1,720,984 research outputs found
Effects of fusicoccin on K+ and Na+ net uptake in plant endowed with different K-Na selectivity.
No full textEffect of ethylene on auxin- and fusicoccin-induced growth of pea internode segments and on the secretion of H+ in the incubation medium
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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
Effects of a brassinosteroid on growth and on H+-extrusion in isolated radish cotyledons: comparison with the effects of benzyladenine
No full textWe investigated the effect of 24-epibrassinolide (BR) on the cytokinin-bioassay based on growth of isolated radish (Raphanus sativus L. cv. Tondo Rosso Quarantino) cotyledons. BR stimulated growth of the cotyledons by about 50% when applied at saturating concentrations (3 μM). This effect was much lower than that of saturating concentrations of benzyladenine (BA) which was about 150% at 10 μM BA. The effects of saturating concentrations of BR and BA were additive. BR, but not BA, stimulated H+-secretion by the cotyledons (measured as acidification of the incubation medium) slightly but reproducibly. These results indicate that the modes of action of the two phytoregulators are at least partially different. BR-induced stimulation of H+-secretion was of similar amplitude to that induced by a concentration of fusicoccin (30 nM) such as to stimulate growth to the same extent as BR. These results suggest that BR-induced stimulation of radish cotyledon growth might depend, at least in part, on BR-induced acidification of the wall space, similar to that observed on Azuki bean epicotyls and maize roots
Fusicoccin-induced, K+-stimulated proton secretion and acid-induced growth of apical root segments
No full text1. (1) Fusicoccin (FC) markedly stimulates proton secretion in isolated apical segments from pea, bean and maize roots. This effect of FC is already detectable after 1 min, and reaches a maximal rate approx. 10 min after the addition of the glucoside. 2. (2) FC-induced proton secretion is strongly stimulated by the presence in the medium of K+ (and not by that of Na+ or Li+) at concentrations higher than 2·10-4 M, while it is not significantly influenced by substitution of Cl- with the slowly penetrating SO4= or benzenesulfonate anions. Net K+ uptake is significantly stimulated by FC. 3. (3) Experiments of titration at constant pH in the range between pH 5.9 and 4 show that the rate of proton secretion in the absence of FC strongly depends on external pH. In contrast, FC-induced increase of the rate of proton extrusion appears very little affected by external pH in the same pH range. 4. (4) FC markedly stimulates elongation of the root segments. This effect is enhanced by the presence of K+ (but not of Na+ or Li+) in the medium. In the absence of FC low pH values of the medium strongly promote irreversible elongation of apical segments of maize roots. Maximal elongation rate is observed at pH 3.7. The effect of acid on elongation is consistently lesser than that of FC, and is not additive to it. The presence of K+ (and not of Na+) in the medium strongly increases FC-induced elongation at pH 6, while it has little effect at pH 3.7. These results are interpreted as indicating that FC stimulates in roots the same energy-dependent proton secretion mechanism previously shown to be activated by FC in stem, coleoptiles, leaves, cotyledons and embryos from dormant seeds. In roots, as in stem and coleoptiles, FC-induced stimulation of cell enlargement seems largely, but not completely explained by its capacity to decrease the pH in the cell wall space
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
Fusicoccin structure-activity relationships: stimulation of growth by cell enlargement and promotion of seed germination
No full textThe activity of a number of fusicoccin derivatives and analogues has been assayed on growth by cell enlargement and on proton extrusion in pea (Pisum sativum L, cv. Alaska) internode segments, on growth by cell enlargement in isolated squash (Cucurbita maxima Dechesne in Lam. variety Mantovana) cotyledons, and on germination of light-requiring lettuce (Lactuca sativa L. cv. Grand Rapids) and of abscisic acid-inhibited radish (Raphanus sativus L. variety Tondo Rosso Quarantino) seeds. A similar pattern of activity in the different tests was found for most fusicoccin derivatives and analogues. As with fusicoccin, the activity of its derivatives and analogues on growth of pea internodes is paralleled by the activity on the capability of the tissue to acidify the incubation medium. The obtained data are in full agreement with the view that the activity of fusicoccin on different physiological processes depends on its primary activation of a single system, involved in proton extrusion
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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