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1.
The influence of range of concentrations of potassium nitrate(Cm)in the medium surrounding the roots of decapitated Ricinuscommunis plants on: (a) the potassium concentration of the exudate(Cs), (b)the rate of exudation (fH2O), and (c) the flux of potassiuminto the exudate (fk) was investigated. A change in Cm couldinfluence exudation by altering the osmotic potential of themedium as will as by a change in potassium concentration, andthese two effect were separated in the following way. the effectof varying the potassium concentration was investigated usingmedia made isotonic with mannitol, whilst the osmotic effectwas investigated using mannitol solutions of various concentrationsbut of equal potassium concentration. An analysis of the resultsrevealed the existence of two salt-transfer processes, one independentof the water flux but dependent on the concentration of potassiumin the medium, the other linearly related to the flux of waterthrough the root system. The implications of these findingsin relation to the intact transpiring plant are discussed. 相似文献
2.
In Ditylenchus dipsaci the morphologically different anterior and posterior regions of the terminal excretory duct are separated by a constriction. Immediately posterior to the constriction is a valve-like structure composed of dense pieces integral with the wall of the duct. The posterior region is sometimes dilated at intervals along its length. The same structures are present in D. myceliophagus and D. destructor, but the dense pieces appear less well developed. A possible mode of action for the excretory system is discussed. 相似文献
3.
Many, but not all, visceral muscles in insects are innervatedby neurosecretory axons. The neurosecretory junctions with theheart muscle of the American cockroach, Periplaneta americana,show ultrastructural and electrophysiological evidence of chemicallytransmitting synapses, and cytochemical evidence for the presenceof monoamines. Electron microscopy of nerve terminals showsthat synaptic vesicles may be formed directly from electron-dense"neurosecretory" granules Neurotomy of motor axons to skeletal muscles in insects leadsto aggregation and clumping of synaptic vesicles after 48 hours.Treatment of in vitro nerve-muscle preparations with variousrespiratory poisons caused aggregation similar to that developedin neurotomized animals. This suggested that vesicle aggregationin both cases may have resulted from a decrease in availableadenosine triphosphate in the nerve terminal with subsequentalteration in the normal charge density which supports a repulsiveforce between the vesicles. 相似文献
4.
KENT KARLA S.; CONSOULAS CHRISTOS; DUNCAN KAREN; JOHNSTON REBECCA M.; LUEDEMAN RENE; LEVINE RICHARD B. 《Integrative and comparative biology》1995,35(6):578-584
During metamorphosis in the hawkmoth, Manduca sexta, the larvalthoracic legs are replaced by a new set of adult legs that includenew sensory neurons and muscles, and participate in new patternsof locomotor activity. Larval leg motoneurons persist to innervatethe new adult leg muscles, but undergo striking changes in dendriticmorphology that are regulated by the insect steroid, 20-hydroxyecdysone.In the periphery, the motor terminals regress as larval musclesdegenerate, and expand as new adult muscles form from myoblasts.Evidence obtained both in vivo and in vitro suggests that theproliferation of myoblasts during metamorphosis is dependentupon innervation. 相似文献
5.
G. E. Gregory 《Acta zoologica》1970,51(3):169-178
Improved fixation of ganglia of the central nervous system of Periplaneta americana and Schistocerca gregaria for silver staining by Power's (1943) modification of the Bodian protargol method is given by alcoholic Bouin aged for at least 40 days at 60° C. During impregnation of sections, increased copper and decreased pH give paler staining, more selective for nerve fibres. Prolonging impregnation from 24 to 48 hours weakens the stain and decreases selectivity. The intensity of the stain depends chiefly upon the amount of unreduced (developable) silver combined with the tissues; selectivity is determined mainly by the number and distribution of the reduced silver particles (‘nuclei’). In development, increased sodium sulphite gives more differentiation, increased hydroquinone gives less. Optimum developer composition depends upon impregnation, and thick sections need more differentiation than thinner ones. Within limits, change in one of the factors that control staining can be balanced by changes in others, but by suitable adjustment of the conditions the result can be varied from almost total staining of nerve fibres, for general neuroanatomy, to highly selective staining for tracing individual fibres. 相似文献
6.
