R. Ehwald - Academia.edu (original) (raw)
Papers by R. Ehwald
Biochemie und Physiologie der Pflanzen, 1989
Plant Science, 2000
Suspension cells of Dioscorea deltoidea Wall (strain D-1) were maintained in a semicontinuous cul... more Suspension cells of Dioscorea deltoidea Wall (strain D-1) were maintained in a semicontinuous culture (SCC) in shake flasks at a high growth rate. It was shown that continuous propagation growth of this culture is unstable on Murashige's and Skoog's (MS) medium due to P starvation. On a P-enriched MS-medium the SCC was stable even at mean specific growth rates \ 0.3 day − 1. Highest volumetric concentrations of furostanol glycosides were obtained, when a P-enriched SCC was not further subcultivated but fed with sucrose. The investigated culture is able to control phosphate uptake and to prevent toxicity on media with excess P. High concentrations of cellular P i did not effect the ratio of furostanol to starch.
Annals of Botany, 2005
Background and Aims Water adhesion forces, water absorption capacity and permeability of the pine... more Background and Aims Water adhesion forces, water absorption capacity and permeability of the pine exine were investigated to consider a possible function of sporopollenin coatings in the control of water transport. Methods The experiments were carried out with sporopollenin capsules obtained from pine pollen consisting of an empty central capsule and two sacci. Changes in the concentration of excluded dextran molecules in the medium were analysed to quantify water absorption by purified exine fragments and the osmotic volume flow out of the intact central capsule. Key Results The contact angle of sporopollenin to water is higher than the one to ethanol and lower than the one to n-heptane. The water-filled pore space in pine sporopollenin amounts to only 20Á6 % of the matrix volume. A monosaccharide was excluded from 15 % and a trisaccharide from about 38 % of this space. Shrinkage of the central capsule induced by permeable osmotica was transient, whereas that induced by sodium polyacrylate (2100 g mol À1) was stable. Values obtained for the hydraulic conductance L P of the exine (0Á39-0Á48 mm s À1 MPa À1) are comparable in size to those of biomembranes. Sodium sulfate solutions induced a significant osmotic flow through the exine (reflection coefficient at least 0Á6). The exine around the central capsule can be ruptured by equilibration of its lumen with a concentrated electrolyte solution and subsequent transfer to water. The denatured protoplast along with the intact intine was ejected when pollen grains were subjected to this osmotic shock treatment. Conclusions The pine exine is easily wetted with water and does not represent a significant barrier to water exchange either liquid or gaseous. Through osmotic burst, it can be separated from the intine. The effect of salts and small solute molecules on water fluxes may be functionally significant for rehydration upon pollination.
Functional Plant Biology, 2010
Effects of relatively small changes of hydrostatic and osmotic pressure on root exudation were st... more Effects of relatively small changes of hydrostatic and osmotic pressure on root exudation were studied with maize (Zea mays L.) plants grown in hydroculture to estimate the root reflection coefficient for the applied osmolyte (PEG 600). During the first seconds after a change in hydrostatic pressure, the exudation rate measured with a microflow sensor was instantaneously and strongly changed due to elastic deformation of the metaxylem vessels in the branched part of the main root axis. In osmotic experiments, a time of 10–20 s was required before the maximum change of the exudation rate was recorded. This retardation can be explained by diffusive saturation of the non-agitated root surface film and radial turgor propagation. A new standing osmotic gradient was reached within 4 min after a change of the water potential difference (osmotic, hydrostatic). The steady-state exudation rate J was altered by osmotic and hydrostatic forces with nearly equal efficiencies when branch roots wer...
