SALT-INDUCED INHIBITION OF PHOSPHORUS TRANSPORT IN LETTUCE PLANTS

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