Involvement of ethylene in alleviation of Cd toxicity by NaCl in tobacco plants

• Treatment of a combination of Cd–NaCl alleviates the inhibition of tobacco plants by Cd stress.
• It is Na+, rather than Cl−, that alleviates Cd toxicity.
• Cd–NaCl treatments enhanced and inhibited ethylene production in roots and in leaves, respectively.
• Addition of NaCl into the solution containing Cd regulates root growth by mediating ethylene synthesis.

The possible involvement of ethylene in alleviating cadmium (Cd) toxicity by NaCl was investigated because our previous experiments showed that a low concentration of NaCl could alleviate Cd toxicity of tobacco plants. Tobacco plants exposed to the treatment of a combination of Cd–NaCl exhibited more vigorous growth than did those exposed to the treatment of Cd stress alone, as reflected by greater biomass, longer roots, taller shoots, larger SPAD values and higher photosynthetic rates. The results also indicated that it is Na+, rather than Cl−, that alleviates Cd toxicity. Cd–NaCl treatments enhanced and inhibited ethylene production in roots and in leaves, respectively, in comparison with the plants exposed to Cd alone. However, the exogenous application of ethylene did not improve root growth under Cd exposure, indicating that ethylene is not directly involved in the rooting process. It may be assumed that the addition of NaCl into the solution containing Cd regulates root growth by mediating ethylene synthesis.