Journal of Experimental Botany, 1995
The total volume of the free space (FS) and the external film (EF) outside the cell wall of livin... more The total volume of the free space (FS) and the external film (EF) outside the cell wall of living plant materials was determined as partition volumes of sugars and dextran, respectively. Sugar uptake and kinetics of FS and EF saturation were recorded polarimetrically. The FS equilibrates within 20 s in suspension culture of Chenopodium album L. Here, the free apoplastic volume (FAV), i.e. the difference between sugar and dextran partition volumes, was determined by short-term partitioning of fructose and dextran in samples containing the plant material and an optically compensated (non-rotating) solution of both components. The selective partitioning of the sugar with the FAV causes an increase in optical activity, which is dependent on the FAV. The FAV of a suspension cultured biomass was found to be correlated with the percentage volume of dead cells. The volume originating by plasmolysis between cell wall and plasma membrane was measured as an increase of the FAV. In seedling ro...
Gematologiâ i transfuziologiâ, 1988
II. Internationales Symposium Ökologie und Physiologie des Wurzelwachstums
Microbiology, 1995
ABSTRACT Localization of immobilized cells of the yeast Saccharomyces cerevisiae in the particles... more ABSTRACT Localization of immobilized cells of the yeast Saccharomyces cerevisiae in the particles of a carrier derived from the duckweed Wolffia arrhiza was studied by scanning electron microscopy. Yeast cells were generally immobilized inside the carrier particles, which consisted of cell-wall frameworks and remained cell-structured after protoplasm extraction. Moreover, the carrier particles made from W. arrhiza retained morphological and anatomic structure typical of the intact plant. This ensures a high degree of compartmentalization and, hence, efficient immobilization of yeast cells. These particles were shown to contain various morphological structures, providing for entry, compartmentalization, and exit of yeast cells. The described carrier particles are suggested as models for studying compartmentalization of symbiotic microorganisms in plant tissues.
Vesicle chromatography, a recently developed method for separation of biomolecules, uses the vesi... more Vesicle chromatography, a recently developed method for separation of biomolecules, uses the vesicular packing (VP) material (clusters of microcapsules derived from plant cells), which was tested with respect to its application for the recombinant protein separation. Since VP has a well-defined separation limit, biomolecules are distributed in two separate peaks: large molecules are excluded and small molecules permeate through cell walls into the empty cell lumen. Recombinant proteins frequently form oligomers, which differ from monomers not only in size but also chemically and biologically. In the present study, separations of the recombinant proinsulin fusion protein oligomer and monomer, the recombinant human gamma-interferon monomer and dimer and recombinant tumour necrosis factor-alpha were investigated. For peak identification, the fractions and starting samples of the recombinant proteins were analysed by HPLC. The separations occurred without any sorption effects and with h...
Biochemie und Physiologie der Pflanzen
Summary Transport and metabolism of 2-deoxy-D-glucose (2-deG) have been investigated in young mai... more Summary Transport and metabolism of 2-deoxy-D-glucose (2-deG) have been investigated in young maize seedlings. 2-deG taken up from the medium is phosphorylated by the cells of root tips and by the isolated scutellum and is largely transformed to a β -fructoside that is analogous to sucrose. In comparison with the whole content of soluble 2-deG- containing compounds in the tissues the portion of free 2-deG is small. 2-deG given to the scutellum of isolated embryos quickly participates in the reaction of the synthesis of sucrose and is rapidly transported as 2-deoxy-D-glucose- β -fructoside via phloem to the attraction centres of the root and the shoot. “2-deoxy-sucrose” and 2-deG-P are chiefly accumulated in the root tip. The use of 2-deG for the investigation of long distance transport of carbohydrates in higher plants is discussed.
