Developmental and Structural Section
Jahdi, Alexa , Marks, Carolyn , Hayden, W. John .
Intact perforation membranes in secondary xylem of the Acalypha virginica complex (Euphorbiaceae).
Annual stems of weedy temperate zone species of Acalypha become modestly woody by the end of their growing season. Structure of the few mm of secondary xylem formed in mature woody stems of three closely related species, A. deamii, A. rhomboidea, and A. virginica, is described based on study via LM, SEM, and laser scanning confocal microscopy (LSCM). Vessels are evenly dispersed as solitary or grouped cells bearing alternate intervascular pits and (mostly) ordinary simple perforations. Libriform fibers are thin-walled and non-septate. Rays are mostly uniseriate with a preponderance of upright cells. Axial parenchyma consists of rare paratracheal cells. In addition to ordinary simple perforations, a wide range of anomalous structures are frequently encountered: wide partial bars in vertical or horizontal orientation, thin partial bars that may be straight or curved, irregularly branched bars, and loops or discs of secondary wall material seemingly suspended in the perforation aperture. SEM and LSCM reveal anomalous “perforations” to retain intact membranes. It is hypothesized that retention of perforation membranes permits the enzyme complexes that synthesize secondary wall to wander into the “perforation” region, depositing the anomalous structures observed which are consequently interpreted as common motifs of secondary wall structure. Potential functional significance of intact perforation membranes in conjunction with ordinary simple perforations in the water conduction system as adaptations to drought stress is discussed.
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1 - University of Richmond, Department of Biology, Richmond, VA, 23173, USA
2 - University of Richmond, Department of Biology, 28 Westhampton Way, Richmond, Virginia, 23173, USA
xylem structure and function
Presentation Type: Oral Paper:Papers for Sections
Date: Monday, July 28th, 2008
Time: 10:00 AM