The interactions of potassium ions and ATP on transport ATPase activity are discussed, and the interpretation of these interactions is shown to be often ambiguous. Caldwell''s (1968) Physiological Review model is discussed with particular reference to the observed kinetics of sodium: sodium exchange in red cells. Recent experimental work on the properties of the ouabain-sensitive component of potassium efflux from red cells is described. This component of efflux occurs only if either sodium or potassium are present in the external medium, but the effects of external sodium and potassium are not additive. The relation between ouabain-sensitive potassium efflux and the external concentration of sodium (in a potassium-free medium) or of potassium (in low- and high-sodium media) are described. When starved sodium-poor red cells are poisoned with iodoacetamide, loaded with phosphate, and incubated in high-sodium potassium-free media, the ouabain-sensitive efflux of potassium appears to be accompanied by the reversal of the entire ATPase system. About two to three potassium ions leave by the ouabain-sensitive route for each molecule of ATP synthesized. If potassium is present in the external medium, no ouabain-sensitive synthesis of ATP occurs and the ouabain-sensitive efflux of potassium presumably involves the reversal of only the last part of the ATPase system. 相似文献
7.
Eric Bonabeau 《Ecosystems》1998,1(5):437-443
Social insect societies are complex adaptive systems that self-organize within a set of constraints. Although it is important to acknowledge that global order in social insects can arise as a result of internal interactions among insects, it is equally important to include external factors and constraints in the picture, especially as the colony and its environment may influence each other through interactions among internal and external factors. The scope of this remark goes beyond social insects and applies to a wide range of biological systems, including ecosystems. Received 14 April 1998; accepted 7 July 1998. 相似文献
8.
Norbert H. Haunerland 《Comparative biochemistry and physiology. Part B, Biochemistry & molecular biology》1997,117(4):475-482
In migrating lepidopteran and orthopteran insects, lipid is the preferred fuel for sustained flight activity. Diacylglycerol is delivered by lipophorin to the flight muscle and hydrolyzed to free fatty acid and glycerol. After penetrating the plasma membrane by an unknown mechanism, fatty acids are bound by the intracellular fatty acid binding protein (FABP) and transported through the cytosol. After their conversion to acyl-CoA esters, the fatty acids enter the mitochondrial matrix via the carnitine shuttle for subsequent β-oxidation. This article reviews the current knowledge of lipid metabolism in insect flight muscle, with particular emphasis on the structure and function of FABP and its expression during locust development and flight. 相似文献
9.
Stomatal transpiration is at the center of a crisis in water availability and crop production that is expected to unfold over the next 20 to 30 years. Global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture. Guard cell membrane transport is integral to controlling stomatal aperture and offers important targets for genetic manipulation to improve crop performance. However, its complexity presents a formidable barrier to exploring such possibilities. With few exceptions, mutations that increase water use efficiency commonly have been found to do so with substantial costs to the rate of carbon assimilation, reflecting the trade-off in CO2 availability with suppressed stomatal transpiration. One approach yet to be explored in detail relies on quantitative systems analysis of the guard cell. Our deep knowledge of transport and homeostasis in these cells gives real substance to the prospect for reverse engineering of stomatal responses, using in silico design in directing genetic manipulation for improved water use and crop yields. Here we address this problem with a focus on stomatal kinetics, taking advantage of the OnGuard software and models of the stomatal guard cell recently developed for exploring stomatal physiology. Our analysis suggests that manipulations of single transporter populations are likely to have unforeseen consequences. Channel gating, especially of the dominant K+ channels, appears the most favorable target for experimental manipulation.Stomata are pores that provide the major route for gaseous exchange across the impermeable cuticle of leaves and stems (Hetherington and Woodward, 2003). They open and close in response to exogenous and endogenous signals and thereby control the exchange of gases, most importantly water vapor and CO2, between the interior of the leaf and the atmosphere. Stomata exert major controls on the water and carbon cycles of the world (Schimel et al., 2001) and can limit photosynthetic rates by 50% or more when demand exceeds water supply (Ni and Pallardy, 1992). Stomatal transpiration is at the center of a crisis in water availability and crop production that is expected to unfold over the next 20 to 30 years; indeed, global water usage has increased 6-fold in the past 100 years, twice as fast as the human population, and is expected to double again before 2030, driven mainly by irrigation and agriculture (United Nations Educational, Scientific and Cultural Organization, 2009).Guard cell transport is integral to controlling stomatal aperture. Guard cells surround the stomatal pore and respond in a well-defined manner to an array of extracellular signals, including light, to regulate its aperture. Guard cells coordinate membrane transport within a complex network of intracellular signals (Willmer and Fricker, 1996; Blatt, 2000a, 2000b; Hetherington and Woodward, 2003; Shimazaki et al., 