Biochemie und Physiologie der Pflanzen
Summary 1. The uptake of monosaccharides by isolated maize root tips was found to be a function o... more Summary 1. The uptake of monosaccharides by isolated maize root tips was found to be a function of substrate concentration. It shows typical “dual isotherm” as they are well known with regard to the kinetics of ion uptake by plant tissues. 2. The “apparent free space” (FS) of isolated root tips was determined to be the distribution space of the disaccharide melibiose. The initial rates of sugar diffusion in the FS were calculated by the FS-volume and the “half time” of melibiose saturation of the FS. 3. Comparing the intensity of the absorption of sugars as of ions as well by plant tissues with the inital rates that might to be expected, when substrate diffusion takes place in the FS we saw that in the range of concentration from 10−5 to 10−3 M the diffusion rates are essentially less than the intensivities of uptake. 4. By this paper we come to the conclusion, that the function of saturation in the low range of concentration (mechanism 1 according to E pstein ) corresponds to the uptake mediated by carriers on the extern surface of the tissue, whilst the concentration function of the rate of absorption with higher substrate concentrations (> 1 mM) is also determined by the diffusion of the substrate to cell layers that lie behind the surface of the tissue. Therefore we conclude that at the uptake of ions, sugars, and of other substrates by plant tissues the “dual-hyperbolic isotherms” cannot be considered as a sign of several transport mechanisms with regard to cellular basis.
Journal of Chromatography A, 1992
The encapsulation and fractionated release of nucleic acids on vesicular packing (VP) materials h... more The encapsulation and fractionated release of nucleic acids on vesicular packing (VP) materials have been investigated. The earlier described dependence of the permeation of nucleic acid molecules through the vesicle membranes on the salt concentration is a necessary precondition for both encapsulation and fractionation. Encapsulation is achieved by applying a suitable sample onto a VP column that has been equilibrated with a high-salt buffer. In that buffer the sample molecules are permeable. Immediately after sample application, elution is started with a low-salt buffer, from which the sample molecules are excluded. At the front between the two buffers the permeability changes, and some of the sample molecules distributed inside the vesicles cannot pass through the membranes. These encapsulated molecules can be released by increasing the salt concentration in the eluent. If the encapsulated nucleic acid sample is polydisperse, a stepwise or linear increase in the salt concentration leads to a fractionated release. The fractions obtained differ in their molecular size composition.
Russian Journal of Plant Physiology, 1999
Beiträge zur Infusionstherapie = Contributions to infusion therapy
Permselect particles consisting of purified plant cell wall ghosts obtained from the biomass of a... more Permselect particles consisting of purified plant cell wall ghosts obtained from the biomass of a suspension culture of Chenopodium album L. show a very high efficiency for leukocyte binding. A package containing 1 g dry Permselect eliminates 99-100% of leukocytes from 80 ml of fresh blood, preserved whole blood, or red blood cell concentrates. At comparable conditions Permselect shows a higher efficiency of leukocyte binding than commercial filter material (cotton, cellulose acetate). The vitality parameter of filtered erythrocytes and their stability during storage were not altered. The data are discussed with respect to causality of leukocyte binding to the pectin-containing surface of the cell wall particles.
Die fortgeschrittene Miniaturisierung mikroelektronischer und mikrosystemtechnischer Bauteile erm... more Die fortgeschrittene Miniaturisierung mikroelektronischer und mikrosystemtechnischer Bauteile ermöglicht bereits heute die Entwicklung neuartiger medizin-und biotechnologischer Systeme, die durch hohen Tragekomfort für den Patienten und verminderte Analysekosten gekennzeichnet sind. Insbesondere auf dem Gebiet der point-of-care Diagnostik, die die gesundheitsrelevanten Daten des Patienten in der unmittelbaren Lebensumgebung und nicht notwendigerweise in der Arztpraxis ermittelt, werden sog. biomedical microelectromechanical systems (BioMEMS) breite Anwendung finden. Wir berichten über einen kontinuierlich messenden Glucosesensor, der bei der Blutzuckerkontrolle von Diabetikern Anwendung finden soll. Der Sensor funktioniert nach dem Prinzip der Affinitätsviskosimetrie [1] und ist als Mikroviskosimeter ausgeführt. Bei dem genutzten Nachweisprinzip erfolgt keine stoffliche Umsetzung der Glucose, sondern lediglich deren Affinitätsbindung an das pflanzliche Protein Concanavalin A (Con A). Dabei wird eine sensorische Flüssigkeit aus Con A und Dextran mit der im Körpergewebe befindlichen Glucose ins Gleichgewicht gesetzt, wodurch sich aufgrund des unterschiedlichen Vernetzungsgrades je nach Glucosekonzentration verschiedene Viskositäten einstellen, s. Fig. 1. Das Mikroviskosimeter wird dabei als integriertes MEMS in einer 0,25 µm BiCMOS-Technologie gefertigt.
