Role of L-phenylalanine in enhancing salt tolerance in carrot (Daucus carota L.) through morpho-physiological, antioxidant, and ionic modification

A b s t r a c t. Salt stress is one of the major abiotic stresses that affects the growth and development of the carrot.To evaluate its function in carrot salt tolerance, a pot experiment was conducted with three salinity levels (0, 60, and 120 mM NaCl) and three L-phenylalanine concentrations (0, 100, and 200 ppm).Salt stress significantly reduced the shoot fresh weight by 28% and the root dry weight by 50%, respectively.Under salinity (120 mM), photosynthetic pigments such as total chlorophyll content decreased by 35% and carotenoids by 28%, while H 2 O 2 and MDA increased by 35.5 and 27%.Additionally, Na⁺ accumulation increased and K⁺ and Ca²⁺ accumulation declined.The foliar application of L-phenylalanine (200 ppm) increased the shoot fresh weight by 38% and the root dry weight by 92%, total chlorophyll and carotenoids increased by 54 and 39%, respectively.Upon the foliar application of L-phenylalanine, SOD increased by 54%, CAT by 43%, and POD by 36% under salt stress.Non-enzymatic antioxidants, such as leaf ascorbic acid content increased by 32%, flavonoids by 39%, and anthocyanins by 50%.K⁺ and Ca²⁺ accumulation increased after the application of L-phenylalanine.Overall, L-phenylalanine improved morpho-physiological performance, suggesting its potential as a biostimulant for carrot production under saline conditions.K e y w o r d s: carrot (Daucus carota L.), salinity stress, L-phenylalanine, antioxidant defense, secondary metabolites, osmolytes