2007) to regulate fluxes, mainly of K+, Cl−, and malate, driving cell turgor and stomatal aperture. Our deep knowledge of these processes has made the guard cell the best known of plant cell models for membrane transport, signaling, and homeostasis (Willmer and Fricker, 1996; Blatt, 2000b; Roelfsema and Hedrich, 2010; Hills et al., 2012). This knowledge gives real substance to the prospect for reverse engineering of stomatal responses, using in silico design in directing genetic manipulation for improved crop yields, especially under water-limited conditions.Water use efficiency (WUE; defined as the amount of dry matter produced per unit of water transpired) is directly related to stomatal function. Thus, at the practical level, stomata represent an important target for breeders interested in manipulating crop performance. A large body of data relates stomata, transpiration, and carbon assimilation (Willmer and Fricker, 1996; Farquhar et al., 2001; Hetherington and Woodward, 2003; Lawson et al., 2011). Several examples illustrate how manipulating of stomatal characteristics can affect WUE (Fischer et al., 1998; Rebetzke et al., 2002; Masle et al., 2005; Eisenach et al., 2012). With few exceptions, however, mutations that increase WUE commonly do so at the expense of carbon assimilation, reflecting the trade-off in CO2 availability with suppressed stomatal transpiration.Stomatal movements generally lag behind short-term changes in available light associated with sunflecks and shadeflecks (Pearcy, 1990; Lawson et al., 2012; Lawson and Blatt, 2014). This hysteresis in response, between stomatal aperture and gas exchange on one hand and photosynthetic capacity on the other, can lead alternately to periods of assimilation limited by stomatal conductance, and of high transpiration without corresponding rates of assimilation (Lawson et al., 2011). It has been argued that such hysteresis in stomatal responsiveness with the demand for CO2 erodes assimilation and WUE, with substantial consequences for long-term yield (Vico et al., 2011; Eisenach et al., 2012; Lawson et al., 2012; Lawson and Blatt, 2014). If so, then improving WUE with gains in assimilation should be possible if the speed of stomatal responsiveness can be enhanced. However, the complexity of guard cell transport presents a formidable barrier to exploring such possibilities. Here we address this problem, taking advantage of OnGuard models of the stomatal guard cell. We explore in silico the potential for enhancing stomatal kinetics through single transporter (single gene product) manipulations. Our results identify the gating of the dominant K+ channels as the most promising target for experimental manipulation. 相似文献
10.
简单列举物质跨膜运输的几种方式,详细介绍通道转运中4种重要的通道:电位门通道、配体门通道、环核苷酸门通道和机械门通道及水通道概念的提出。总结通道易化扩散的特点。 相似文献
11.
Xylem Transport and the Negative Pressures Sustainable by Water 总被引:2,自引:0,他引:2
Experimental measurements of water's ability to sustain negativepressures are reviewed with special emphasis on the relevanceof the results to xylem transport. Results vary over severalorders of magnitude and depend on the conditions of testing.The greatest negative pressures are measured using heated, pressurizedwater or purified, degassed water. When conditions more closelyapproximating those found in biological systems are used, wateris considerably weaker. From these measurements, one can predictthe most likely range of negative pressures that can be sustainedin the xylem. This range is between -0·1 and -0·6MPa (absolute pressure). Negative pressures near -1 MPa arepossible, but require stringent conditions. Negative pressuresgreater than -2 MPa are also possible, but unlikely, based onthe experimental evidence.Copyright 1994, 1999 Academic Press Cavitation, embolism, negative pressure, xylem transport, Z-tube 相似文献
12.
13.
Donna Perkins-Balding Melanie Ratliff-Griffin Igor Stojiljkovic 《Microbiological reviews》2004,68(1):154-171
Acquisition of iron and iron complexes has long been recognized as a major determinant in the pathogenesis of Neisseria meningitidis. In this review, high-affinity iron uptake systems, which allow meningococci to utilize the human host proteins transferrin, lactoferrin, hemoglobin, and haptoglobin-hemoglobin as sources of essential iron, are described. Classic features of bacterial iron transport systems, such as regulation by the iron-responsive repressor Fur and TonB-dependent transport activity, are discussed, as well as more specific features of meningococcal iron transport. Our current understanding of how N. meningitidis acquires iron from the human host and the vaccine potentials of various components of these iron transport systems are also reviewed. 相似文献
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15.
Segments of the colon of anesthetized rats have been perfused in vivo with isotonic NaCl solutions and isotonic mixtures of NaCl and mannitol. Unidirectional and net fluxes of Na and Cl and the net fluxes of water and mannitol have been measured. Net water transport was found to depend directly on the rate of net Na transport. There was no water absorption from these isotonic solutions in the absence of net solute transport, indicating that water transport in the colon is entirely a passive process. At all NaCl concentrations studied, the lumen was found to be electrically negative to the surface of the colon by 5 to 15 mv. Na fluxes both into and out of the lumen were linear functions of NaCl concentration in the lumen. Net Na absorption from lumen to plasma has been observed to take place against an electrochemical potential gradient indicating that Na is actively transported. This active Na transport has been interpreted in terms of a carrier model system. Cl transport has been found to be due almost entirely to passive diffusion. 相似文献
16.
