Mitigation effects of non-enzymatic antioxidants in maize (Zea mays L.) plants under salinity stress

The effects of non-enzymatic antioxidative compounds such as ascorbic acid, thiamine HCl and β-carotene were investigated on salt stressed maize plants. The maize plants were sprayed with 100 mg L of ascorbic acid, thiamine or β-carotene solutions once a week, up to harvesting of plants. The treatment of NaCl was initiated 25 days after sowing by irrigating the plants with 125 mM NaCl solution. Plants for physiological and biochemical measurements were harvested at the cob formation stage and for yield 90 days after seedling emergence. The results showed that although salt stress reduced the shoot and root dry weights and macro-element contents of maize plants, exogenous application of non-enzymatic antioxidants improved the above-mentioned parameters of maize plants under saline conditions. Shoot and root dry weights increased significantly (P < 0.05) by the ascorbic acid treatments. Salt stress enhanced the activities of superoxide dismutase (SOD; EC: 1.15.1.1), peroxidase (POX; EC: 1.11.1.7) and polyphenol oxidase (PPO; EC: 1.10.3.1). Proline content also increased significantly in maize plants in response to NaCl stress. Although the SOD activity increased significantly with ascorbic acid treatment, the POX activity increased considerably with β-carotene application. Of the non-enzymatic antioxidative compounds tested, ascorbic acid was more effective than the others in protecting maize plants from salinity stress. The results of the present study indicate that foliar application of non-enzymatic antioxidative compounds alleviated the detrimental effects of salinity and increased resistance to salinity in the maize plants by improving the antioxidative defense system.