Changes in growth and in solute concentrations in sorghum leaves and roots during salt stress recovery

Seedlings of two sorghum genotypes [Sorghum bicolor (L.) Moench], one salt tolerant (CSF 20) and another salt sensitive (CSF 18) were exposed to 0 (control) and 100 mM NaCl (salt stress) in nutrient solution for seven days and, then, transferred to a new nutrient solution with no added NaCl for an additional period of five days (salt recovery). Plants were collected at the 7th (salt stressed) and 12th days (salt recovered) and relative growth rate (RGR) and organic and inorganic solutes in leaves and roots were determined. Salinity reduced RGR and increased Na+, Cl−, soluble carbohydrates and proline concentrations, and Na+/K+ and Na+/Ca2+ ratios, especially in the leaves of the salt sensitive genotype. During salt stress recovery, RGR of roots was lower in previously stressed seedlings, but shoot growth did not differ between these seedlings and control unstressed ones, in both genotypes. Salt recovered seedlings showed decrease in leaf Na+ plus Cl− concentrations and in Na+/Ca2+ ratio, and in root Na+/K+ ratio. The reductions in organic solutes concentrations were quite small, especially in the older leaves. A lower toxic ion accumulation during salt stress was related to salt tolerance and to seedling growth during salt recovery phase. On the contrary, higher leaf organic solute accumulation during salt stress was not related nor to salt tolerance nor to seedling recovery after salt stress relief. So, the high capacity of sorghum seedlings to recover after salt stress relief appears to be related to an adequate partition of carbon between shoots and roots and to changes in absorption, transport and re-translocation of salts.