J. J. Oertli 《Physiologia plantarum》1966,19(3):809-817
There is no unanimous agreement about a definition of active water transport. The following definition was accepted: During an active transport or process, the water potential must increase and this gain must depend on the decrease in free energy in some metabolic process (5, 10). The passage of water from soil through plants to atmosphere can involve several active steps. A removal of solutes from the water represents a gain of osmotic water potential and this gain can exceed concurrent losses of other water potential components, resulting in a net gain of water potential. An increase of water potential was demonstrated in barley seedlings. Bleeding and guttation liquids were usually found to be more dilute than the external solution. Osmotic and gravitational potential components in exudates, thus, increased while other components remained virtually constant relative to the external solutions. The gain in osmotic potential depends most likely on a metabolic removal of salts: hence, the requirements for an active transport are satisfied. Active water transports, however, are not dependent or connected with the development of root pressure. The existence of active water transports disproves the rule that water flows only along water potential gradients (only against diffusion pressure deficit gradients). A gain in leaf water potential has a physiological significance since the range of soil water potentials a plant can withstand without wilting is extended. 相似文献
17.
18.
The Apparent Rates of Crossbridge Attachment and Detachment Estimated from Atpase Activity in Insect Flight Muscle
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The ATPase activity of single fibers of small fiber bundles (one to three fibers) of insect flight muscle was measured when fibers were repetitively released and restretched by 1.5% of their initial length. The ATPase activity increased with increasing duration of release-restretch pulses applied at a constant repetition frequency, reaching a maximum at a duration of ~20 ms. For a given duration, the average ATPase activity also increased with increasing frequency of applied length changes and reached a maximum (200% of the isometric ATPase) at a frequency of ~50 Hz. The data could be fitted to a two-state model in which the apparent rate of crossbridge detachment is enhanced when the crossbridges are mechanically released. Estimates of the apparent rates of attachment and detachment in the isometrically contracting state and of the enhanced detachment rate of unloaded crossbridges were derived from fits to the two-state model. After short pulses of releasing and restretching the fiber the force was low and increased after the restretch in a roughly exponential manner to the initial level. The rate at which force increased after a release-restretch pulse was similar to the sum of the apparent attachment and detachment rates for the isometrically contracting muscle derived from the ATPase activity measurements. 相似文献
19.
Graa Soveral Ana Madeira Maria C. Loureiro-Dias Teresa F. Moura 《Applied microbiology》2007,73(7):2341-2343
Intact yeast cells loaded with 5- and-6-carboxyfluorescein were used to assess water transport. The results were similar to those previously reported for protoplasts assessed by using either fluorescence or light scattering, and the activation energies were 8.0 and 15.1 kcal mol−1 (33.4 and 63.2 kJ mol−1) for a strain overexpressing AQY1 aquaporin and a parental strain, respectively. 相似文献
20.
The decision of the editors to solicit a review for the Medical Progress series of this journal devoted to current concepts of the renal handling of salt and water is sound in that this important topic in kidney physiology has recently been the object of a number of new, exciting and, in some instances, quite unexpected insights into the mechanisms governing sodium excretion. These developments have come about largely as a consequence of the fact that segments of nephrons previously inaccessible to direct study are now readily accessible.Many of the findings to be discussed argue for extensive revision of a number of our current widely held views concerning the renal handling of sodium chloride and water. In the opinion of the authors, the strength of this argument rests in the fact that many of these new findings were obtained under circumstances that enabled workers to gain more direct access to the nephron than has been possible heretofore. This is not to say that areas of controversy and disagreement no longer exist. Wherever possible, these have been identified. In attempting to provide a comprehensive review of this topic, it has been necessary at times to overgeneralize and to disregard minor deficiencies in some of the studies cited. Finally, we wish to emphasize that a considerable portion of the information contained herein derives from work still under active investigation. Much of this contemporary work will undoubtedly withstand the rigors of future experimental scrutiny. It is inevitable, however, as William James so aptly noted in the quotation cited below, that some of our present ideas will need to be abandoned or revised in favor of newer, more convincing evidence. Seen in this light, the present effort is intended as nothing more than a timely survey of this active and fertile topic in renal physiology. 相似文献