LAUSR

The Arabidopsis sensitive-to-freezing8 (sfr8) mutant exhibits reduced cell-wall (CW) fucose levels and compromised freezing tolerance. To examine whether CW fucosylation affects the response to desiccation also, we tested the effect of leaf excision in sfr8 and the allelic mutant mur1-1. Leaf water loss was strikingly higher than wild type in these, but not other, fucosylation mutants. We hypothesised that reduced fucosylation in guard cell (GC) walls might limit stomatal closure through altering mechanical properties. Multifrequency atomic force microscopy (AFM) measurements revealed a reduced elastic modulus (E'), representing reduced stiffness, in sfr8 GC walls. Interestingly, however, we discovered a compensatory mechanism whereby a concomitant reduction in the storage modulus (E'') maintained a wild type viscoelastic time response (tau) in sfr8. Stomata in intact leaf discs of sfr8 responded normally to a closure stimulus, ABA, suggesting the time response may relate more to closure properties than stiffness does. sfr8 stomatal pore complexes were larger than wild type and GCs lacked a fully developed cuticular ledge, both potential contributors to the greater leaf water loss in sfr8. We present data that indicate fucosylation-dependent dimerisation of the CW pectic domain rhamnogalacturonan-II may be essential for normal cuticular ledge development and leaf water retention.