عنوان مقاله [English]
نویسندگان [English]چکیده [English]
Introduction: Horsemint (Mentha longifolia L.) is a valuable medicinal and aromatic plant belonging to Lamiaceae family. It was reported that the contents and composition of perceived pharmacological properties varied significantly among populations. The genus Mentha L. (Lamiaceae), is widely distributed in all continents (except in South America and Antarctica). The systematic of the genus is not very elucidated because of the strong morphologic variations, levels of ploidy (2n = 2x = 24 to 2n = 6x = 96), and hybridizations intra- and interspecific (or between spontaneous and cultivated forms). M. longifolia or horsemint is a fast-growing and perennial herb which cultivated in all regions. The species possesses antimicrobial and antioxidant properties. The antimicrobial properties of the essential oils can be attributed to the presence of pulegone, menthone and neomenthone because they can destroy the structure of different polysaccharides, fatty acids and phospholipids by altering the permeability of the cell membrane and destroying the bacterial wall. The essential oils of horsemint are said to be cyclohexane and aromatic, and pulegone is the main compound of these oils has a definite aroma in the range of intense to spicy mint. The effects of environmental conditions on the plant growth and development, reproduction and distribution are well known in plant ecology. Many studies have been carried out about the relationships among plant chemical contents, biological activity and environmental variables in the natural and cultivated plant species. This information has been used to determine the medicinal value and economic importance of plant products.
Materials and Methods: In this research, the effects of six habitats with different altitudes (habitats of Amol city) on some morphological and biochemical characteristics of horsemint plants were investigated in a completely randomized design with three replications. This study was done to compare the amount of pulegone, total phenol, total flavonoids, antioxidant activity, chlorophyll a, chlorophyll b, total chlorophyll, carotenoid and also morphological features of horsemint such as number of leaves per plant, number of branches per plant, number of flowers and number of nodes. For antioxidant properties using DPPH method in 517 nm wavelength, total amount of phenol using Folin-Ciocalteu method in 765 nm wavelength and the total amount of flavonoid were done using the aluminum chloride method in 415 nm wavelength and they were measured by spectrophotometer. Essential oil was extracted from dried aerial parts using distillation by Clevenger apparatus for 3 hours. Gas chromatography (GC) was used to measure pulegone.
Results and Discussion: The results showed that the altitude and ecotype significantly affecting the growth and biochemical characteristics of horsemint plant. The highest number of leaves (25) and the shoots (27) of horsemint were obtained in the Gat Lash region with 2000 meters and Siozmin with 1850 meters above sea level, respectively. Gat Lash and Siozmin had the highest and lowest content of photosynthetic pigments, respectively. Although there was no significant difference between the content of phenol and flavonoids in different habitats, the highest rates were observed in the Pardemeh and Gat Lash habitats. The results showed that the highest and lowest oil were obtained from ecotypes of Gat Lesh with 2000 meters and Vash Verin with 2300 meters above sea level, respectively. As the height increased, the amount of pulegone was also increased in the leaves, so that the highest amount of pulegone was found in Pardemeh )6069 ppm) habitat by 2600 meters above sea level.
Conclusions: Generally, for obtaining the highest essential oil content and pulegone, the best ecotypes were Gat Lash and Pardemeh habitats, respectively. Due to the importance and usage of secondary metabolites in the human life, investigating the relationship between environmental conditions with the production and accumulation of secondary metabolites in plants can be very useful. Our results showed that the climatic conditions had a significant effect on the morphological characteristics of the horsemint, thereby increasing or decreasing the essential oil. In the present study, the best habitat for the highest pulegone was Pardemeh habitat but the habitat of Gat Lash could be a suitable habitat for domestication and cultivation of this plant because of its higher essential oil yield and relatively good pulegone content. For this purpose, it is recommended to study different habitats of this species in other parts of the country for finding the best ecotypes.