Discrimination Between L- and D-arabinose Enantiomers by Arabidopsis thaliana: D-arabinose Inhibits Germination in the Dark and Induces Senescence
Anchors, Kristin T. and Harrington, Gregory N.
Department of Integrated Natural Sciences, Arizona State University, West Campus
The plant cell wall is a complex and dynamic structure in which the pectin polysaccharide composition is highly regulated. Amongst the many pectin sugars, L-arabinose content is known to undergo changes during plant development. Free D-arabinose is not detectable in plants but is characteristic of the cell wall of some plant pathogens. The purpose of this study was to characterize the phenotypic effects that L- and D-arabinose have on the germination, growth and development of the model plant species Arabidopsis thaliana. Seed were germinated on MS/agar media supplemented with L- or D- arabinose at a range of concentrations. In other experiments plants were transferred to these media after 14-day growth on sucrose media. D-arabinose was characterized as having more severe impacts on all aspects of growth and development at concentrations exceeding 0.5% than equivalent concentrations of L-arabinose. In germination studies, D-arabinose acts as an inhibitor in the dark, whereas L-arabinose has little impact. D-arabinose does not inhibit germination in the light but does impact growth and viability, rapidly killing seedlings. Two-week old seedlings transferred to 1.5% D-arabinose are inhibited from further growth after four days and eventually die. Biochemical characterization indicates anthocyanin accumulation precedes rapid chlorophyll degradation. Experiments indicate that D-arabinose is not acting as a competitive inhibitor of a key L-arabinose metabolic enzyme. These results suggest that Arabidopsis not only discriminates between the L- and D- enantiomers of arabinose but also may respond to D-arabinose as it would to a pathogen-related invasion. Current investigations are pursuing this hypothesis.