Sodium influx and accumulation in arabidopsis

Arabidopsis is frequently used as a genetic model in plant salt tolerance studies, however, its physiological responses to salinity remain poorly characterized. This study presents a characterization of initial Na⁺ entry and the effects of Ca²⁺ on plant growth and net Na⁺ accumulation in saline conditions. Unidirectional Na⁺ influx was measured carefully using very short influx times in roots of 12-d-old seedlings. Influx showed three components with distinct sensitivities to Ca²⁺, diethylpyrocarbonate, and osmotic pretreatment. Pharmacological agents and known mutants were used to test the contribution of different transport pathways to Na⁺ uptake. Influx was stimulated by 4-aminobutyric acid and glutamic acid; was inhibited by flufenamate, quinine, and cGMP; and was insensitive to modulators of K⁺ and Ca²⁺ channels. Influx did not differ from wild type in akt1 and hkt1 insertional mutants. These data suggested that influx was mediated by several different types of nonselective cation channels. Na⁺ accumulation in plants grown in 50 mM NaCl was strongly reduced by increasing Ca²⁺ activity (from 0.05-3.0 mM), and plant survival was improved. However, plant biomass was not affected by shoot Na⁺ concentration, suggesting that in Arabidopsis Na⁺ toxicity is not dependent on shoot Na⁺ accumulation. These data suggest that Arabidopsis is a good model for investigation of Na⁺ transport, but may be of limited utility as a model for the study of Na ⁺ toxicity.