Quantifying contribution of SOS1 and GORK plasma membrane transporters towards salinity tolerance in barley by the MIFE technology

The relative contribution of SOS1 and GORK plasma membrane transporters towards salinity \tolerance in barley was quantified using the MIFE (microelectrode ion flux estimation) technique to screen 50 barley varieties for their ability to exclude sodium from uptake (e.g. the functional activity of SOS1 Na+/H+ exchanger) and to retain potassium in leaf mesophyll (functional activity of GORK channels). It was found that salt-sensitive varieties Gairdner, Naso Nijo, and ZUG403 showed relatively low (around -200 nmol m-2 s-1) rate of Na+ pumping, while salt-tolerant varieties ZUG293, Yerong and CPI showed 2.5 to 3 fold (the range of -500 to -600 nmol m-2 s-1) higher SOS1 Na+/H+ activity. Also, a 5-fold variability in the magnitude of net K+ efflux was found among barley accessions (flux range from -300 to -1600 nmol m-2 s-1). Minimal K+ leak (hence, the highest tissue tolerance) was measured in varieties CM72, Numar, YYXT and Yerong; all known to possess superior salinity stress tolerance. It is suggested that (1) salinity tolerance in barley is conferred by multiple physiological mechanisms operating via a range of plasma membrane and organelle transporters; (2) the MIFE technique may be used as an efficient screening tool to quantify the functional activity of key membrane transporters contributing to above traits. Furthermore, the MIFE technique may also be suitable for screening DH population for mapping genes conferring key physiological traits behind salinity tolerance in plants.