Exogenous Arginine Enhances Antioxidant Defense System and Regulates the Physiology of Lentil (Lens culinaris) under Salt Stress

Arginine (Arg) being one of the most important amino acids of plants involved in biosynthesis and induction of vital amino acid derivatives, enzymes, phytohormones and signaling molecules. The effect of exogenous Arg (3.0 mM) was investigated in salt (120 and 150 mM NaCl) treated lentil (Lens culinaris cv. BARI Mashur-2). Seven-day-old lentil seedlings were subjected to salt stress alone and in combination with Arg for 48 h. Salt stress highly raised the hydrogen peroxide (H₂O₂) content and increased membrane lipid peroxidation as indicated by increased malondialdehyde (MDA). Reduced ascorbate (AsA), increased glutathione disulfide (GSSG) content, decreased glutathione (GSH):GSSG together with altered activities of antioxidant enzymes caused the oxidative stress in salt affected plants. Salt stress decreased leaf relative water content (RWC) but increased proline (Pro) content. Chlorophyll (chl) a, b and total chl contents decreased under salt stress. Arginine co-treatment with salt stress decreased the oxidative stress through improving the AsA and GSH pool and activities of catalase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase. Decreased Pro level, improved RWC, chl content, growth parameters like plant height, root length and seedling dry weight in Arg supplemented salt affected plants are the indication of Arg-induced relaxation of salt stress and improved salt tolerance in lentil plants.