Nitro-fatty acid signaling and intracellular biodistribution in plants

Nitrated fatty acids (NO₂-FAs) are biologically active molecules formed by the reaction between unsaturated fatty acids and reactive species derived from nitric oxide (NO). They are characterised by their ability to release NO, their incorporation into complex lipids and their reactivity with nucleophiles such as cysteine and histidine, facilitating post-translational modifications by nitroalkylation. The main NO₂-FAs identified in plants are nitro-oleic acid (NO₂-OA), nitro-linoleic acid (NO₂-LA), nitro-conjugated linoleic acid (NO₂-cLA) and nitro-linolenic acid (NO₂-Ln), whose concentration decreases during plant development and increases under abiotic stress. They are usually esterified with triglycerides and phytosterols in seeds and with phospholipids during vegetative growth. Although its bioactivity is still under investigation, NO₂-Ln has been shown to induce genes associated with heat shock and stress response. In addition, NO released by NO₂-FAs regulates the metabolism of S-nitrosothiols and promotes germination by degrading ABI5, a key repressor, and activating seed metabolism. NO₂-FAs-mediated nitroalkylation also plays a central role in oxidative stress response. This modification reversibly affects antioxidant enzymes such as ascorbate peroxidase (APX2) and catalase (CAT2), inhibiting their activity via adducts at catalytic residues. However, under high levels of reactive oxygen species (ROS), the adducts are oxidised, releasing NO₂-FA and restoring enzyme activity. This redox-dependent mechanism makes nitroalkylation a dynamic and adaptive regulator of antioxidant enzymes.