Evaluation of physiological respons of canola cultivars to salt stress at germination and seedling establishment stage

High salinity in soil or irrigation water is a common environmental problem affecting seed germination and plant growth. Salinity mainly causes hyper-osmotic stress and hyper ionic toxic effects; the consequence can be plant death .Salt and osmotic stresses are responsible for both inhibition or delayed seed germination and reduced seedling establishment. Salt stress decreases germination percentage, shoot length and root length of canola cultivars. The increasing evidences also suggest that high salinity induces oxidative stress which is a key underlying component of most abiotic stresses. Reactive oxygen species (ROS) are generated as by-products of plant cellular metabolism and are also important as signaling molecules. This study aims to investigate the effect of salt stress on seed germination, seedling growth, antioxidants enzymes activities and ion concentration of canola cultivars. The present study was conducted to investigate the influence of salinity on seedling growth, ion concentration and antioxidants enzymes activities in two separated experiment. The seeds of  canola cultivars were obtained from the oil plant research Institute, Karaj, Iran. The experiment was carried out under a two-factorial (cultivar × salinity level) Sodium chloride was used as a source of salt. Salinity levels were 30, 60 and 90 mM NaCl solution and distilled water served as the control (0 ds/m) and four canola (B. napus L.) cultivars include Hayola 330, Hayola 320, Hayola 401 and sarigol.  Ion concentration, antioxidants enzymes activates, seed germination, seedling growth, soluble carbohydrate and proline concentration were assay in this research. Salt stress decreased canola seed germination and seedling growth. At 60 mM NaCl treatment, maximum germination percentage obtained in Hayola 330 and Hayola 320 cultivars (76% and 77% respectively) and in 90 mM NaCl n, Hayola 330 had maximum germination percentage. Salt stress decreased seedling weight and in 90 Mm treatment, maximum dry weight obtained in Hayola 330 cultivars (1.72 g). Salt stress increased Na+ concentration and decreased K+ concentration in canola cultivars. Hayola 330 and Hayola 320 showed maximum K/Na ratio compared other canola cultivars in 60 mM and 90Mm NaCl treatments. Hayola 330 and Hayola 320 had higher antioxidant enemies activates, soluble carbohydrate and proline concentration compared Hayola 401 and Sarigol  , too. Our results showed that salt tolerant cultivars have higher K+ concentration and K/ Na than salt sensitive cultivars. On the other hand, this study showed composite correlation between increase of K+ and decrease of Na+ with growth of rapeseed seedling. Salt-tolerant cultivars generally show higher activity of antioxidant enzymes and K/Na as compared to salt-sensitive ones  This suggests that high antioxidant enzyme activity and ion concentration has a significant role in imparting salt tolerance in plants. Researchers suggested that K+ concentration observed in salt stress tolerant plants were more than that of susceptible cultivars led to decreased Na+ toxicity. Increased Na+ content led to decrease in seed germination level and seedling dry weight in canola cultivars. Proline and soluble carbohydrate are important osmoprotectant in plants. Under salt stress most plant species exhibit a remarkable increase in their proline and soluble carbohydrates content.  In our experiments we also observed a similar behavior in the seedling of canola. In conclusion, our data indicates that salt-induced oxidative damage occurs in canola cultivars despite concomitant increases in the activities of antioxidant enzymes. Hayola 330 and Hayola 320 were salt stress tolerant cultivars compared other cultivars because under salinity stress condition these cultivars had maximum K/Na, seedling dry weight and antioxidants enzymes activates.  In fact, Hayola 330 and Hayola 320 cultivars were most salt tolerant due to maintenance of higher germination and seedling weight under saline conditions with maximum higher antioxidant enemies activates, soluble carbohydrate and proline concentration compared Hayola 401 and Sarigol.   Our results indicated that Hayola330 and Hayola 320 cultivars had a higher capacity for the tolerant salinity in comparison with sensitive cultivars.