Strigolactones mitigate drought stress in maize by improving chloroplast protection stomatal function and antioxidant defense mechanisms

Phytohormones and their derivatives are essential components of the signaling networks that regulate plant defense mechanisms against abiotic stress. A novel class of carotenoid-derived plant hormones, strigolactones (SLs), has been shown to modulate various physiochemical processes in plants under drought stress (DS). This study presents unique findings by optimizing the concentration of SLs to mitigate the detrimental effects of DS on maize seedlings. Drought stress significantly reduced plant growth attributes and leaf chlorophyll pigments due to excessive production of reactive oxygen species (ROS). The foliar application of SLs improved growth attributes, chlorophyll content, photosynthetic rate, and stomatal traits, while significantly reducing oxidative damage, as evidenced by a decrease in hydrogen peroxide (H₂O₂), superoxide (O₂⁻) and malondialdehyde (MDA) content (p ≤ 0.05). Furthermore, the DS + SL3 treatment significantly improved leaf ultrastructure and reduced oxidative damage, as evidenced by decreases in H₂O₂, O₂⁻ and MDA content by 32.49 %, 33.31 %, and 55.23 % (p ≤ 0.05) respectively. This treatment also increased the activities of antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and ascorbate peroxidase (APX) by 31.64 %, 49.61 %, 53.18 %, and 101.35 %, respectively. Strigolactones enhanced chloroplast structure, supported cell expansion, protected cell walls, and significantly improved stomatal traits, including number, length, and width. These findings suggest that the foliar application of SLs can mitigate the adverse effects of drought stress by upregulating chlorophyll pigments and activating antioxidant defense mechanisms to mitigate ROS damage.