Journal of Experimental Botany, 1985
The effect of phloem ringing on the uptake and transport of potassium by the roots of 4 week old ... more The effect of phloem ringing on the uptake and transport of potassium by the roots of 4 week old sunflower plants has been investigated. Ringing caused a rapid decline in both K+ uptake and its transport (86Rb tracer) to the shoot. The rate of root elongation and the levels of sucrose in the root showed parallel decreases after ringing. Measurement on isolated roots indicated that the effect of ringing the stem on K+ uptake by the roots was confined to the apical 10 mm that included the extension zone. It is postulated that the decline in potassium uptake and transport, brought about by ringing, is due to the severance of the sucrose supply which stops root growth.
Tripartite sporopollenin microcapsules prepared from pine pollen (Pinus sylvestris L. and Pinus n... more Tripartite sporopollenin microcapsules prepared from pine pollen (Pinus sylvestris L. and Pinus nigra Arnold) were analysed with respect to the permeability of the different strata of the exine which surround the gametophyte and form the sacci. The sexine at the surface of the sacci is highly permeable for polymer molecules and latex particles with a diameter of up to 200 nm, whereas the nexine covering the gametophyte is impermeable for dextran molecules, with a Stokes’ radius ≥4 nm (Dextran T 70), and for the tetravalent anionic dye Evans Blue (Stokes’ radius = 1·3 nm). The central capsules obtained by dissolution of the sporoplasts showed strictly membrane‐controlled exchange of non‐electrolytes, with half‐equilibration times in the range of minutes (monosaccharides, oligosaccharides) to hours (dextran molecules with Stokes’ radii up to 2·5 nm). The dependence of the permeability coefficients of the nexine for non‐electrolytes on Stokes’ radius or molecular weight shows that the ...
Biochemie und Physiologie der Pflanzen, 1989
Plant Science, 2000
Suspension cells of Dioscorea deltoidea Wall (strain D-1) were maintained in a semicontinuous cul... more Suspension cells of Dioscorea deltoidea Wall (strain D-1) were maintained in a semicontinuous culture (SCC) in shake flasks at a high growth rate. It was shown that continuous propagation growth of this culture is unstable on Murashige's and Skoog's (MS) medium due to P starvation. On a P-enriched MS-medium the SCC was stable even at mean specific growth rates \ 0.3 day − 1. Highest volumetric concentrations of furostanol glycosides were obtained, when a P-enriched SCC was not further subcultivated but fed with sucrose. The investigated culture is able to control phosphate uptake and to prevent toxicity on media with excess P. High concentrations of cellular P i did not effect the ratio of furostanol to starch.
Annals of Botany, 2005
Background and Aims Water adhesion forces, water absorption capacity and permeability of the pine... more Background and Aims Water adhesion forces, water absorption capacity and permeability of the pine exine were investigated to consider a possible function of sporopollenin coatings in the control of water transport. Methods The experiments were carried out with sporopollenin capsules obtained from pine pollen consisting of an empty central capsule and two sacci. Changes in the concentration of excluded dextran molecules in the medium were analysed to quantify water absorption by purified exine fragments and the osmotic volume flow out of the intact central capsule. Key Results The contact angle of sporopollenin to water is higher than the one to ethanol and lower than the one to n-heptane. The water-filled pore space in pine sporopollenin amounts to only 20Á6 % of the matrix volume. A monosaccharide was excluded from 15 % and a trisaccharide from about 38 % of this space. Shrinkage of the central capsule induced by permeable osmotica was transient, whereas that induced by sodium polyacrylate (2100 g mol À1) was stable. Values obtained for the hydraulic conductance L P of the exine (0Á39-0Á48 mm s À1 MPa À1) are comparable in size to those of biomembranes. Sodium sulfate solutions induced a significant osmotic flow through the exine (reflection coefficient at least 0Á6). The exine around the central capsule can be ruptured by equilibration of its lumen with a concentrated electrolyte solution and subsequent transfer to water. The denatured protoplast along with the intact intine was ejected when pollen grains were subjected to this osmotic shock treatment. Conclusions The pine exine is easily wetted with water and does not represent a significant barrier to water exchange either liquid or gaseous. Through osmotic burst, it can be separated from the intine. The effect of salts and small solute molecules on water fluxes may be functionally significant for rehydration upon pollination.
