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The wheat dehydrin DHN-5 represents one of the members of the LEA (Late Embryogenesis Abundant) group 2 family. It has been previously shown to play a fundamental role in plant response and adaptation to abiotic stresses. It has also exhibited heat-protecting effect on enzymatic activities. In the present work, we report a number of findings resulting from experimentation and prediction to understand the molecular mechanism underlying the multifunction that may be attributed or directed by the DHN-5 protein. Our analysis showed that DHN-5 was not fixed on the chromatographic affinity resin (Concanavalin A) and did not react with periodic acid used for the staining of glycosylated proteins. These facts reinforced with prediction tools proved that DHN-5 is not glycosylated. In another hand, DHN-5 showed a shift on SDSPAGE electrophoretic mobility. Eventually, the proposed 3D model of the DHN-5 reinforces their disordered structure. Fold Index and Gold Plot enhance the fact that DHN-5 is an unfolded protein. On the other hand, DHN-5 possesses the ability to chelate ions, like Na+ (86 %), K+ (64 %), Mg2+ (74 %), Cu2+ (77 %), Co2+ (86 %) and Fe2+ (90 %) and could explain the tolerance of transgenic forms of Arabidopsis thaliana plants, containing the DHN-5 gene, against salinity.
Salinity is one of the severest environmental stresses affecting plant productivity. In many plant species, salt sensitivity is associated with the accumulation of sodium (Na⁺) in photosynthetic tissues. Here, we provide the physiological and molecular analyses of seedlings of two Tunisian durum wheat genotypes (Triticum turgidum L. subsp. Durum [Desf.]), Mahmoudi (salt sensitive) and Om Rabia3 (salt tolerant). Na⁺ and K⁺ contents in leaf sheath from Om Rabia3 were significantly higher than those of Mahmoudi. However, the net uptake of Na⁺ from the soil occurred at similar rates in both varieties, suggesting that Om Rabia3 has much stronger ability to limit Na⁺ flux from roots to leaf blades. This mechanism could be explained by a capacity of Om Rabia3 to retain higher Na⁺ concentration in leaf sheath and unload less Na⁺ from the xylem to the upper shoots. When treated with 100 mM NaCl leaf sheaths of Om Rabia3 developed lower water potentials and a higher relative water contents than those of Mahmoudi. These features may arise from enhanced osmotic adjustment in Om Rabia3. Measurements of stomatal conductance, free proline and chlorophyll content also indicate that Om Rabia3 is better adapted to tolerate high salt than Mahmoudi. A correlation was obtained between the expression pattern of TaSOS1 (a plasma membrane Na⁺/H⁺ antiporter) in the roots and sheaths of both wheat varieties and the Na⁺ fluxes from roots to leaves. TaSOS1 transcript accumulated in Mahmoudi than in Om Rabia3, suggesting repression of TaSOS1 in the tolerant variety that reduces loading of Na⁺ to the upper shoots. These results help to design new genetic screens for salt tolerance in wheat.
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