Characterization of Na⁺ exclusion mechanisms of salt‐tolerant reed plants in comparison with salt‐sensitive rice plants

Salt‐tolerant reed plants ( Phragmites communis Trinius) and salt‐sensitive rice plants ( Oryza sativa L. cv. Kinmaze) were grown in salinized nutrient solutions up to 50 m M NaCl, and growth, Na + contents and kinetics of 22 Na + uptake and translocation were compared between the species to characterize the salt tolerance mechanisms operating in reed plants. When both plants were grown under the same salinity, Na + contents of the shoots were lower in reed plants, although those of the roots were quite similar. The shoot base region of both species accumulated Na + more than the leaf blades did. Sodium‐22 uptake and pulse‐chase experiments suggested that the lower Na + transport rate from root to shoot could limit excessive Na + accumulation in the reed shoot. There was a possibility that the apparently lower 22 Na + transport rate to the shoot of reed plants was due to net downward Na + transport from shoot base to root.