Foliar application of gallic acid improves tolerance to cadmium stress in wheat: an NMR-based metabolomics approach

Potentially toxic metals (PTM) in agricultural crop systems significantly threaten crop yield and productivity. PTM disrupts biochemical and molecular functions within plants, affecting critical processes such as nutrient uptake, photosynthetic efficiency, and the maintenance of redox balance. This study investigated the impact of cadmium (Cd) toxicity on wheat seedlings and the protective role of foliar-applied gallic acid (GA) in mitigating Cd-induced stress using an NMR-based metabolomics approach. Cd exposure significantly impaired wheat seedlings' growth (root and shoot length) and biomass accumulation (dry weight). Cd stress severely reduces the dry weight/length ratio in shoots and roots, indicating less efficient biomass accumulation and poor tissue development. Foliar application of gallic acid enhanced biomass allocation, especially at higher concentrations of Cd. Forty-one metabolites were identified via ¹H NMR metabolomics, and multivariate statistical analyses allowed the identification of key metabolic changes associated with the exposure to Cd. For example, histidine, lactate, maltose, and o-phosphocholine were found only in Cd-exposed shoots and roots, whereas exposure to Cd depleted arabinose, galactose, malate, proline, ribose, sucrose, thymine, and uracil. However, foliar application of GA nearly restored these metabolites to control levels. NMR spectroscopy enabled the comprehensive profiling of wheat metabolites under cadmium stress, revealing key metabolic shifts and linking biochemical changes to stress tolerance and plant growth. These findings highlight gallic acid potential to enhance wheat tolerance to Cd stress by improving growth and antioxidant defenses, as well as partially restoring wheat metabolic fingerprint.