ABA signalling modulates the detection of the LM6 arabinan cell wall epitope at the surface of Arabidopsis thaliana seedling root apices

P>The hormonal and physiological regulations underpinning the cell contexts of structural features of the heterogeneous cell wall pectic polysaccharide rhamnogalacturonan-I are far from being understood. The effect of the modulation of abscisic acid (ABA) concentrations and sensitivity on the detection of the LM6 1,5-arabinan epitope at the surface of Arabidopsis thaliana seedling root apices was assessed by means of fluorescence imaging. Treatment with 50 nM ABA resulted in an increase in the detection of the LM6 epitope at the root surface in the region of the meristem. An inhibitor of ABA biosynthesis and introduction of the ABA synthesis mutation aba3-2 resulted in reduced epitope detection. The same ABA application resulted in an increase in the number of epidermal root meristem cells and both this and LM6 epitope detection were specifically disrupted in the abi4 ABA-insensitive mutant. These two effects were uncoupled with the application of higher ABA concentrations, which resulted in a reduction in the number of epidermal root meristem cells but increased LM6 epitope detection. This work demonstrates a role for ABI4-mediated ABA signalling in the modulation of pectic arabinan occurrence at the A. thaliana root meristem.