Exogenously Applied Gibberellic Acid Enhances Growth and Salinity Stress Tolerance of Maize through Modulating the Morpho-Physiological, Biochemical and Molecular Attributes

Soil salinity is the major limiting factor restricting plant growth and development. Little is known about the comparative and combined effects of gibberellic acid (GA(3)) seed priming and foliar application on maize under salt stress. The current study determined the impact of different application methods of GA(3) on morpho-physiological, biochemical and molecular responses of maize seedlings under three salinity stress treatments (no salinity, moderate salinity-6 dS m(-1), and severe salinity-12 dS m(-1)). The GA(3) treatments consisted of control, hydro-priming (HP), water foliar spray (WFS), HP + WFS, seed priming with GA(3) (GA(3)P, 100 mg L-1), foliar spray with GA(3) (GA(3)FS, 100ppm) and GA(3)P + GA(3)FS. Salt stress particularly at 12 dS m(-1) reduced the length of shoots and roots, fresh and dry weights, chlorophyll, and carotenoid contents, K+ ion accumulation and activities of antioxidant enzymes, while enhanced the oxidative damage and accumulation of the Na+ ion in maize plants. Nevertheless, the application of GA(3) improved maize growth, reduced oxidative stress, and increased the antioxidant enzymes activities, antioxidant genes expression, and K+ ion concentration under salt stress. Compared with control, the GA(3)P + GA(3)FS recorded the highest increase in roots and shoots length (19-37%), roots fresh and dry weights (31-43%), shoots fresh and dry weights (31-47%), chlorophyll content (21-70%), antioxidant enzymes activities (73.03-150.74%), total soluble protein (13.05%), K+ concentration (13-23%) and antioxidants genes expression levels under different salinity levels. This treatment also reduced the H2O2 content, and Na+ ion concentration. These results indicated that GA(3)P + GA(3)FS could be used as an effective tool for improving the maize growth and development, and reducing the oxidative stress in salt-contaminated soils.