Elicitation of Medicinal Plants In Vivo—Is It a Realistic Tool? The Effect of Methyl Jasmonate and Salicylic Acid on Lamiaceae Species

Salicylic acid (SA) and methyl jasmonate (MeJa) are prominent phytohormones that are involved in stress reactions. Both compounds may influence the biosynthesis of secondary compounds; however, scientific experiments in vivo are rare and contradictive. This paper reports on a study on the elicitation of volatiles and total phenolics (TPC) by MeJa and SA. The subjects were four Lamiaceae species studied in open field conditions in Budapest (Hungary). According to the results, both elicitors provoked specific responses in each plant species depending on the dosage applied and the parameter studied; 2 mM of SA stimulated essential oil (EO) accumulation in marjoram and peppermint, while in hyssop 0.1 mM was optimal. MeJa proved to be effective only in marjoram and in basil. In marjoram, cis-sabinene hydrate was decreased and in hyssop, isopinocamphone was increased by both dosages of SA. In peppermint, pulegone content was reduced by 2 mM SA, but no significant change of the major components of basil EO was detected. SA was successful in increasing TPC and antioxidant activity (AC) in three of the experimental species, but not in hyssop. In marjoram, only 0.1 mM induced TPC and eventually AC, while in peppermint and basil both dosages of SA were effective. Optimalisation of the treatments is suggested in further in vivo experiments.