ibclogo XVI International Botanical Congess


Abstract Number: 4731
Poster No. = 1725


EFFECTS OF ENVIRONMENTAL STRESSES ON THE EXPRESSION OF WIDE-BAND TRACHEIDS IN ANACAMPSEROS (PORTULACACEAE)


Vic Landrum, Biology Department, Washburn University, Topeka, Kansas, USA


Wide-band tracheids (WBTs) are found in leaves and stems of species in the South African genus Anacampseros (Portulacaceae). Wide-band tracheids are parenchyma cells that are converted into modified tracheids with wide secondary walls intruding into the lumen. In stems WBTs occupy rays and pith, and are thought to function as an alternative water-conduction system or water-storage system in severe water-stress conditions common to their location. Experiments were conducted to determine the environmental variables that initiate WBT formation. Seedlings of Anacampseros rufescens, A. lanceolata, and A. ustulata were subjected to varying watering, lighting, nutritional, and temperature regimes. Tissues were harvested and processed at 30 and 60 days. Cell diameter, lumen diameter, wide-band thickness, and percent of cell area were measured. Light intensity was the variable controlling expression of WBTs. Seedlings at low light (2000 lux) showed significantly smaller and narrower WBTs compared full-light seedlings (20,000 lux). Water-stressed plants showed a slight increase in wide-band thickness, but neither nutritionally-stressed nor temperature-stressed plants showed any significant difference in WBTs structure. The hypothesis that WBTs are initiated to serve primarily as water-conductors in water-stress conditions is not supported by these experiments.


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