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  • 1
    Electronic Resource
    Electronic Resource
    Proton extrusion in seed coats of Phaseolus vulgaris L. (1985)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 8 (1985), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract. The present investigations were designed to identify proton pumps in seed coats of Phaseolus vulgaris L. Vacated seed-coat halves were exposed to bathing solutions with indicators for proton pump action and the pH changes in the media were measured. Fusicoccin increased the rate of proton extrusion from the seed coats. Orthovanadate and abscisic acid retarded the proton extrusion evoked by fusicoccin. Abolition of the proton extrusion by parachloromercuriphenylsulphonic acid was partially reversed by diethioerythritol. The extrusion was stimulated by high osmolarities (100 mol m−3 sorbitol), potassium ions (100 mol m−3 KCI) and light. Old seed coats reacted more rapidly to fusicoccin treatments than young ones. Proton pumping in seed coats and cotyledons showed differential responses to fusicoccin, K+ and sucrose. In contrast to seed coats, medium acidification by cotyledons was prohibited by addition of sucrose. The significance of proton pumps for photosynthate transfer in vivo is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3040.1985.tb01203.x
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  • 2
    Electronic Resource
    Electronic Resource
    Does light-promoted export from Commelina benghalensis leaves result from differential light-sensitivity of the cells in the mesophyll-to-sieve tube path? (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Physiologia plantarum 67 (1986), S. 0 
    Details
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: In contrast to the light-promoted uptake by mesophyll cells, light slightly inhibited sucrose uptake by stripped leaf disks of Commelina benghalensis L. This phenomenon appeared to result from a light-promoted vein-associated release, as light stimulated photosynthate release from stripped disks and inhibited that from mesophyll cells. In the -presence of the resorption-blocker p-chloromercuriphenylsulfonic acid, (PCMBS) the release of preloaded [14C]-sugars (sucrose, glucose) and [14C]-amino acids (alanine, asparagine, proline, valine, α-aminoisobutyric acid) from stripped disks was doubled in the light. Illumination enhanced by 20 to 60% the release of endogenous leaf cell compounds (sucrose, H2PO-4, K+, Mg2+, Ca2+) from stripped disks in the presence of PCMBS. Light also increased the export of [14C]-assimilates from intact leaves by 20% after pulse-labelling with 14CO2. A model for loading is proposed, based on the differential light sensitivities of the plasma membranes in the mesophyll-to-sieve tube path.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1399-3054.1986.tb02448.x
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  • 3
    Electronic Resource
    Electronic Resource
    Symplastic isolation of the sieve element-companion cell complex in the phloem of Ricinus communis and Salix alba stems (1991)
    Springer
    Planta 183 (1991), S. 69-76 
    Details
    ISSN: 1432-2048
    Keywords: Iontophoresis ; Phloem translocation ; Ricinus ; Salix ; Sieve element-companion cell complex ; Symplastic isolation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The anatomical and physiological isolation of the sieve element-companion cell complex (se-cc complex) was investigated in stems of Ricinus communis L. and Salix alba L. In Ricinus, the plasmodesmatal frequencies were in the proportions 8∶1∶2∶30, in the order given, at the interfaces between sieve tube-companion cell, sieve tube-phloem parenchyma cell, companion cellphloem parenchyma cell, and phloem parenchyma cellphloem parenchyma cell. The membrane potentials of the se-cc complex and the surrounding phloem-parenchyma cells sharply contrasted: the membrane potential of the se-cc complex was about twice as negative as that of the phloem parenchyma. Lucifer Yellow CH injected into the sieve element or into the companion cell remained within the se-cc complex. Dye introduced into phloem parenchyma only moved (mostly poorly) to other phloem-parenchyma cells. The distribution of the plasmodesmatal frequencies, the differential dye-coupling and the sharp discontinuities in membrane potentials indicate that the se-cc complexes constitute symplast domains in the stem phloem. Symplastic autonomy is discussed as a basic necessity for the functioning of the se-cc complex in the stem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00197569
