Plasma-membrane electrical responses to salt and osmotic gradients contradict radiotracer kinetics, and reveal Na -transport dynamics in rice (Oryza sativa L.)

Abstract

A systematic analysis of NaCl-dependent, plasma-membrane depolarization (∆∆Ψ) in rice roots calls into question the current leading model of rapid membrane cycling of Na+ under salt stress. To investigate the character and mechanisms of Na+ influx into roots, Na+-dependent changes in plasma-membrane electrical potentials (∆∆Ψ) were measured in root cells of intact rice (Oryza sativa L., cv. Pokkali) seedlings. As external sodium concentrations ([Na+]ext) were increased in a step gradient from 0 to 100 mM, membrane potentials depolarized in a saturable manner, fitting a Michaelis–Menten model and contradicting the linear (non-saturating) models developed from radiotracer studies. Clear diffe..