Effect of seed priming with salicylic acid and ascorbic acid on antioxidant activity, grain yield and oil content of sunflower (Helianthus annuus L.) under normal and water deficit conditions

Introduction Sunflower is one of the major and most important non-conventional oilseed crops in the world due to its excellent oil quality. Though sunflower is known as a drought tolerant crop or grown under dry land conditions, substantial yield increases are obtained with frequent irrigation. Drought stress damages the thylakoid membrane, disturb its functions, and ultimately decrease Photosynthesis and crop. Drought stress usually induces the accumulation of reactive oxygen species (ROS), which cause oxidative damage to plants. If not effectively and rapidly removed from plants, ROS can damage a wide range of cellular macromolecules such as lipids, enzymes and DNA. Plants can protect themselves against oxidative damage by antioxidant system including antioxidative enzymes and nonenzymatic compounds. Materials and Methods This study was done in agricultural research farm of the Islamic Azad University, mahabad Branch in south of West Azerbaijan, Iran during 2014 to 2016. The experiment was laid out in a split plot on the basis of randomized complete block design with three replications. The main plots included two irrigation regimes (Irrigation after 50 mm evaporation from class A pan and irrigation after 100 mm evaporation from class A pan, as control and water stress conditions, respectively) and the sub plots included three seed praiming with salicylic acid (0 (control), 100 and 200ppm) and seed praiming with ascorbic acid (0 (control), 50 and 100ppm). Common Sunflower seeds (cv. Euroflore) were soaked for 6 h in salicylic acid and ascorbic acid solutions. In this research superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), Di-tyrosine (D.T), Malondialdehyde (MDA), grain yield and oil perecentage was measured.Finally all data were analyzed by SAS. 9.2 statistical software and the means were compared by Duncan′s Multiple Range Test at the 5% probability level by MSTAT-C. Result and discussion Analysis of variance showed, there was significant difference between irrigation levels in terms of effect on all traits. Effect of salicylic acid and salicylic acid and ascorbic acid interaction on all traits was significant except of malondialdehyde. The effect of ascorbic acid and salicylic acid whit irrigation levels interaction on all traits except of amount of D-tyrosine was significant. Finally interaction of irrigation levels and ascorbic acid on the proline, catalase and malondialdehyde were significant. In this study water deficit increased amount of proline, catalase, superoxide dismutase, glutathione peroxidase, D-tyrosine and Malondialdehyde by 9.75, 19.18, 36.83, 14.36,17.51 23.97 and 25.10 percent, and decreased amount of grain yield and oil percentage by 51.26 and 24.48% compared with control treatment. Also priming with salicylic acid and ascorbic acid, individually or combined together increased amount of proline, catalase and glutathione peroxidase and D-tyrosine, and decreased amount of malondialdehyde compared with control treatment. Furthermore the highest grain yield (2.72 t/ha) and oil content (52.09) were belonged 200ppm of salicylic acid with 100 ppm of ascorbic acid, Also, level of 200ppm of salicylic acid and 100ppm of ascorbic acid increased the activity of proline, catalase, superoxide dismutase and glutathione peroxidase and D-tyrosine enzymes, grain yield and oil percent by 9.21, 50.35, 54.25, 49.18,48.24, 36.68 and 39.31percent compared to control treatment, respectively. Conclusions The present study indicated that drought stress increased oxidative damage, membrane lipid peroxidation and MDA content as well as antioxidant enzymes (SOD, CAT and GPX) activities, proline level and oil percentage but decresed grain yield in sunflower, nevertheless seeds priming with salsilic (especially 200 ppm) and ascorbic acid (especially 100 ppm) induced protection against drought stress via maintenance of membrane integrity by decline in MDA content and more increase in antioxidant enzymes activities (especially SOD) as well as prolin accumulation, grain yield and and oil percentage. Our results showed priming with salicylic acid and ascorbic acid it can induce drought tolerance in sunflower and improve grain yield and oil content in underwater stress conditions.