Sodium partitioning within the shoot of soybean

Abstract

Uptake and partitioning of Na + and Cl − in plants of soybean ( Glycine max L. Merr. cv. Hodgson) exposed to moderate NaCl concentrations were studied over an 8‐day period. Plants showed marked retention of Na + in the stems and low transport to laminae of young leaves. The xylem sap ascending the main axis was progressively depleted in Na + . The oldest leaf greatly contributed to Na + depletion of the sap flowing to younger leaves. These results in combination with estimates of phloem recirculation indicated that Na + accumulation in the young leaf was prevented both by depletion of Na + from the xylem stream, and by a high recirculation of Na + via the phloem. However, this protection of young leaves was effective only for very mild salinity treatment.