Cyanobacterial elicitors as efficient plant growth promoters affect the biomass and metabolic profiles of four species of Mentha L.: A comparative study

Abstract

Medicinal and aromatic plants contain compounds with industrial and therapeutic applications; among which genus Mentha L. has special economic importance. The present investigation aimed to evaluate the ability of cyanobacterial strains as bio-elicitors on biomass production, as well as the quality and quantity of essential oils of four species of Mentha (M. spicata L., M. piperita L., M. aquatica L., and M. pulegium L.). Following the seedling growth test, two cyanobacterial strains, Wollea vaginicola ISB89 and Nostoc spongiaeforme var. tenue ISB91, were selected as potential bio-elicitors. Then, the growth of plants under 1% cyanobacterial suspensions was assessed by measuring growth factors including length and weight of plants, and leaf area after 90 days of planting. Moreover, the amount of essential oils of plants and their constituents were evaluated. According to the results, both cyanobacterial elicitors significantly increased plant biomasses and essential oils yield. There was a direct relationship between cyanobacterial auxins and biomass and essential oil of Mentha spp.; in this way, Wollea with a higher level of auxins and cations provides essential elements for plants. Therefore, plants treated with Wollea exhibited more growth and essential oil promoting features compared to Nostoc treatments. The most important terpenoids in essential oils of investigated species belong to oxygenated monoterpenes with 79–91% contents; including Piperitenone, Menthol, and Menthone. In M. piperita, the amount of Menthone, as one of the principal constituents of essential oil, increased under cyanobacterial elicitors (115–137%). For M. spicata the enhancement of Piperitenone (46–96%), and for M. pulegium, the increase of neo-Menthol (17–115%) was remarkable. Based on the results, two cyanobacteria strains are considered as a rich source of natural compounds and phytohormones which can be used to increase the yield and essential oil production of studied economically important plant species.