Exogenous Cytokinin and Salicylic Acid Improve Amino Acid Content and Composition of Faba Bean Seeds Under Salt Stress

Changes in protein content and amino acid composition of faba bean (Vicia Faba L.) seeds in response to foliar spray of 6‑benzylaminopurine (BAP: 50 μM) and salicylic acid (SA: 1 mM) were investigated under different salinity levels (0, 4, 7, and 10 dS/m NaCl as control, low, moderate and high salinities, respectively). Application of these plant growth regulators (PGR), particularly BAP + SA diminished Na⁺ content of roots and leaves, while enhanced their K⁺ content and shoot growth. SA and BAP treatments were caused the highest and the lowest root growth and root/shoot ratio, respectively. Seed number and weight per plant were improved by foliar treatments, especially by BAP + SA. Isoleucine, leucine, lysine, threonine, alanine, aspartic acid, glutamic acid, serine and tyrosine contents of seeds were increased, but valine content was decreased with increasing salinity. SA and BAP + SA enhanced isoleucine, leucine, lysine, valine as essential amino acids, and alanine, aspartic acid, glutamic acid, serine and tyrosine as non-essential amino acids. SA also increased phenylalanine under high salinity. However, treatment with plant growth regulators reduced threonine, methionine, glycine and proline contents. These results suggest that exogenous SA can generally improve protein quantity and quality in faba bean seeds.