1,479 research outputs found
3-O-methyl glucose uptake stimulation by auxin and by fusicoccin in plant materials and its relationships with proton extrusion
No full textAuxin and fusicoccin (FC) stimulate the active uptake of 3-O-methyl glucose (3-O-MG) in those materials in which they have been shown to activate an electrogenic proton extrusion (Pisum sativum L. stems, Zea mays L. coleoptiles and roots). In maize roots the curve relating 3-O-MG influx to external concentrations indicated that the values of the apparent Km increase in the 3-O-MG concentration range between 2×10-5 mol l-1 and 2×10-2 mol l-1. FC did not alter the Km values and its stimulating effect was nearly constant at all 3-O-MG concentrations tested. Basal and FC-induced uptake of 3-O-MG appeared associated with a transient proton influx suggesting that also in maize roots a sugar-proton contransport occurs. Diethyl stilbestrol, which inhibits proton extrusion, inhibited also basal and FC-induced 3-O-MG uptake. The data support the view that the stimulation by FC of 3-O-MG uptake is closely related to that of proton extrusion. The stimulation by FC of 3-O-MG uptake cannot be replaced by increasing extracellular proton concentration, nor may be explained only by the FC-induced hyperpolarization of transmembrane potential difference. The hypothesis is proposed that the effect of FC on 3-O-MG uptake depends on an increase of cytoplasmic pH, following the activation of the proton extruding system
Evidence for an active transport of methyl-α-D-glucopyranoside in pea stem segments
No full textThe nature of the transport of α-MG in pea internode segments has been investigated. α-MG uptake exhibits saturation kinetics. The transport of α-MG occurs against a concentration gradient and is inhibited by inhibitors of oxidative phosphorylation (FCCP and Antimycin A), indicating that an active process is involved in α-MG transport. This conclusion is in agreement with the finding that α-MG transport is strongly enhanced by fusicoccin which has been shown to stimulate several active transport processes in plant materials.The nature of the transport of α-MG in pea internode segments has been investigated. α-MG uptake exhibits saturation kinetics. The transport of α-MG occurs against a concentration gradient and is inhibited by inhibitors of oxidative phosphorylation (FCCP and Antimycin A), indicating that an active process is involved in α-MG transport. This conclusion is in agreement with the finding that α-MG transport is strongly enhanced by fusicoccin which has been shown to stimulate several active transport processes in plant materials
Bifurcations of piecewise smooth flows:perspectives, methodologies and open problems
No full textIn this paper the theory of bifurcations in piecewise smooth flows is critically surveyed. The focus is on results that hold in arbitrarily (but finitely) many dimensions, highlighting significant areas where a detailed understanding is presently lacking. The clearest results to date concern equilibria undergoing bifurcations at switching boundaries and limit cycles undergoing grazing and sliding bifurcations. After discussing fundamental concepts such as topological equivalence of two piecewise smooth systems, discontinuity-induced bifurcations are defined for equilibria and limit cycles. Conditions for equilibria to exist in n-dimensions are given, followed by the conditions under which they generically undergo codimension-one bifurcations. The extent of knowledge of their unfoldings is also summarized. Codimension-one bifurcations of limit cycles and boundary-intersection crossing are described together with techniques for their classification. Codimension-two bifurcations are discussed with suggestions for further study
Erratum to "The perception of emotion and social cues in faces" [Neuropsychologia 45 (2007) 1] (DOI:10.1016/j.neuropsychologia.2006.11.001)
No full text[Correction Notice: An erratum for this article was reported in Vol 45(10) of Neuropsychologia (see record 2007-06958-027). The publisher regrets that in the above referenced Guest Editorial, published in special issue 45/1: The perception of emotion and social cues in faces, one of the author names was represented incorrectly. The correct representation is M.I. Gobbini.
On necrocapitalism: A plague journal
No full textM.I. Asma is the collective designation for six authors from Canada and the United States, representing a variety of revolutionary anticapitalist theoretical persuasions: J. Moufawad-Paul, Devin Zane Shaw, Mateo Andante, Johannah May Black, Alyson Escalante, and D. W. Fairlane. As the pandemic transitioned from science fiction to reality in early 2020, a number of writers and thinkers in the imperialist metropoles declared the impossibility of writing in the face of a future that is foreclosed. And yet, due to the nightmare that capitalism has been since its beginning, numerous writers and thinkers from the margins have always written in the face of such foreclosure. Meanwhile, other contemporary thinkers sought to conceptualize the unfolding pandemic according to conceptions of bio/necropolitics, forgetting the foundation upon which these conceptions have always existed.
