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Wide-band tracheids in genera of Portulacaceae: novel, non-xylary tracheids possibly evolved as an adaptation to water stress.

Authors
  • Landrum, James V
Type
Published Article
Journal
Journal of plant research
Publication Date
Sep 01, 2006
Volume
119
Issue
5
Pages
497–504
Identifiers
PMID: 16896531
Source
Medline
License
Unknown

Abstract

Wide-band tracheids (WBTs) are novel tracheids with wide, lignified secondary walls that intrude deeply into the cell lumen when viewed in transverse sections. These tracheids are found in a few genera in related families in the order Caryophyllales: Aizoaceae, Cactaceae, and Portulacaceae. WBTs in these three families vary in (1) systematic occurrence (found in more highly derived genera in each family), (2) location in plant organs, and (3) structure and dimensions. In addition, an analysis was conducted of WBT cell walls to test the hypothesis that WBTs evolved as an adaptation to water stress (i.e., the wide secondary walls should prevent collapse of the primary wall during water stress). The cell wall data show that primary cell walls in WBTs cannot inwardly collapse to occlusion, thus providing support for the water stress hypothesis of WBT evolution. With consideration of their systematic occurrence, the molecular phylogenetic data, and data here showing support for a water stress adaptive origin, it is logical to assume that WBTs evolved in genera that were adapting to environments undergoing a rapid trend toward aridification.

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