An Examination of the Role of Silicate in Sodium Transport and Salinity Tolerance in Rice (Oryza sativa)

Silicate (Si)-mediated alleviation of salinity toxicity in rice is proposed to occur through a decrease in apoplastic sodium (Na+) transport. This is said to decrease shoot Na+ accumulation, a commonly proposed salt tolerance strategy. To investigate this, salt-tolerant (Pokkali) and salt-sensitive (IR29) rice cultivars were grown in 0 or 1.67 mM Si over a range of Na+ concentrations, and cultivar-specific effective concentrations of Na+ at which shoot fresh weight was decreased by 50% were determined. Within this experimental framework, salinity tolerance strategies were characterized using the radiotracer 24Na+ along with electrophysiological, photometric, and fluorescent dye measurements. Si treatment was found have no effect on transmembrane ion currents while decreasing shoot Na+ accumulation by over 50% in both cultivars. Si-treated IR29 exhibited lower apoplastic bypass and shoot Na+ flux. In Pokkali, examinations of Na+ influx, efflux, and shoot-to-root recirculation were unable to reconcile differences between shoot Na+ content and tracer-flux analyses.M.Sc