Functional Plant Biology, 2010
Effects of relatively small changes of hydrostatic and osmotic pressure on root exudation were st... more Effects of relatively small changes of hydrostatic and osmotic pressure on root exudation were studied with maize (Zea mays L.) plants grown in hydroculture to estimate the root reflection coefficient for the applied osmolyte (PEG 600). During the first seconds after a change in hydrostatic pressure, the exudation rate measured with a microflow sensor was instantaneously and strongly changed due to elastic deformation of the metaxylem vessels in the branched part of the main root axis. In osmotic experiments, a time of 10–20 s was required before the maximum change of the exudation rate was recorded. This retardation can be explained by diffusive saturation of the non-agitated root surface film and radial turgor propagation. A new standing osmotic gradient was reached within 4 min after a change of the water potential difference (osmotic, hydrostatic). The steady-state exudation rate J was altered by osmotic and hydrostatic forces with nearly equal efficiencies when branch roots wer...
Journal of Experimental Botany, 1995
The total volume of the free space (FS) and the external film (EF) outside the cell wall of livin... more The total volume of the free space (FS) and the external film (EF) outside the cell wall of living plant materials was determined as partition volumes of sugars and dextran, respectively. Sugar uptake and kinetics of FS and EF saturation were recorded polarimetrically. The FS equilibrates within 20 s in suspension culture of Chenopodium album L. Here, the free apoplastic volume (FAV), i.e. the difference between sugar and dextran partition volumes, was determined by short-term partitioning of fructose and dextran in samples containing the plant material and an optically compensated (non-rotating) solution of both components. The selective partitioning of the sugar with the FAV causes an increase in optical activity, which is dependent on the FAV. The FAV of a suspension cultured biomass was found to be correlated with the percentage volume of dead cells. The volume originating by plasmolysis between cell wall and plasma membrane was measured as an increase of the FAV. In seedling ro...
Gematologiâ i transfuziologiâ, 1988
II. Internationales Symposium Ökologie und Physiologie des Wurzelwachstums
Microbiology, 1995
ABSTRACT Localization of immobilized cells of the yeast Saccharomyces cerevisiae in the particles... more ABSTRACT Localization of immobilized cells of the yeast Saccharomyces cerevisiae in the particles of a carrier derived from the duckweed Wolffia arrhiza was studied by scanning electron microscopy. Yeast cells were generally immobilized inside the carrier particles, which consisted of cell-wall frameworks and remained cell-structured after protoplasm extraction. Moreover, the carrier particles made from W. arrhiza retained morphological and anatomic structure typical of the intact plant. This ensures a high degree of compartmentalization and, hence, efficient immobilization of yeast cells. These particles were shown to contain various morphological structures, providing for entry, compartmentalization, and exit of yeast cells. The described carrier particles are suggested as models for studying compartmentalization of symbiotic microorganisms in plant tissues.
Vesicle chromatography, a recently developed method for separation of biomolecules, uses the vesi... more Vesicle chromatography, a recently developed method for separation of biomolecules, uses the vesicular packing (VP) material (clusters of microcapsules derived from plant cells), which was tested with respect to its application for the recombinant protein separation. Since VP has a well-defined separation limit, biomolecules are distributed in two separate peaks: large molecules are excluded and small molecules permeate through cell walls into the empty cell lumen. Recombinant proteins frequently form oligomers, which differ from monomers not only in size but also chemically and biologically. In the present study, separations of the recombinant proinsulin fusion protein oligomer and monomer, the recombinant human gamma-interferon monomer and dimer and recombinant tumour necrosis factor-alpha were investigated. For peak identification, the fractions and starting samples of the recombinant proteins were analysed by HPLC. The separations occurred without any sorption effects and with h...
