Ion balance and nitrogen metabolism responses of old leaves of rice seedlings under salt stress. Under salt stress, old leaves accumulates much higher concentrations of Na+, Cl− and NO3− than young leaves. Under salt stress, up-regulation of OsHKT1;1, OsHAK10 and OsHAK16 advances the accumulation of Na+ in old leaves, and increased OsNHX1 expression contributes to Na+ compartmentalization in old leaves. In addition, lower expression of OsHKT1;5 and OsSOS1 in old leaves decreases frequency of retrieving Na+ from old leaf cells. Excess of Na+ weakens GOGAT/GS pathway and elevates GDH pathway in old leaves. The up-regulation of OsNRT1;2, a gene coding nitrate transporter, advances the accumulation of NO3− in the old leaves of salt stressed-rice.