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  • 4
    Electronic Resource
    Electronic Resource
    A three-step screening procedure to identify the mode of phloem loading in intact leaves (1993)
    Springer
    Planta 192 (1993), S. 31-39 
    Details
    ISSN: 1432-2048
    Keywords: Companion cell types ; Leaf (source-sink relations) ; Minor-vein configuration ; Phloem loading (apoplasmic, symplasmic) ; Plasmodesmatal continuity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A three-step screening method was developed to identify the mode of phloem loading in intact leaves. Phloem loading of 14CO2-derived photosynthate was challenged by p-chloromercuribenzenesulfonic acid (PCMBS) in leaves of dicotyledons with either a symplasmic (type 1, with intermediary cells as companion cells) or apoplasmic (type 2b, with transfer cells as companion cells) minor-vein configuration. Firstly, photosynthate export as the result of phloem loading was measured by collection of phloem exudate from the petiole. The PCMBS had virtually no effect on photosynthate export in representatives of type-1 families (Lamiaceae, Lythraceae, Onagraceae, Saxifragaceae). In contrast, photosynthate export was strongly reduced by PCMBS in representatives of type-2b families (Asteraceae, Balsaminaceae, Dipsacaceae, Linaceae, Tropaeolaceae, Valerianaceae) and type-2b members of polytypical families (Fabaceae, Scrophulariaceae). Secondly, densitometric measurements of leaf autoradiographs demonstrated that the contrast between the mesophyll and the lower-order veins was hardly affected by PCMBS treatment in type-1 species, whereas PCMBS strongly reduced the contrast in type-2b species. Thirdly, separate 14C-radioassays of vein and mesophyll tissues confirmed this observation. The three-step procedure thus revealed a strong and consistent reduction of phloem loading by PCMBS in type-2b species which was absent in type-1 species. In conclusion, phloem loading in type-2b species occurs via the apoplast and type-1 species execute an alternative — most likely symplasmic — mode of phloem loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00198689
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  • 5
    Electronic Resource
    Electronic Resource
    Different ratios of sucrose/raffinose-induced membrane depolarizations in the mesophyll of species with symplasmic (Catharanthus roseus, Ocimum basilicum) or apoplasmic (Impatiens walleriana, Vicia faba) minor-vein configurations (1996)
    Springer
    Planta 199 (1996), S. 185-192 
    Details
    ISSN: 1432-2048
    Keywords: Galactosyl oligosaccharides ; Membrane depolarization ; Phloem loading (apoplasmic, symplasmic) ; Raffinose uptake ; Sucrose uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract In mesophyll cells of species with a symplasmic (Ocimum basilicum, Catharanthus roseus, Magnolia denudata) or an apoplasmic (Vicia faba, Impatiens walleriana, Bellis perennis) minor-vein configuration, membrane depolarizations in response to 20 or 200 mol·m−3 raffinose and sucrose were measured. Ageing period and resting potential marginally affected the degree of depolarization. The symplasmic species showed similar depolarization responses to 20 and 200 mol·m−3 sucrose or raffinose. In the apoplasmic species, depolarization increased statistically significantly from 20 to 200 mol·m−3 sucrose, whereas the depolarization response to raffinose was equal at both concentrations. In the apoplasmic species, moreover, the depolarization response to raffinose was significantly weaker than to sucrose at all concentrations. A major difference between symplasmic and apoplasmic species seems to lie in the scantiness of raffinose carriers in the mesophyll plasma membrane of species with the apoplasmic mode of phloem loading.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00196558
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  • 6
    Electronic Resource
    Electronic Resource
    Effects of temperature on the conformation of the endoplasmic reticulum and on starch accumulation in leaves with the symplasmic minor-vein configuration (1994)
    Springer
    Planta 194 (1994), S. 443-453 
    Details
    ISSN: 1432-2048