Biochemie und Physiologie der Pflanzen
Summary Transport and metabolism of 2-deoxy-D-glucose (2-deG) have been investigated in young mai... more Summary Transport and metabolism of 2-deoxy-D-glucose (2-deG) have been investigated in young maize seedlings. 2-deG taken up from the medium is phosphorylated by the cells of root tips and by the isolated scutellum and is largely transformed to a β -fructoside that is analogous to sucrose. In comparison with the whole content of soluble 2-deG- containing compounds in the tissues the portion of free 2-deG is small. 2-deG given to the scutellum of isolated embryos quickly participates in the reaction of the synthesis of sucrose and is rapidly transported as 2-deoxy-D-glucose- β -fructoside via phloem to the attraction centres of the root and the shoot. “2-deoxy-sucrose” and 2-deG-P are chiefly accumulated in the root tip. The use of 2-deG for the investigation of long distance transport of carbohydrates in higher plants is discussed.
Biochemie und Physiologie der Pflanzen
Summary 1. The uptake of monosaccharides by isolated maize root tips was found to be a function o... more Summary 1. The uptake of monosaccharides by isolated maize root tips was found to be a function of substrate concentration. It shows typical “dual isotherm” as they are well known with regard to the kinetics of ion uptake by plant tissues. 2. The “apparent free space” (FS) of isolated root tips was determined to be the distribution space of the disaccharide melibiose. The initial rates of sugar diffusion in the FS were calculated by the FS-volume and the “half time” of melibiose saturation of the FS. 3. Comparing the intensity of the absorption of sugars as of ions as well by plant tissues with the inital rates that might to be expected, when substrate diffusion takes place in the FS we saw that in the range of concentration from 10−5 to 10−3 M the diffusion rates are essentially less than the intensivities of uptake. 4. By this paper we come to the conclusion, that the function of saturation in the low range of concentration (mechanism 1 according to E pstein ) corresponds to the uptake mediated by carriers on the extern surface of the tissue, whilst the concentration function of the rate of absorption with higher substrate concentrations (> 1 mM) is also determined by the diffusion of the substrate to cell layers that lie behind the surface of the tissue. Therefore we conclude that at the uptake of ions, sugars, and of other substrates by plant tissues the “dual-hyperbolic isotherms” cannot be considered as a sign of several transport mechanisms with regard to cellular basis.
Journal of Chromatography A, 1992
The encapsulation and fractionated release of nucleic acids on vesicular packing (VP) materials h... more The encapsulation and fractionated release of nucleic acids on vesicular packing (VP) materials have been investigated. The earlier described dependence of the permeation of nucleic acid molecules through the vesicle membranes on the salt concentration is a necessary precondition for both encapsulation and fractionation. Encapsulation is achieved by applying a suitable sample onto a VP column that has been equilibrated with a high-salt buffer. In that buffer the sample molecules are permeable. Immediately after sample application, elution is started with a low-salt buffer, from which the sample molecules are excluded. At the front between the two buffers the permeability changes, and some of the sample molecules distributed inside the vesicles cannot pass through the membranes. These encapsulated molecules can be released by increasing the salt concentration in the eluent. If the encapsulated nucleic acid sample is polydisperse, a stepwise or linear increase in the salt concentration leads to a fractionated release. The fractions obtained differ in their molecular size composition.
