Exogenous sucrose alleviates salt stress in sunflower (Helianthus annuus L.) and canola (Brassica napus L.) by modulating osmotic adjustment and antioxidant defense system

Salinity, a major ecological problem worldwide, adversely affects plant growth and productivity. Osmoprotectants are a possible strategy for plants to cope with and regulate their response to unfavorable environmental conditions, such as salinity. However, the role of sucrose in this process requires more precise elucidation. This study aims to investigate the ameliorative role of sucrose on growth parameters, proline content, antioxidant enzyme activity, and gene expression in sunflower and canola under salt stress. The treatments included a 3% sucrose concentration and two levels of salinity (75 and 150 mM NaCl). Salinity caused a remarkable reduction in stem-root growth, chlorophyll amounts and catalase (CAT) activity, whereas it unchanged ascorbate peroxidase (APX) activity. Furthermore, both plants grown under salt stress had considerably higher total protein, proline, malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity. Exogenous sucrose increased plant growth, chlorophyll amounts and the activities of hydrogen peroxide-detoxifying antioxidant enzymes such as CAT and APX in salt-stressed plants, but dramatically depressed levels of osmoregulators such as protein and proline. Besides that, it balanced antioxidant enzyme levels by regulating SOD activity to the required level, thereby facilitating the effective operation of the antioxidant defense system. Additionally, sucrose had a different effect on gene expressions of antioxidants in sunflower and canola under salinity. These results revealed that sucrose can ameliorate the deleterious effects of salinity in sunflower and canola by modulating osmotic substance accumulation, the activity of antioxidant enzymes, and their gene expression. In conclusion, sucrose can be a potential tool for plants in salt stress alleviation.