The effects of NaCl and mannitol iso-osmotic stresses on calli issued from sugarcane cultivars (cvs.) R570, CP59-73 and NCo310 were investigated in relation to callus growth, water content, ion and proline concentrations. Callus growth and water content decreased under both stresses with the highest reduction under mannitol-induced osmotic stress. The ion concentration was drastically affected after exposure to NaCl and mannitol. Salt stress induced an increase in Na+ and Cl– accumulation and a decrease in K+ and Ca2+ concentrations. Under mannitol-induced osmotic stress, K+ and Ca2+ concentrations decreased significantly while Na+ and Cl– concentrations remained unchanged. Free proline accumulation occurred under both stresses and was more marked in stress-sensitive cv. than in stress-resistant one. Our results indicated that the physiological mechanisms operating at the plant cell level in response to salt- and osmotic-induced stress in sugarcane cvs. are different. Among the cvs., we concluded that the stress resistance is closely related to the maintain of an adequate water status and a high level of K+ and Ca2+ under both stresses and a low level of Na+ concentration in the presence of NaCl. Thus, sugarcane (Saccharum sp.) can be regarded as a Na+ excluder. We also provided evidence that proline accumulation is a stress-sensitive trait rather than a stress resistance marker.
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