Improvement of Growth and Stimulation of Biosynthesis Pathway of Polyphenols in Melissa officinalis L. Colonized by Arbuscular Mycorrhizal

The increasing demand for medicinal plants has amplified the importance of the development of effective methods for enhancing the cultivation of these plants. The association of arbuscular mycorrhizal (AM) fungi with medicinal plants has been found to alter the level of secondary metabolites by affecting the plant metabolism. Lemon balm (Melissa officinalis L.), is an important medicinal plant belongs to Lamiaceae family that has been used since the Middle Ages for various medical purposes. In this study, the effects of Glomus mosseae and Glomus intraradices symbiosis on growth, the content of some phenolic compounds and the activities of some enzymes responsible for polyphenols synthesis were investigated in lemon balm. Seeds were sown in a mixture of soil and fungal inoculum. After five months of growth under controlled condition, growth parameters, the contents of total phenols, flavonoids, phenolic acids and anthocyanins, the concentrations of rosmarinic acid, salvianolic acid B and caffeic acid and activities of phenylalanine ammonia lyase and tyrosine aminotransferase were investigated in control and AM plants. According to the results, the symbiosis of lemon balm with selective AM species was successful. The highest percentage of colonization and the improvement of growth parameters were observed in the plants inoculated with G. mosseae. Symbiotic plants showed more increased levels of polyphenols and enzymes activities than control plants. The study revealed that colonization of plants with AM species not only improved growth, but also increased the content of polyphenols which is closely linked to the enzymes activities responsible for synthesis of these compounds. These results confirmed the importance of the mycorrhizal symbiosis in enhancing the nutritional and medicinal values of the plant.