مطالعه برخی صفات ریختشناسی، فیزیولوژیک و فعالیت آنزیمهای آنتیاکسیدانی در گیاه شیرتیغک (L. arvensis Sonchus )تحت تنش شوری.

Background and Objectives: Perennial sow-thistle (Sonchus arvensis L.) is a medicinal plant belong to the sunflower family with anti-diabetic, antidepressant and anti-cancer properties. The crisis of salinization of agricultural lands is considered as one of the most important problems of the world and Iran, and as an environmental stress, it has a direct effect on many plant characteristics under stress. Since there is little information about the response of Sonchus plant to salinity stress, the present experiment was conducted to investigate the effect of salinity on some morphological and physiological traits as well as the activity of antioxidant enzymes under salinity conditions. Materials and Methods: The experiment was conducted as a completely randomized design with three repetitions in 2018 in the greenhouse of the Faculty of Agriculture of Urmia University. Salinity stress was applied at four levels (0, 50, 100 and 150 mM of NaCl salt) at the 6-8 leaf stage, and shoot dry weight, root dry weight and root length were recorded. Also, photosynthetic pigments (chlorophyll a, chlorophyll b and carotenoids), protein content, relative leaf water content (RWC), proline and carbohydrate contents, antioxidant capacity (DPPH and FRAP) and the activity of antioxidant enzymes including catalase (CAT), ascorbate peroxidase (APX), superoxide dismutase (SOD), peroxidase (PX) were measured in the lower and middle leaves of the plants. Analysis of variance (ANOVA) for the obtained data and comparison of the means of the treatments using Duncan’s test were implemented in SAS 9.4 software. Results: The results showed that root length, root dry weight and shoot dry weight decrease significantly with increasing salinity level. Also, the content of chlorophyll a and b increased in salinity conditions, while salinity decreased the amounts of carotenoids. The highest amount of chlorophyll was observed in the lower leaf under 150 mM NaCl. The content of protein, proline and soluble sugar was enhanced with increasing salinity level; the maximum amount of these parameters was observed in the middle leaf at 150 mM NaCl. The highest amount of total phenolic and flavonoid compounds was observed at the stress level of 50 mM NaCl. The content of sodium ion (Na+) increased with increasing salinity level, while the amount of potassium ion (K+) declined. The activity of superoxide dismutase, catalase, peroxidase and ascorbate peroxidase enzymes, as well as FRAP and DPPH antioxidant capacity increased in salinity conditions. Conclusion: According to the obtained results, it can be concluded that Sonchus arvensis plant copes with salinity through increasing some osmolytes under stress conditions. Moreover, an enhancement of the amount of chlorophyll a and b at high levels of salinity showed that Sonchus arvensis is probably a salt-tolerant plant. [ABSTRACT FROM AUTHOR]