Salinity-induced ion flux patterns from the excised roots of Arabidopsis sos mutants

The SOS signal-transduction pathway is known to be important for ion homeostasis and salt tolerance in plants. However, there is a lack of in planta electrophysiological data about how the changes in signalling and ion transport activity are integrated at the cellular and tissue level. In this study, using the non- invasive ion flux MIFE technique, we compared net K+, H+ and Na+ fluxes from elongation and mature root zones of Arabidopsis wild type Columbia and sos mutants. Our results can be summarised as follows: ( 1) SOS mutations affect the function of the entire root, not just the root apex; ( 2) SOS signalling pathway is highly branched; ( 3) Na+ effects on SOS1 may by-pass the SOS2/SOS3 complex in the root apex; ( 4) SOS mutation affects H+ transport even in the absence of salt stress; ( 5) SOS1 mutation affects intracellular K+ homeostasis with a plasma membrane depolarisation-activated outward-rectifying K+ channel being a likely target; ( 6) H+ pump also may be a target of SOS signalling. We provide an improved model of SOS signalling and discuss physiological mechanisms underlying salt stress perception and signalling in plants. Our work shows that in planta studies are essential for understanding the functional genomics of plant salt tolerance.