The M.I. Asma writing group came together to stake out a different terrain, thinking through the pandemic as events unfolded while also always working to think beyond the capitalist imaginary. Writing between April 2020 and May 2021, the authors set out to produce a serial theoretical philosophical project focused on class struggle in the midst of the COVID-19 pandemic. The authors approached the pandemic as an occasion to think capitalism according to what it always has been, what the pandemic reveals about its current ideological deployment, and how we can think about a communist alternative in the face of exterminism.
This book collects, with some revisions and with a new epilogue, the entries from the On Necrocapitalism blog, where M.I. Asma’s interventions first appeared.DC Author's celebration 202
Evidence for the coupling of proton extrusion to K+ uptake in pea internode segments treated in fusicoccin or auxin
No full textWhen pea internode segments are incubated in a K+-deficient medium, a rapid increase of K+ in the medium is observed in the first 3 h, followed by a progressive decrease in the following period. Fusicoccin (FC) and, to a much lesser extent, indole-3-acetic acid (IAA), increase the initial K+ outburst, while in the second phase they accelerate the reabsorption of K+. Since the initial K+ outburst takes place also if the segments are incubated in buffered solutions at progressively decreasing pH, its enhancement by FC is interpreted as a consequence of the acidification of the free space. Such an acidification makes available, for both uptake into the cells and diffusion into the medium, a consistent amount of the cations retained by non-exchangeable anions in the Donnan free space (DFS).
The proton extrusion promoted by FC or IAA is differentially affected by the presence of monovalent cations in the medium. K+ and to a lesser extent Na+ stimulate it while Cs+ and Li+ have little activity or inhibit the reaction. The order of activity of these ions roughly corresponds to their capacity to activate a K+ -activated ATPase present in “plasmalemma” preparations from pea internode segments. Dicyclohexycarbodiimide (DCCD), an inhibitor of K+-ATPases, also inhibits growth and proton extrusion.
If segments were partially depleted of the K+ in the DFS by preincubation with either growth-promoting substances or in acidic buffers, and then transferred into fresh medium, the FC- and IAA-promoted proton extrusion was strongly stimulated by the presence in the fresh medium of K+, while Na+ appeared much less active.
A satisfactory correlation between the stimulatory effect on proton extrusion and that on K+ uptake appears to exist even in the very first phase of treatment with FC, provided the segments are preincubated in buffers at pH 5. This treatment eliminates the initial K+ outburst that otherwise would mask the stimulation of K+ uptake. Under such conditions a proton extrusion/K+ uptake ratio close to unity was found
Effects of monovalent cations on IAA- and FC-stimulated proton-cation exchange in pea stem segments
No full text1.(1) At relatively low (1–10 mM) salt concentration in the medium, proton extrusion in normal, auxin (IAA)- and fusicoccin (FC)-treated pea internode segments is markedly stimulated by K+ and, at a lesser extent, by Rb+, while Na+ and other monovalent cations show little or no effect. At high (100 mM) concentration also Na+ stimulates H+ extrusion, and the effects of K+, Rb+ and Na+ become quantitatively similar. The stimulation of H+ extrusion by monovalent cations is clearly synergistic with the one induced by either IAA or FC.
2.(2) Both IAA and (much more) FC markedly enhance the rates of K+ and of Na+ uptake in pea internode segments. Both growth promoters strongly increase the selectivity of the uptake system for K+, as compared with Na+, at low but not at high salt concentrations. Under all conditions tested a qualitative correlation exists between K+ and Na+ uptake rate and the stimulating effect of these cations on proton extrusion. The cation uptake/titratable H+ extrusion ratio is decreased by either IAA or FC. The value of this ratio is always larger than 1, and increases with the increase of salt concentration in the medium. This may suggest that re-absorption and/or reassociation of an aliquot of extruded protons with extruded −OH or weak base mask a consistent fraction of the proton efflux. These results are consistent with the hypothesis that IAA and FC, although acting on different primary receptors, activate the same proton/monovalent cation antiport mechanism endowed with a high affinity for K+
Comparative study of British and Malaysian peat soils pertainting to geotechnical characteristics
No full textPeat soils occur in many countries and are described differently at times from both a qualitative and quantitative perspective. Peats are formed naturally through the decomposition of plant and animal matter under anaerobic conditions that take place over long periods of time. While the estimated and reported extent of Malaysian peat was approximately 2.6 million hectares respectively [12], there is an estimated 1.6 million hectares (minimum) of peat land available in British [6]. In British, peat soils are classified as Bog and Fen Peat. However in Malaysia, peat soil is described and generally termed as basin and valley peat [4]. The behaviour and composition of these peats are different from each other, accentuating the need for a useful engineering geological classification of peat soils. These soils are known for their low shear strength and high compressibility characteristics leading to unstable ground conditions. This paper focuses on comparative study an overview of the characteristic geotechnical properties for these soils. It also examines and discusses the effect of basic properties and behaviour of composition of each soil with case studies that had been done by one of the authors at Western Johore, Malaysia.Soft Soil
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