Sodium transport in the seedlings of two bread wheat (Triticum aestivum L.) genotypes showing contrasting salt stress tolerance

In many plant species, salt sensitivity is associated with the accumulation of sodium (Na+) in photosynthetic tissues. Na+ uptake to leaves involves a series of transport steps and for which only few candidates' genes have been so far characterized. In this study, we provide a physiological and molecular analysis of two Algerian bread wheat varieties (Triticum aestivum L.), Mahon-Demias (MD) a salt sensitive and Hidhab (HD) a salt tolerant varieties. The comparative analysis of Na+ transport revealed two major differences between the two genotype i) a lower rate of transfer from the root to the shoot (xylem loading) in the salt tolerant genotype, and ii) A higher capacity of the leaf sheath in the tolerant genotype to extract and sequester Na+ as it entered the leaf. In addition, an enhanced uptake of K+ in leaves of Hidhab compared to Mahon-Demias resulting in a higher K+/Na+ ratio in leaf blades and hence improving cellular homeostasis in the tolerant variety. Moreover, correlation was observed between the expression patterns of the transcripts encoding the plasma membrane Na+/H+ antiporter (TaSOS1), two members of the HKT transporters family (HKT1;5 and HKT2;2) and the Na+ fluxes from roots to leaves. All together, these results help to understand the differential salt stress tolerance between Hidhab and Mahon-Demias wheat varieties. More interestingly, our data may ultimately contribute to deciphering the physiological and molecular mechanisms of salt stress tolerance in bread wheat, and hence to assist breeders in selecting salt tolerant genotypes.