    Keywords: Endoplasmic reticulum ; Intermediary cell ; Plasmodesma ; Symplasmic phloem loading ; Temperature sensitivity (phloem loading)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The phloem-loading-related effects of temperature on leaf ultrastructure were studied in seven species having numerous plasmodesmatal connections between the mesophyll and phloem (symplasmic minor-vein configuration). The response to temperature (between 5 and 30 °C) was characterized by drastic changes in the endoplasmic-reticulum labyrinth (ER labyrinth) of intermediary cells, in the position of the vacuole in bundle-sheath cells, and in the starch content in the chloroplasts of bundle-sheath cells and mesophyll cells. At temperatures above 20 °C, the ER system in the intermediary cells reached its maximal volume, while the vacuole in bundlesheath cells was positioned centripetally (proximal to the intermediary cell). With decreasing temperature, the ER labyrinth in intermediary cells gradually contracted till the ER was fully collapsed at 10 °C and the vacuole in bundle-sheath cells moved to a more centrifugal position. The apparent elimination of photosynthate transport via the ER and plasmodesmata at temperatures lower than 10 °C led to starch accumulation in the chloroplasts of bundle-sheath cells and mesophyll cells. All of these changes were fully temperature-reversible and probably reflect changes in the balance between photosynthate transport and storage. The ultrastructural shifts appear to be correlated with the passage of photosynthate through the intermediary cells and, as a consequence, with the rate of phloem loading at various temperatures. A contraction of the ER/plasmodesmata system imposed by cytoskeletal reorganisation is discussed as the reason for the blockage of phloem loading at low temperatures in association with the general chilling sensitivity of these species.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00714455
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  • 7
    Electronic Resource
    Electronic Resource
    Symplasmic connections between sieve element and companion cell in the stem phloem ofVicia faba L. have a molecular exclusion limit of at least 10 kDa (1997)
    Springer
    Planta 201 (1997), S. 195-201 
    Details
    ISSN: 1432-2048
    Keywords: Fluorescent dextran ; Intracellular microinjection ; Molecular exclusion limit ; Pore/plasmodesma unit ; Sieve element/companion cell complex ; Vicia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract High-molecular-weight fluorochromes were intracellularly injected into a sieve element of the fascicular stem phloem ofVicia faba L., using a modified membrane-potential-recording pressure probe. After stabilization of the membrane potential following microelectrode impalement, either LYCH (Lucifer Yellow CH), 4.4-kDa FITC-dextran (fluoresceinisothiocyanate-dextran) conjugate, or 3-kDa, 10-kDa or 40-kDa LYCH-dextran conjugate was microinjected into the sieve element. Longitudinal fluorochrome movement across the sieve plates and lateral displacement to the companion cells was detected with all the probes except the 40-kDa conjugate. This indicates that the molecular exclusion limit of the pore/plasmodesma units between a sieve element and a companion cell in the fascicular stem phloem ofVicia faba lies between 10 kDa and 40 kDa.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01007704
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  • 8
    Electronic Resource
    Electronic Resource
    Light-promoted diffusional amino acid efflux from Commelina leaf disks (1981)
    Springer
    Planta 152 (1981), S. 115-123 
    Details
    ISSN: 1432-2048
    Keywords: Amino acids, efflux and uptake ; Commelina ; Light and amino-acid efflux ; Phloem loading
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The release (=the measured loss) of amino acids was studied in Commelina benghalensis leaf disks. The release is assumed to be the result of influx and efflux, therefore, both movements were investigated. The uptake of 14C-labeled valine exhibited a biphasic isotherm. The uptake was pH-dependent, especially at low substrate concentrations (pH optimum 4.8). Signals for amino acid/proton co-transport were observed: stimulation of the uptake by fusicoccin (FC), inhibition by diethylstilbestrol (DES) or by high K+ concentrations. In the light, the ATP level of the disks was maintained during the uptake period (2 h), in darkness the ATP content decreased from 87 to 24 nmol g−1 fr. wt. However, light-promoted uptake, which is explained in the proton pump concept by an intensified proton extrusion as the result of high ATP production, was lacking. The release of amino acids was increased by washing with p-chloromercuriphenyl sulphonic acid (PCMBS), nystatin, 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), or KCN. The release (Q10 about 1.5) was independent of the external pH and was linearly related to the intracellular amino acid concentration. Light enhanced the rate of release to the same extent at all intracellular concentrations. The present results suggest that the release is balanced by a, at least partially, proton-driven influx and a diffusional ligh-promoted efflux. A provisional model shows how the diffusional effulx can be indirectly controlled by a counter-flow fueled by the metabolism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00391182
