The effect of sucrose application on antioxidant defense system, proline contents and growth parameters in Helianthus annuus L. and Brassica napus L. exposed to salt stress

Salt stress is becoming an increasing threat worldwide, limiting plant growth and crop productivity. Salinity, which is a global problem, disrupts the osmotic and ionic balances of plants, causing osmotic stress, ionic stress and nutrient imbalances that can ultimately result in the death of the plant. To cope with the harmful effects of salt, plants activate their ecological, physiological and molecular mechanisms that can increase their tolerance level to salt. Exogenous supplementations of various osmoprotectants such as sucrose, trehalose, glycine betaine, proline, which are applied to increase the tolerance of plants to salinity, also play an extremely effective role in improving the negative effects of salt stress on plants. In this study, the effects of salt application at two different concentrations (75 and 150 mM NaCl) and exogenous sucrose applied together with these concentrations (75 mM NaCl+Sucrose and 150 mM NaCl+Sucrose) on sunflower and canola plants were investigated. Root and stem lengths, root and stem fresh-dry weights, root and stem biomass, tolerance indices, chlorophyll amounts, lipid peroxidations, proline contents, total protein amounts, SOD, CAT, APX enzyme activities and changes in the gene expression level of antioxidants of sunflower and canola plants treated with salt and exogenous sucrose were determined. As a result, it was observed that salt stress negatively affected the growth parameters in both plants species, decreased the amounts of chlorophyll, and increased the amounts of MDA, proline and total protein depending on the increasing salt concentration. It was determined that SOD activity increased, CAT activity decreased, and APX activity did not undergo a significant change in salt-treated sunflower and canola samples compared to the control. It was noted that the P5CS, SOD-Mn and APX gene expressions of antioxidants increased, while the CAT gene expression did not change significantly. It was determined that exogenous sucrose supplementation applied to sunflower and canola plants improved the ecological parameters of the samples exposed to salt stress, increased the amounts of chlorophyll, and decreased the amounts of MDA, proline and total protein. It was observed that exogenous sucrose application decreased the SOD activity of the plants and increased the CAT and APX activities compared to the only salt applied samples. It was found out that under salt stress, sucrose differently affected the gene expressions of antioxidants in sunflower, while it increased the mRNA expression levels of antioxidants in canola. Although the tolerances of plants to salinity are not very different, it has been observed that the growth related salt tolerance in sunflower is relatively higher than that of canola. Exogenous sucrose has also been shown to increase salt tolerance more in sunflower than in canola. In line with the results obtained at the ecophysiological and molecular level, it has been determined that exogenous sucrose has an amendatory effect by alleviating the negative effects of salt stress in both sunflower and canola.