Physiological responses of bread and durum wheat seeds to osmotic stress and salinity in the early germination stage

Determining the mechanisms underlying tolerance to osmotic stress and salinity during the germination period is an essential task in order to improve agricultural production in arid and semi-arid areas. In this work, the seeds of bread and durum wheat cultivars were treated with different concentrations of polyethylene glycol (PEG)-6000 and NaCl for 1 week, and half-maximal inhibitory concentrations (IC50) of germination were calculated. The seeds were then exposed to IC50 values of NaCl and PEG-6000 for 2 days in order to assess their physiological and biochemical properties. Alpha and beta amylase enzyme activities, the reducing sugar, total sugar, proline, protein, and H2O2 contents, and DPPH radical scavenging activity of the seeds were determined by spectrophotometric methods. The results showed that the bread wheat seeds had a much higher tolerance to excess salt and osmotic stress than the durum wheat seeds. In particular, the average IC50 value of NaCl for the bread wheat cultivars was almost twice that for the durum wheat cultivars. The imbibition test revealed that the water uptake capacity of the seeds did not explain the difference in tolerance to these stress conditions. On the other hand, the bread wheat seeds exhibited constitutively higher proline, total sugar, and H2O2 contents as well as antioxidant capacity compared to the durum wheat seeds (p < 0.05). In conclusion, the current findings suggest that the interplay of oxidative metabolism and compatible solutes may contribute to improving germination tolerance under water deficit and salinity conditions in wheat.