Characteristics of Na+ and K+ absorption in Suaeda salsa (L.) Pall.

Suaeda salsa can grow well in saline soils with high sodium (Na)-low potassium (K) concentrations. While high Na accumulation in plant tissues plays an important role in osmoregulation and maintenance of water absorption for normal growth of Suaeda salsa, characteristics of Na and K absorption in S. salsa grown in such saline soils have not been elucidated. We thus examined Na and K absorption characteristics of S. salsa grown in nutrient solutions of graded sodium chloride (NaCl) with 1 mmol L-1 K or of graded potassium chloride (KCl) with 1 mmoI L-1 Na. The K accumulation capacity in S. salsa plant tissues was greater than the Na accumulation capacity. Although Na showed no competitive effects on K absorption, K application suppressed Na absorption drastically. Selectivity for K over Na in the absorption system became higher than that for Na over K concomitantly with increased Na or K concentration in the medium, indicating that Suaeda salsa is able to absorb K effectively with absorption of a large amount of Na. Sodium absorption was significantly decreased by tetraethylammonium (typical K channel inhibitor). Calcium (Ca) application increased not Na absorption but K absorption, resulting in enhancement of selectivity for K over Na. We speculate Na absorption pathways in S. salsa are partly mediated by AKT1 (Arabidopsis K transporter 1) type K channel and LCT (a low-affinity cation transporter) and NSCCs (non-selective cation channels) are not the major Na absorption pathway. These results may provide an explanation for the fact that S. salsa can grow well under saline soils with high Na-low K concentrations.