Effects of drought stress and jasmonic acid elicitors on morphological and phytochemical characteristics of peppermint (Mentha piperita L.)

Peppermint (Mentha piperita L.) from Lamiaceae family is one of the most widely used medicinal plants. In addition to therapeutic effects, it is used as flavoring in the production of various foods and medicinal products. In addition to genotype, the quality and quantity of active ingredients in medicinal plants are influenced by environmental factors. This research was aimed to study the effects of drought stress and jasmonic acid on the quality and quantity of peppermint as a factorial experiment in a completely randomized design at University of Zanjan in 2015. The treatments consisted of three irrigation levels [50%, 75%, and 100% (control) of field capacity] as main factor and three concentrations of jasmonic acid (0, 50, and 100 mg l-1) as sub-factor. Rhizomes of plants were used for plant production. The plant samples were collected at flowering stage and after drying in the shade, the essential oil was extracted with water distillation method by Clevenger apparatus. The essential oil components were identified by GC and GC-MS. The results showed that the highest fresh and dry weight, height, total chlorophyll and relative leaf water content were obtained in control with 100 mg l-1 jasmonic acid. The highest peroxidase enzyme content was obtained at 50% field capacity drought stress with 100 mg l-1 jasmonic acid. The highest essential oil content was obtained at 75% field capacity drought stress with application of 50 mg l-1 jasmonic acid. The main essential oil components were menthol, menthon, 1,8-cineole, cyclohexanol, and methyl acetate. The highest amounts of menthol, menton, and 1,8-cineole were obtained from 100 mg l-1 jasmonic acid and the highest amount of cyclohexanol was obtained from 50 mg l-1 jasmonic acid. However, application of jasmonic acid decreased the amount of methyl acetate from 7.24% in control to 0.56% in 100 mg l-1 of JA treatment.