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

• Published in: American journal of botany Vol. 94; no. 4; p. 503
• Main Authors: Jansen, Steven, Sano, Yuzou, Choat, Brendan, Rabaey, David
• Format: Journal Article
• Language: English
• Published: Columbus Botanical Society of America, Inc 01-04-2007
• Subjects: Botany; Flowers & plants; Membranes; Scanning electron microscopy
• ISSN: 0002-9122; 1537-2197

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 stnctures are tons-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 stncture. Pseudotori are occasionally found in few Elaeagnaceae and Rhamnaceae and appear to be related to species with fiber-tracheids and/or tracheids. Tne 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. [PUBLICATION ABSTRACT]