Martinez, V., Ctro. Edafol. y Biol. Apl. Segura, CSIC, Apdo 4195, E-30080 Murcia, Spain
Bernstein, N., Inst. of Soils and Water, ARO, Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel
Läuchli, A., Dept. of Land, Air and Water Rsrc., Univ. of California, Davis, CA 95616, United States

Experiments with labeled phosphorus (32P) were carried out to study the effect of NaCl (80 mM) on transport of inorganic phosphorus (Pi) in the salt sensitive lettuce plant (Lactuca sativa L. cv. Black-seeded Simpson). The concentration of Pi used in all experiments was 0.1 mM. Salinity inhibited 32P uptake by the roots as well as translocation of 32P from root to shoot. When the plants were exposed for 3 h to a nutrient solution containing 32P, 80 mM NaCl reduced 32Pi translocation from root to shoot by 21%. This inhibition increased to 85% during a subsequent 3-h period in unlabeled solution. The concentration of 32P in leaves increased with decreasing leaf age regardless of the salinity level and leaf size. Indirect evidence supports the proposal that NaCl inhibits the retranslocation of Pi from old to young leaves. It is hypothesized that high levels of NaCl decrease the mobility of Pi stored in vacuoles and, as a result, inhibit export from this storage compartment to other parts of the plant.