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(American Journal of Botany. 2007;94:503-514.)
© 2007 Botanical Society of America, Inc.

Anatomy and Morphology

Pit membranes in tracheary elements of Rosaceae and related families: new records of tori and pseudotori1

Steven Jansen8,9, Yuzou Sano8, Brendan Choat, David Rabaey, Frederic Lens and Roland R. Dute

2Jodrell Laboratory, Royal Botanic Gardens, Kew, TW9 3DS, Richmond, Surrey, UK; 3Laboratory of Wood Biology, Graduate School of Agriculture, Hokkaido University, Sapporo 060-8589, Japan; 4Department of Viticulture and Enology, University of California, Davis, California 95616 USA; 5Laboratory of Plant Systematics, K.U.Leuven, Institute of Botany and Microbiology, Kasteelpark Arenberg 31, BE-3001 Leuven, Belgium; 7Department of Biological Sciences, 101 Life Sciences Building, Auburn University, Auburn, Alabama 36849 USA 6National Herbarium of the Netherlands, Leiden University Branch, P.O. Box 9514, NL-2300 RA Leiden, The Netherlands;

ABSTRACT

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 torus-like under the light microscope, observations by electron microscopy illustrate that they represent "pseudotori" 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). Vestured pits with homogenous pit membranes are reported for Hemiptelea (Ulmaceae). The homoplastic nature of pit membrane characteristics may be related to functional adaptations in terms of safety and efficiency of water transport or may reflect different developmental processes of xylem elements. These observations illustrate that there is more variation in angiosperm pits than previously thought.

Key Words: fiber • pit • pit membrane • pseudotorus • Rosaceae • Rosales • torus • tracheid






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