Iodine application induces the antioxidant defense system, alleviates salt stress, reduces nitrate content, and increases the nutritional value of lettuce plants.

In light of climate change, improving plant resilience to abiotic stress is essential. Iodine application can improve plant tolerance to abiotic stress and provide humans with a nutritious diet rich in iodine and antioxidants. A field experiment was conducted on lettuce plants grown in a saline environment with four levels of foliar iodine spray (0, 3, 6, and 9mg/L potassium iodate). Lettuce plants respond to iodine in a concentration-dependent manner, with low iodine concentrations increasing their antioxidant capacity, reducing the amount of toxic compounds, improving their nutritional status, maintaining their physiological balance, and stimulating plant growth and yield. Conversely, high iodine levels disrupt physiological processes and reduce productivity. However, lettuce plants sprayed with 3mg/L iodine presented relatively high levels of antioxidant enzymes (catalase, superoxide dismutase, and ascorbate peroxidase), nonenzymatic antioxidants (vitamin C, proline, and phenols), chlorophyll, and nutrients, as well as relatively low levels of malondialdehyde, H2 O2 , and Na, resulting in increased head weight and total yield and reduced nitrate content. Thus, while low levels of iodine can increase plant resilience to adverse conditions such as salt stress, high levels can be detrimental, leading to reduced growth and yield. The higher the concentration of iodine used, the greater the inhibitory effect on plants.