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  • 9
    Electronic Resource
    Electronic Resource
    Analysis of valine uptake by Commelina mesophyll cells in a biphasic active and a diffusional component (1982)
    Springer
    Planta 155 (1982), S. 335-341 
    Details
    ISSN: 1432-2048
    Keywords: Amino acid uptake ; Commelina ; Mesophyll cell ; Valine uptake
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Valine uptake by isolated Commelina benghalensis L. mesophyll cells was measured over a wide concentration range (10-6–4·10-2 mol l-1). The uptake data were subjected to iterative fitting. Experiments with carbonyl cyanide mchlorophenyl hydrazone (CCCP), diethylstilbestrol (DES), and p-chloromercuriphenylsulphonic acid (PCMBS) provided evidence that the biphasic uptake kinetics of valine consists of a diffusional component and a biphasic active uptake. The data from the control experiments, were also best fitted to one diffusional component and two Michaelis-Menten systems. The presence of two carrier systems in the plasmalemma, however, was considered to be virtual for the following reasons: (1) Both phases of active uptake were equally decreased by high concentrations of K+-ions. (2) Fusicoccin stimulated the active uptake in both phases to the same extent. (3) Inhibitors of the proton-driven uptake (CCCP, DES, PCMBS) similarly inhibited the active uptake at all concentrations. (4) The active uptake equally responded in both phases to changes in the pH. (5) Light also promoted the active uptake over the whole concentration range. These results strongly indicate that, despite its biphasic character, the active uptake is due to one proton-driven carrier system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00429461
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  • 10
    Electronic Resource
    Electronic Resource
    Microelectrode-recorded development of the symplasmic autonomy of the sieve element/companion cell complex in the stem phloem ofLupinus luteus L. (1994)
    Springer
    Planta 192 (1994), S. 165-175 
    Details
    ISSN: 1432-2048
    Keywords: Cellular ontogeny ; Lupinus ; Membrane potential ; Phloem translocation ; Sieve element/companion cell complex ; Symplasmic (dis)continuity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract From the cambial stage onwards, the symplasmic autonomy of sieve element/companion cell complexes (SE/CC-complexes) was followed in stems ofLupinus luteus L. by microinjection techniques. The membrane potential and the symplasmic autonomy of the mature SE/CC-complex was measured in successive internodes. A microelectrode was inserted into SE/CC-complexes or phloem parenchyma cells (PPs) and, after stabilization of the membrane potential, the membrane-impermeant fluorescent dye Lucifer Yellow CH (LYCH) was injected intracellullary. The plasmodesmata of the cambial SE/ CC precursor were gradually shut off at all interfaces beginning at the walls to be transformed into sieve plates. In the course of maturation, symplasmic discontinuity was maintained at the longitudinal walls of the complex. In the transverse walls of the SE, wide sieve pores were formed giving rise to longitudinal multicellular symplasmic domains of SE/CC-complexes. Symplasmic isolation of the files of mature SE/CC-complexes was demonstrated in several ways: (i) the membrane potential of the SE/CC-complexes (between -100 mV and -130 mV) was consistently more negative than that of the PPs (between-50 and -100 mV), (ii) No exchange of LYCH was observed between SE/CC-complexes and the PPs. Lucifer Yellow CH injected into the SEs exclusively moved to the associated CCs and to other SE/CC-complexes whereas LYCH injected into the PPs was only displaced to other PPs. (iii) The electrical coupling ratio between adjacent PPs was ten times higher than that between SE/CC-complex and PP. A gradient in the membrane potential of the SE/CC-complexes along the stem was not conclusively demonstrated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01089031
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