Evaluation of the physiological and biochemical responses of wheat to NaCl stress in the seedling stage

Introduction Salinity affects about 1.7 million hectares of agricultural land in Iran, which poses a serious challenge for wheat production, as the most strategic crop in the country. Therefore, identifying wheat genotypes with salinity tolerance and selecting effective traits for accelerating the breeding process are crucial objectives. Materials and methods The experiment was aimed at assessing the response of 12 wheat cultivars to different levels of salinity using NaCl concentration as salt stress at early seedling stage under hydroponic conditions. A factorial experiment based on randomized complete block design with three replications was conducted at the research greenhouse of the Agriculture Faculty, University of Zabul, during the 2020 cropping seasons. 12 wheat cultivars (Shiraz, Falat, Durum, Gascogne, Mahdavi, Alvand, Cross Azadi, Roshan, Star, Tous, Hirmand and Cross Bolani) were irrigated with four concentrations of NaCl (0, 100, 200 and mM). The physiological and biochemical traits of wheat cultivars, including seedling fresh mass, ascorbate peroxidase, glutathione peroxidase, catalase, proline, sodium, potassium, and potassium to sodium ratio (K+/Na+) were recorded at four weeks after seed germination. Results and discussion The results showed that the amount of ascorbate peroxidase, glutathione peroxidase, catalase, proline and sodium in the leaves of wheat seedlings were increased with an increase in salinity level. In contrast, the seedling fresh mass, potassium content and K+/Na+ were decreased with an increase in salinity level. The increase of ascorbate peroxidase, glutathione peroxidase, and catalase activities, representing the main enzymatic H2O2 scavenging mechanism in wheat cultivars. In NaCl treated seedlings, Falat, Mahdavi and Cross Bolani cultivars showed higher ascorbate peroxidase than other cultivars tested. In contrast, high level of catalase was recorded in Alvand cultivar.  In the other hand, maintain the high level of proline and potassium to sodium ratio are the main mechanisms for tolerance to salinity in Shiraz and Roshan cultivars, respectively. Wheat cultivars showed different response to the increase in salinity level, while in Roshan, Mahdavi, Hirmand and Cross-Bolani cultivars, the increase in salinity level had less effect on the seedling fresh mass than other cultivars, but different patterns of changes in physiological and biochemical traits were observed in these cultivars. Salinity resistance in Mahdavi cultivar was directly related to the increase of ascorbate peroxidase and catalase, but on the other hand, in Roshan cultivar, salinity resistance was related to maintaining a high level of potassium to sodium ratio. Potassium uptake is vital for plant growth but in saline soils because of their shared transport system and physicochemical similarities, the sodium in the soil solution competes for uptake with potassium and can lead to potassium deficiency. The induced potassium deficiency inhibits growth because it plays a critical role in maintaining cell turgor, membrane potentials, and enzyme activities. In salt-tolerant cultivars of wheat such as Roshan, under salt-stress conditions, limiting sodium uptake and preventing potassium losses from the cell may help to maintain a potassium to sodium ratio in the cytoplasm that is ideal for plant metabolism. Accumulation of high amounts of proline is often related with the salt tolerance nature of crop cultivar and high proline accumulation in the salt–tolerant cultivar than in their salt–sensitive are reported previously. The regression coefficients indicated that seedling fresh weight (R2=0.89), potassium (R2=0.86) and the ratio of potassium to sodium (R2=0.69) were the most reliable predictors of the effects of increasing sodium chloride concentration. These variables accounted for a large proportion of the variance in the response variable and had significant p-values. Conclusion According to the results of this experiment, it can be concluded that seedling fresh weight, potassium, and the ratio of potassium to sodium are more suitable criteria for selecting among cultivars under salt stress conditions.