Russian Journal of Plant Physiology, 1999
Beiträge zur Infusionstherapie = Contributions to infusion therapy
Permselect particles consisting of purified plant cell wall ghosts obtained from the biomass of a... more Permselect particles consisting of purified plant cell wall ghosts obtained from the biomass of a suspension culture of Chenopodium album L. show a very high efficiency for leukocyte binding. A package containing 1 g dry Permselect eliminates 99-100% of leukocytes from 80 ml of fresh blood, preserved whole blood, or red blood cell concentrates. At comparable conditions Permselect shows a higher efficiency of leukocyte binding than commercial filter material (cotton, cellulose acetate). The vitality parameter of filtered erythrocytes and their stability during storage were not altered. The data are discussed with respect to causality of leukocyte binding to the pectin-containing surface of the cell wall particles.
Die fortgeschrittene Miniaturisierung mikroelektronischer und mikrosystemtechnischer Bauteile erm... more Die fortgeschrittene Miniaturisierung mikroelektronischer und mikrosystemtechnischer Bauteile ermöglicht bereits heute die Entwicklung neuartiger medizin-und biotechnologischer Systeme, die durch hohen Tragekomfort für den Patienten und verminderte Analysekosten gekennzeichnet sind. Insbesondere auf dem Gebiet der point-of-care Diagnostik, die die gesundheitsrelevanten Daten des Patienten in der unmittelbaren Lebensumgebung und nicht notwendigerweise in der Arztpraxis ermittelt, werden sog. biomedical microelectromechanical systems (BioMEMS) breite Anwendung finden. Wir berichten über einen kontinuierlich messenden Glucosesensor, der bei der Blutzuckerkontrolle von Diabetikern Anwendung finden soll. Der Sensor funktioniert nach dem Prinzip der Affinitätsviskosimetrie [1] und ist als Mikroviskosimeter ausgeführt. Bei dem genutzten Nachweisprinzip erfolgt keine stoffliche Umsetzung der Glucose, sondern lediglich deren Affinitätsbindung an das pflanzliche Protein Concanavalin A (Con A). Dabei wird eine sensorische Flüssigkeit aus Con A und Dextran mit der im Körpergewebe befindlichen Glucose ins Gleichgewicht gesetzt, wodurch sich aufgrund des unterschiedlichen Vernetzungsgrades je nach Glucosekonzentration verschiedene Viskositäten einstellen, s. Fig. 1. Das Mikroviskosimeter wird dabei als integriertes MEMS in einer 0,25 µm BiCMOS-Technologie gefertigt.
Journal of Experimental Botany, 1985
The effect of phloem ringing on the uptake and transport of potassium by the roots of 4 week old ... more The effect of phloem ringing on the uptake and transport of potassium by the roots of 4 week old sunflower plants has been investigated. Ringing caused a rapid decline in both K+ uptake and its transport (86Rb tracer) to the shoot. The rate of root elongation and the levels of sucrose in the root showed parallel decreases after ringing. Measurement on isolated roots indicated that the effect of ringing the stem on K+ uptake by the roots was confined to the apical 10 mm that included the extension zone. It is postulated that the decline in potassium uptake and transport, brought about by ringing, is due to the severance of the sucrose supply which stops root growth.
Tripartite sporopollenin microcapsules prepared from pine pollen (Pinus sylvestris L. and Pinus n... more Tripartite sporopollenin microcapsules prepared from pine pollen (Pinus sylvestris L. and Pinus nigra Arnold) were analysed with respect to the permeability of the different strata of the exine which surround the gametophyte and form the sacci. The sexine at the surface of the sacci is highly permeable for polymer molecules and latex particles with a diameter of up to 200 nm, whereas the nexine covering the gametophyte is impermeable for dextran molecules, with a Stokes’ radius ≥4 nm (Dextran T 70), and for the tetravalent anionic dye Evans Blue (Stokes’ radius = 1·3 nm). The central capsules obtained by dissolution of the sporoplasts showed strictly membrane‐controlled exchange of non‐electrolytes, with half‐equilibration times in the range of minutes (monosaccharides, oligosaccharides) to hours (dextran molecules with Stokes’ radii up to 2·5 nm). The dependence of the permeability coefficients of the nexine for non‐electrolytes on Stokes’ radius or molecular weight shows that the ...