Salvia officinalis L., commonly known as sage, is a medicinal plant rich in various pharmacologically active metabolites, particularly terpenoid compounds. It exhibits a broad spectrum of biological activities, including antioxidant, antimicrobial, anti-inflammatory, and antidiabetic effects, making it a valuable source for therapeutic applications and phytochemical research. This study explores the effects of foliar application of amino acids (phenylalanine, glutamine, and cysteine) at 200 ppm on the essential oil content and composition of Salvia officinalis. Amino acids were applied five times at 10-day intervals, with plant samples collected at the flowering stage. Essential oil was extracted using a Clevenger-type apparatus and analyzed by gas chromatography-mass spectrometry (GC-MS). The results showed that the combined application of cysteine and glutamine significantly enhanced essential oil content (1.17 w/v%), surpassing all other treatments, including the control. Glutamine alone also increased content (0.92 w/v%), while phenylalanine treatments showed moderate improvements. Cysteine-treated plants exhibited the highest concentration of 1,8-cineole (49.99%), while phenylalanine and glutamine treatments led to lower levels, indicating competition between amino acid-driven biosynthetic pathways. Limonene production was significantly increased in phenylalanine and cysteine-treated plants (12.44%), while camphor content was highest in phenylalanine and glutamine treatments (18.31%). Minor constituents such as tricyclene and p-cymene remained stable, but α-humulene and E-caryophyllene increased under specific treatments. The synergistic effects of amino acid combinations, particularly enhancing γ-terpinene and camphene concentrations, suggest that amino acids modulate terpene biosynthesis. These findings highlight the potential of amino acid treatments as biostimulants to optimize S. officinalis essential oil profiles, with applications in medicinal and industrial contexts.
