Ascorbic and salicylic acid regulate antioxidant defense and drought stress responses in maize

Climate change led to water scarcity becoming the greatest threat to the growth and yield of maize. Despite the application of growth promoters, the synergistic effects of ascorbic and salicylic acid application remain unexplored, regarding the biochemical mechanisms in the maize plant under drought stress conditions. This study aimed to investigate the impact of foliar applications of ascorbic and salicylic acid on inducing drought stress tolerance in maize. The treatments were comprised of drought (WW = well-watered at 85% FC, DS = drought stress at 40% FC), foliar application (NH = no-spray, DWS = distilled water spray, AA2 = ascorbic acid (200 mg/L), SA2 = salicylic acid (200 mg/L), and AA + SA = combined application (100 mg/L + 100 mg/L). Results showed that drought stress decreased morphological attributes such as shoot length (16%) and leaf area index (11%), photosynthetic pigments like total chlorophyll (15%), and carotenoid levels (19%). However, the combined foliar application of AA + SA significantly increased the above-mentioned morphological attributes (44% and 37%) and photosynthetic pigments (47% and 43%) among the other treatments. Drought stress increased the overproduction of stress indicators such as malondialdehyde (MDA) by 26% and hydrogen peroxide (H₂O₂) by 23%. However, AA + SA application reduced the overproduction of these stress indicators by 36% and 32%, through improving the activity of enzymatic antioxidants (superoxide dismutase by 45% and catalase by 38%) and the accumulation of osmolytes (proline by 46% and total soluble proteins by 20%). Overall, foliar treatment with AA2 and SA2 is a long-term approach for improving maize defense mechanisms, resulting in increased plant health and production under drought-stress environments.