Enhancing plant drought tolerance through exogenous nitric oxide: a comprehensive meta-analysis.

Background: Drought stress severely impacts plant growth and agricultural productivity, necessitating strategies to enhance drought tolerance. This meta-analysis synthesizes data from 48 peer-reviewed studies to evaluate the effects of exogenous nitric oxide (NO) on plant growth, photosynthesis, antioxidant defense, and osmoregulation under drought conditions.

Results: Results show that NO significantly improves shoot length, root length, shoot dry weight, and root dry weight by 66.60%, 29.38%, 26.71%, and 16.17%. Photosynthetic rate, stomatal conductance, intercellular CO₂, Leaf relative water content, total chlorophyll, chlorophyll a and b was also improved by 17.98%, 67.95%, 12.12%, 10.20%, 19.68%, 52.26%, and 39.91%, respectively. Antioxidant enzyme activities, including superoxide dismutase, catalase, peroxidase, and ascorbate peroxidase, were significantly elevated by 13.69%, 22.60%, 16.98%, and 19.33%, respectively. Oxidative stress markers, including hydrogen peroxide, superoxide, and malondialdehyde, were reduced by 18.63%, 22.01%, and 18.22%, respectively. Osmotic regulators, including proline, soluble sugars, and soluble proteins, were significantly increased by 17.01%, 18.34%, and 30.40%. Subgroup analyses reveal that NO's effectiveness is influenced by environmental factors, plant species, and application methods.

Conclusions: This meta-analysis confirms that exogenous NO significantly improves the growth, photosynthetic efficiency, antioxidant defense, and osmotic regulation of plant under drought stress. The heterogeneity of NO's effects under different conditions highlights the importance of improving application methods, concentrations, and environmental conditions. These findings encourage focused research and application strategies to maximize the benefits of NO in enhancing crop resilience, and promoting sustainable agricultural practices.