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  • 1
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    Intervascular pit membranes with a torus in the wood of Ulmus (Ulmaceae) and related genera (2004)
    In:  New Phytologist vol. 163, pp. 51-59
    Details
    Publication Date: 2024-01-12
    Description: \xe2\x80\xa2 The distribution of intervascular pit membranes with a torus was investigated in juvenile wood samples of 19 species of Ulmus and seven related genera.\n\xe2\x80\xa2 A staining solution of safranin and alcian blue (35 : 65) was recommended to distinguish torus-bearing pit membranes using light microscopy.\n\xe2\x80\xa2 Intervascular pit membranes connecting relatively wide vessel elements resembled those of most angiosperms, as they were of uniform thickness. By contrast, bordered pit pairs with round to oval pit apertures and indistinct pit canals that connected narrow (incomplete) vessel elements or vascular tracheids with distinct helical thickenings were frequently characterized by a torus in ring-porous wood samples of Ulmus and Zelkova. Tori were lacking in diffuse-porous species of Ampelocera, Aphananthe, Gironniera, Holoptelea, Phyllostylon, Trema and Ulmus.\n\xe2\x80\xa2 Our observations suggest that tori are more common in cold temperate climates than in warm (sub)tropical environments. This may indicate that narrow tracheary elements with torus-bearing pit membranes provide an auxiliary conducting system which is of low conductivity, but offers greater resistance to freezing-induced cavitation.
    Keywords: Ulmus (elm) ; Ulmaceae ; pit membrane ; torus ; pit structure ; wood anatomy ; tracheary elements
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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  • 2
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    A comparative ultrastructural study of pit membranes with plasmodesmata associated thickenings in four angiosperm species (2008)
    In:  Protoplasma vol. 33, pp. 255-262
    Details
    Publication Date: 2024-01-12
    Description: Recent micromorphological observations of angiosperm pit membranes have extended the number and range of taxa with pseudo-tori in tracheary elements. This study investigates at ultrastructural level (TEM) the development of pseudo-tori in the unrelated Malus yunnanensis, Ligustrum vulgare, Pittosporum tenuifolium, and Vaccinium myrtillus in order to determine whether these plasmodesmata associated thickenings have a similar developmental pattern across flowering plants. At early ontogenetic stages, the formation of a primary thickening was observed, resulting from swelling of the pit membrane in fibre-tracheids and vesselelements. Since plasmodesmata appear to be frequently, but not always, associated with these primary pit membrane thickenings, it remains unclear which ultrastructural characteristics control the formation of pseudo-tori. At a very late stage during xylem differentiation, a secondary thickening is deposited on the primary pit membrane thickening. Plasmodesmata are always associated with pseudo-tori at these final developmental stages. After autolysis, the secondary thickening becomes electron-dense and persistent, while the primary thickening turns transparent and partially or entirely dissolves. The developmental patterns observed in the species studied are similar and agree with former ontogenetic studies in Rosaceae, suggesting that pseudo-tori might be homologous features across angiosperms.
    Keywords: ontogeny ; pseudo-torus ; tracheary element ; pit membrane ; bordered pit ; wood ultrastructure
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
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  • 3
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    Micromorphology and systematic distribution of pit membrane thickenings in Oleaceae: Tori and pseudo-tori (2008)
    In:  IAWA Journal vol. 29 no. 4, pp. 409-424
    Details
    Publication Date: 2024-01-12
    Description: Recent studies on the functional significance of pit membranes in water conducting cells have renewed general interest in their micromorphology. At least two types of pit membrane thickenings have been described in angiosperm families, i.e. genuine tori and pseudo-tori. This study explores the distribution and morphology of pit membrane thickenings in 69 species and 23 genera within Oleaceae using light and electron microscopy. Torus-bearing pit membranes are confirmed for Osmanthus, and new records are reported for Chionanthus retusa, Picconia azorica, and P. excelsa, but not for the other species studied of Chionanthus. This infrageneric variation suggests that tori represent a plastic feature that has evolved more than once within the family as the result of functional adaptation to efficient and safe water transport. Pseudo-tori are observed in species of Abeliophyllum, Fontanesia, Forsythia, Jasminum, Ligustrum, Menodora, and Syringa. Based on structural differences, we state that tori and pseudo-tori can be distinguished as non-homologous features.
    Keywords: electron microscopy ; pit aperture ; pit membrane ; plasmodesmata ; pseudo-torus ; torus ; tracheid ; vessel element
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 4
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    Pit membranes in tracheary elements of Rosaceae and related families: New records of tori and pseudotori (2007)
    In:  Proceedings of the National Academy of Sciences of the United States of America vol. 94 no. 4, pp. 503-514
    Details
    Publication Date: 2024-01-12
    Description: The micromorphology of pits in tracheary elements was examined in 35 species representing 29 genera of Rosaceae and related families to evaluate the assumption that angiosperm pits are largely invariant. In most Rosaceae, pit membranes between fibers and tracheids frequently appear to have amorphous thickenings with an irregular distribution. Although these structures are toruslike under the light microscope, observations by electron microscopy illustrate that they represent \xe2\x80\x98\xe2\x80\x98pseudotori\xe2\x80\x99\xe2\x80\x99 or plasmodesmata-associated thickenings. These thickenings frequently extend from the periphery of the pit membrane and form a cap-like, hollow structure. Pseudotori are occasionally found in few Elaeagnaceae and Rhamnaceae and appear to be related to species with fiber-tracheids and/or tracheids. True tori are strongly associated with round to oval pit apertures and are consistently present in narrow tracheary elements of Cercocarpus (Rosaceae), Planera (Ulmaceae), and ring-porous species of Ulmus and Zelkova (Ulmaceae). \nVestured pits with homogenous pit membranes are reported for Hemiptelea (Ulmaceae). The homoplasticnature of pit membrane characteristics may be related to functional adaptations in terms of safety and efficiency of water transportor may reflect different developmental processes of xylem elements. These observations illustrate that there is more variation in angiosperm pits than previously thought.
    Keywords: fiber ; pit ; pit membrane ; pseudotorus ; Rosaceae ; Rosales ; torus ; tracheid
    Repository Name: National Museum of Natural History, Netherlands
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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