang Daniel A. Weisz Michael L. Gross Himadri B. Pakrasi 《Photosynthesis research》2017,132(1):95-106
Phycobilisome (PBS) complexes are massive light-harvesting apparati in cyanobacteria that capture and funnel light energy to the photosystem. PBS complexes are dynamically degraded during nutrient deprivation, which causes severe chlorosis, and resynthesized during nutrient repletion. PBS degradation occurs rapidly after nutrient step down, and is specifically triggered by non-bleaching protein A (NblA), a small proteolysis adaptor that facilitates interactions between a Clp chaperone and phycobiliproteins. Little is known about the mode of action of NblA during PBS degradation. In this study, we used chemical cross-linking coupled with LC-MS/MS to investigate the interactions between NblA and phycobiliproteins. An isotopically coded BS3 cross-linker captured a protein interaction between NblA and β-phycocyanin (PC). LC-MS/MS analysis identified the amino acid residues participating in the binding reaction, and demonstrated that K52 in NblA is cross-linked to T2 in β-PC. These results were modeled onto the existing crystal structures of NblA and PC by protein docking simulations. Our data indicate that the C-terminus of NblA fits in an open groove of β-PC, a region located inside the central hollow cavity of a PC rod. NblA may mediate PBS degradation by disrupting the structural integrity of the PC rod from within the rod. In addition, M1-K44 and M1-K52 cross-links between the N-terminus of NblA and the C-terminus of NblA are consistent with the NblA crystal structure, confirming that the purified NblA is structurally and biologically relevant. These findings provide direct evidence that NblA physically interacts with β-PC. 相似文献
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Ischemic preconditioning affords the most powerful protection to a heart submitted to a prolonged ischemia-reperfusion. During the past decade, a huge amount of work allowed to better understand the features of this protective effect as well as the molecular mechanisms. Ischemic preconditioning reduces infarct size and improves functional recovery; its effects on arrhythmias remain debated. Triggering of the protection involves cell surface receptors that activate pro-survival pathways including protein kinase C, PI3-kinase, possibly Akt and ERK1/2, whose downstream targets remain to be determined. Much attention has been recently focused on the role of mitochondrial K(+)ATP channels and the permeability transition pore that seem to play a major role in the progression toward irreversible cellular injury. Based on these experimental studies attempts have been made to transfer preconditioning from bench to bedside. Human experimental models of ischemic preconditioning have been set up, including cardiac surgery, coronary angioplasty or treadmill exercise, to perform pathophysiological studies. Yet, protecting the heart of CAD (coronary artery disease) patients requires a pharmacological approach. The IONA trial has been an example of the clinical utility of preconditioning. It helped to demonstrate that chronic administration of nicorandil, a K(+)ATP opener that mimics ischemic preconditioning in experimental preparations, improves the cardiovascular prognosis in CAD patients. Recent experimental studies appear further encouraging. It appears that "postconditioning" the heart (i.e. performing brief episodes of ischemia-reperfusion at the time of reperfusion) is as protective as preconditioning. In other words, a therapeutic intervention performed as late as at the time of reflow can still significantly limit infarct size. Further work is needed to determine whether this may be transferred to the clinical practice. 相似文献
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Are the semicircular canals of the European mole, Talpa europaea, adapted to a subterranean habitat?
A McVean 《Comparative biochemistry and physiology. Part A, Molecular & integrative physiology》1999,123(2):173-178
The mechanical sensitivity of vertebrate semicircular canals is directly influenced by the canal dimensions. Three key canal parameters, whose dimensions have been shown to be critical in determining the mechanical sensitivity of semicircular canals, are the streamline length, the cross-sectional area of the canal lumen and the plane area. These parameters were measured in ten specimens of adult T. europaea and compared with the dimensions of the same parameters in R. norvegicus. The major determinant of sensitivity, canal lumen area, is significantly larger in T. europaea. 相似文献
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The tobacco budworm, Heliothis virescens, was reared on diets containing various low concentrations of the spore-δ-endotoxin complex of Bacillus thuringiensis var. kurstaki. As the concentration of the complex was increased, the development time increased, pupal weights of the surviving larvae decreased, and the numbers of larvae able to complete the cycle and reach adulthood was reduced. In all these cases, the changes were directly proportional to the log of the concentration of the complex in the diet. Fertility and fecundity were reduced in adult tobacco budworms emerging from larvae reared in the presence of the toxin, but these effects seemed to result indirectly from the general debilitation produced by the toxin, since their occurrence was not related to the concentration of the toxin in the diet. 相似文献
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Brief exposure to the protein neurotoxin, β-bungarotoxin, is known to disrupt neuromuscular transmission irreversibly by blocking the release of transmitter from the nerve terminal. This neurotoxin also has a phospholipase A2 activity, although phospholipases in general are not very toxic. To determine if the toxicity of this molecule might result from specific binding to neural tissue, we have looked for high affinity, saturable binding using 125I-labeled toxin. At low membrane protein concentration 125I-labeled toxin binding was directly proportional to the amount of membrane; at fixed membrane concentration 125I-labeled toxin showed saturable binding. It was unlikely that iodination markedly changed the toxin's properties since the iodinated toxin had a comparable binding affinity to that of native toxin as judged by competition experiments. Comparison of toxin binding to brain, liver and red blood cell membranes showed that all had high affinity binding sites with dissociation constants between one and two nanomolar. This is comparable to the concentrations previously shown to inhibit mitochondrial function. However, the density of these sites showed marked variation such that the density of sites was 13.0 pmol/mg protein for a brain membrane preparation, 2.4 pmol/mg for liver and 0.25 pmol/mg for red blood cell membranes.In earlier work we had shown that calcium uptake by brain mitochondria is inhibited at much lower toxin concentrations than is liver mitochondrial uptake. Both liver and brain mitochondria bind toxin specifically, but the density of 125I-labeled toxin binding sites on brain mitochondrial prepartions () exceeded by a factor of ten the density on liver mitochondrial preparations (). It is also shown that the labeled toxin does not cross synaptosomal membranes, suggesting that mitochondria may not be the site of action of the toxin in vivo. We conclude the β-bungarotoxin is an enzyme which can bind specifically with high affinity to cell membranes. 相似文献
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Macoris Mde L Andrighetti MT Takaku L Glasser CM Garbeloto VC Bracco JE 《Memórias do Instituto Oswaldo Cruz》2003,98(5):703-708
Since the reintroduction of Aedes aegypti in the state of S o Paulo, in the middle of the 1980-decade, organophosphate insecticides are being used to control the dengue vector. In 1996, an annual program for monitoring the susceptibility of Ae. aegypti to the insecticides was implemented. Some of the results of this monitoring program are presented. Ae. aegypti populations from ten localities have been submitted to bioassays with the diagnostic dose of temephos and fenitrothion. Only two (Mar lia and Presidente Prudente) remain susceptible to both insecticides and one (Santos) exhibits true resistance. Ae. aegypti from the remaining localities showed an incipient altered susceptibility. Resistance ratios varied from 1.2 to 2.9 for temephos and from 1.5 to 3.2 to fenitrothion, indicating moderate levels of resistance. Biochemical assays did not detect alterations in the enzyme acetilcholinesterase, but indicated that resistance is associated with esterases. 相似文献