Wheat seed priming in relation to salt tolerance: growth, yield and levels of free salicylic acid and polyamines

The exogenous application of cytokinins through seed pre-treatment is reported to be involved in plant tolerance to salt stress. It was hypothesized that cytokinins could regulate the salinity-induced changes in hormonal balance for adequate physiological adaptation to stressful environments in plants. Thus, the present studies aimed to assess the effects of pre-sowing seed treatment with varying levels (100, 150 and 200 mg l(-1)) of cytokinins, namely kinetin (Kin) and benzylaminopurine (BAP), on growth, yield, and leaves' endogenous levels of salicylic acid and polyamines (putrescine, spermidine and spermine) in two spring wheat (Triticum aestivum) cultivars, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant). The primed and non-primed seeds were sown in a field in which NaCl salinity of 15 dS m(-1) was developed. The experiments were conducted during the years 2002 and 2003. Of the different priming agents, Kin was very effective, particularly in improving growth and grain yield in both cultivars. Priming with mild concentration (100 mg l(-1)) of Kin in the salt intolerant and moderate concentrations (150 mg l(-1)) of BAP and Kin in the tolerant cultivar increased leaf free salicylic acid under saline conditions. BAP priming increased leaf free polyamines (Spermidine and Spermine) in both cultivars under salt stress. Plants of the salt tolerant cultivar raised from non-primed seeds accumulated more putrescine in the leaves as compared with plants raised from primed seeds. In conclusion, seed priming with moderate concentration of Kin showed a consistent beneficial effect on growth and grain yield in both cultivars under salt stress. The mechanism by which Kin-priming induced salt tolerance in wheat plants remains unclear.