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  • 1975-1979  (4)
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Year
  • 1
    Electronic Resource
    Electronic Resource
    Ultrastructure of metaphloem sieve elements inZea mays (1975)
    Springer
    Protoplasma 83 (1975), S. 365-388 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Metaphloem sieve elements from various parts of the plant body ofZea mays L. were examined with the electron microscope. No qualitative differences were found among sieve elements from sources, sinks, and intermediate regions of the plant. At maturity all sieve elements are lined with a parietal layer of cytoplasm, consisting of a plasmalemma, an anastomosing network of endoplasmic reticulum (ER), occasional stacks of ER, mitochondria, and plastids with protein crystalloids. Many mature sieve elements contained persistent, although apparently degenerated nuclei. In addition, in many mature sieve elements the vacuoles apparently continued to be delimited from the parietal cytoplasm by the tonoplast. In most relatively uninjured sieve elements the plasmalemma-lined sieve-plate pores contained little callose and cytoplasmic components and, hence, were largely unoccluded. P-protein was not encountered in any sieve elements at any stage of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01418595
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  • 2
    Electronic Resource
    Electronic Resource
    Ultrastructure of minor veins inCucurbita pepo leaves (1975)
    Springer
    Protoplasma 83 (1975), S. 217-232 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The minor veins ofCucurbita pepo leaves were examined as part of a continuing study of leaf development and phloem transport in this species. The minor veins are bicollateral along their entire length. Mature sieve elements are enucleate and lack ribosomes. There is no tonoplast. The sieve elements, which are joined to each other by sieve plates, contain mitochondria, plastids and endoplasmic reticulum as well as fibrillar and tubular (190–195 Ā diameter) P-protein. Fibrillar P-protein is dispersed in mature abaxial sieve elements but remains aggregated as discrete bodies in mature adaxial sieve elements. In both abaxial and adaxial mature sieve elements tubular P-protein remains undispersed. Sieve pores in abaxial sieve elements are narrow, lined with callose and are filled with P-protein. In adaxial sieve elements they are wide, contain little callose and are unobstructed. The intermediary cells (companion cells) of the abaxial phloem are large and dwarf the diminutive sieve elements. Intermediary cells are densely filled with ribosomes and contain numerous small vacuoles and many mitochondria which lie close to the plasmalemma. An unusually large number of plasmodesmata traverse the common wall between intermediary cells and bundle sheath cells suggesting that the pathway for the transport of photosynthate from the mesophyll to the sieve elements is at least partially symplastic. Adaxial companion cells are of approximately the same diameter as the adaxial sieve elements. They are densely packed with ribosomes and have a large central vacuole. They are not conspicuously connected by plasmodesmata to the bundle sheath.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01282555
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  • 3
    Electronic Resource
    Electronic Resource
    Structure and development of sieve cells in the primary phloem ofPinus resinosa (1976)
    Springer
    Protoplasma 87 (1976), S. 27-37 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The primary phloem consists mostly of sieve cells. Procambial cells and very young sieve cells contain all the components characteristic of young nucleate cells. Increase in wall thickness, which is relatively limited, constitutes the first indication of sieve-cell differentiation. During the period of wall thickening, the plastids develop starch grains and then fibrillar inclusions. Eventually the internal lamellae of the plastids collapse. The plastids do not form crystalline inclusions. As the sieve cell approaches maturity, an extensive network of smooth, tubular endoplasmic reticulum (ER) appears and then becomes mostly parietal in distribution. At maturity, large aggregates of this ER occur at the sieve areas. These aggregates are interconnected longitudinally by the parietal network of ER. In addition to the ER, the mature, plasmalemma-lined primary sieve cell contains a degenerate nucleus, with intact nuclear envelope, plastids, and mitochondria. Dictyosomes, ribosomes, and vacuoles are lacking. P-protein is not present at any stage of development.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01623956
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  • 4
    Electronic Resource
    Electronic Resource
    Structure and development of sieve areas in the hypocotyl ofPinus resinosa (1975)
    Springer
    Protoplasma 84 (1975), S. 109-125 
    Details
    ISSN: 1615-6102
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The sieve areas inPinus resinosa consist of groups of plasmalemma-lined pores joined in the middle of the wall by large compound median cavities. Numerous membranes extend into the pores from aggregates of smooth, tubular endoplasmic reticulum opposite the sieve areas and merge in the median cavities. A compound median cavity arises through the union of smaller simple median cavities, each of which is initially associated with a single plasmodesma. Callose platelets were not associated with developing pores, but the pores of most fully-developed sieve areas were lined with callose. Sieve cells also have connections with albuminous cells. The connections on the sieve-cell side of the wall are similar to sieve-area pores, those on the albuminous-cell side to plasmodesmata. These connections also are associated with compound median cavities containing many membranes. The albuminous cells contain protoplasmic components similar to those of other parenchymatous cells including chloroplasts, cytoplasmic fibers, and microbodies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02075947
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