Proline accumulation as a response to salt stress in 30 wheat (Triticum aestivum L.) cultivars differing in salt tolerance

The effects of NaCl salt (EC = 16 dS m(-1)) on water potential, and accumulation of proline, Na+ and K+ in leaves on the main stem of 30 wheat cultivars (Triticum aestivum L.) at awn appearance and 20 days after anthesis (20 DAA) were evaluated in a greenhouse experiment. Plants were arranged in a according to a randomized complete block design with factorial treatments in three replications. Proline accumulation at 20 DAA increased with increasing salt stress. This increase was 27.4-fold with the salt-sensitive cultivar "Ghods," while the mean was 5.2-fold for 19 salt-resistant cultivars. Positive correlations between proline, and K+ + Na+ concentrations associated with higher sensitivity to salt stress indicated that proline may not have a protecting role against salt stress. No correlation was observed between leaf proline and water potential. Almost no contribution to the osmotic adjustment seems to be made by proline. The contribution made by proline to the osmotic adjustment of plants at 20 DAA was 0.69 bar, whereas that made by K+ and Na+ was 2.11 and 4.48 bar, respectively. The 30 wheat CVs used in this experiment showed different performances regarding the traits observed. Eleven of them showing the higher stress sensitivity indices had the highest level of proline and Na+ concentrations. They were considered to be salt-sensitive cultivars. Among the others, nine cultivars showed salt tolerance with almost the same Na+ and proline concentrations, but a higher K+/Na+ selectivity of ions from leaf to grains. In 10 of the cultivars, Na+ and proline concentrations were low, indicating the presence of a salt avoiding mechanism.