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  • 1975-1979  (5)
  • 1
    Electronic Resource
    Electronic Resource
    The influence of externally supplied sucrose on phloem transport in the maize leaf strip (1977)
    Springer
    Planta 137 (1977), S. 145-151 
    Details
    ISSN: 1432-2048
    Keywords: Phloem transport ; Sucrose ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Sucrose (2,5–1000 mmol l−1), labeled with [14C]sucrose, was taken up by the xylem when supplied to one end of a 30-cm-long leaf strip of Zea mays L. cv. Prior. The sugar was loaded into the phloem and transported to the opposite end, which was immersed in diluted Hoagland's nutrient solution. When the Hoagland's solution at the opposite end was replaced by unlabeled sucrose solution of the same molarity as the labeled one, the two solutions met near the middle of the leaf strip, as indicated by radioautographs. In the dark, translocation of 14C-labeled assimilates was always directed away from the site of sucrose application, its distance depending on sugar concentration and translocation time. When sucrose was applied to both ends of the leaf strip, translocation of 14C-labeled assimilates was directed toward the lower sugar concentration. In the light, transport of 14-C-labeled assimilates can be directed (1) toward the morphological base of the leaf strip only (light effect), (2) toward the base and away from the site of sucrose application (light and sucrose effect), or (3) away from the site of sucrose application independent of the (basipetal or acropetal) direction (sucrose effect). The strength of a sink, represented by the darkened half of a leaf strip, can be reduced by applying sucrose (at least 25 mmol l−1) to the darkened end of the leaf strip. However, equimolar sucrose solutions applied to both ends do not affect the strength of the dark sink. Only above 75 mmol l−1 sucrose was the sink effect of the darnened part of the leaf strip reduced. Presumably, increasing the sucrose concentration replenishes the leaf tissue more rapidly, and photosynthates from the illuminated part of the leaf strip are imported to a lesser extent by the dark sink.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00387551
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Synthesis of P-protein in mature phloem of Cucurbita maxima (1976)
    Springer
    Planta 132 (1976), S. 109-118 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Cotyledons of Cucurbita maxima Duch. seedlings were provided with 14C-labeled amino acids for 12 h. Besides the bulk of labeled amino acids the sieve-tube exudate also carried labeled proteins. 80% of the incorporated radioactivity was found in the P-protein, 20% in a neutral protein, and traces were found in acidic proteins after fractionation on diethyl-aminoethyl cellulose columns. The radioactive elutes were characterized by autoradiographs of both disc- and sodium dodecyl sulfate-gelelectropherograms, and by isoelectric focusing. The P-protein fraction appeared with the void volume from the diethylaminoethyl-cellulose column. Obviously, this is the protein that gels when oxidized and that is reversibly precipitable giving rise to filaments when processed for electron microscopy. Its main component has a molecular weight of 115,000 Dalton. By isoelectric focusing this fraction separated into 3 proteins with isoelectric points of 9.8, 9.4, and 9.2. The isoelectric point 9.2-protein probably is identical with an oligomer of a 30,000 Dalton protein with neutral isoelectric point, which keeps 20% of the incorporated label. Microautoradiographs suggest that the labeled proteins were synthesized in companion cells. The results indicate that P-protein of Cucurbita maxima is synthesized continuously in mature phloem. It can be assumed that P-protein has a relatively high turn-over rate. Therefore it seems unlikely that P-protein is a “structural” protein.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388891
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    The influence of light, darkness, and lack of CO2 on phloem translocation in detached maize leaves (1975)
    Springer
    Planta 122 (1975), S. 143-154 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Longitudinal strips from leaf blades of Zea mays L., with veins continuous along their whole length, proved to be a very uniform and convenient material for translocation experiments. Under normal photosynthetic conditions a very strong basipetal assimilate movement was shown. In the dark this movement persisted as long as starch reserves were available. Parts of the strips exposed to darkness or to CO2-free air, i.e. nonphotosynthetic conditions, became strong sinks which attracted assimilates, darkness having the strongest effect. Microradioautographs showed that transport of assimilates took place in the sieve tubes of the phloem.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00388654
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    The influence of externally applied organic substances on phloem translocation in detached maize leaves (1976)
    Springer
    Planta 132 (1976), S. 269-277 
    Details
    ISSN: 1432-2048
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Solutions of organic substances show differing influences on the direction of phloem transport of 14C-labeled assimilates in predarkened maize leaf strips, when externally applied to one end of the strip. One group of substances “pushes” the assimilates away from the site of application. Examples of this group are 75 mM solutions of sucrose, trehalose, maltose, D-glucose, D-fructose, glucose-6-phosphate, raffinose and galactose. There is strong evidence that “pushing” substances are taken up from the apoplast and loaded into the phloem. Another group of substances attracts the assimilates, it seems to “pull” the assimilates in direction to the site of application. Examples of this second group are 75 mM solutions of arabinose, melibiose, myo-inositol, D-mannitol, polyethylene glycol 2000, and Na2-EDTA (ethylene-diaminetetraacetate). The “pulling” substances obviously are not taken up into living cells. It is assumed that they accumulate in the apoplast and build up a water stress (water potential), which is counteracted by an increase of solute concentration in the parenchyma, thus creating a sink for assimilates. A third group of substances shows inert behaviour, having no perceptible influence on phloem transport, at least not, when applied as 75 mM solutions. At concentrations of more than 300 mM, inert substances tend to attract assimilates like those of the second group. Inert substances are xylose, sorbose, 2-deoxy-D-glucose, mannose and sorbitol.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00399726
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  • 5
    Electronic Resource
    Electronic Resource
    Das Experiment: Transport im Phloem (1975)
    Weinheim : Wiley-Blackwell
    Biologie in unserer Zeit 5 (1975), S. 26-28 
    Details
    ISSN: 0045-205X
    Keywords: Life and Medical Sciences
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/biuz.19750050105
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    Paper (German National Licenses)
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