Clinal Variation of Mentha pulegium Essential Oils Along the Climatic Gradient of Greece

Journal of Essential Oil Research: JEOR, Nov/Dec 2004 by Kokkini, Stella, Hanlidou, Effie, Karousou, Regina, Lanaras, Tom

Abstract

The essential oil content and the C-3 oxygenated p-menthane compounds of Menthe pulegium collected from 38 populations scattered all over Greece are presented. The oil content ranged from 1.0-3.8 mL/100 g (d.w.) and the C-3 oxygenated p-menthane compounds constitute in all populations the hulk of the oil (78.6-99.7% of the total oil). The quantitative composition of the different oils varied greatly with most variable compounds being pulegone (ranging from

Key Word Index

Metha pulegium, Lamiaceae, pennyroyal, essential oil variation, p-menthane.

Introduction

The essential oils of M. pulegium L., known as European, or Old World, pennyroyal, are generally considered to be always rich in pulegone, a toxic compound (1,2). However, literature suggests that it is a chemical polymoiph species, both in the qualitative and/or quantitative oil composition (3,4). The results of our recent study (5) of M. pulegium oils obtained from 10 populations growing wild in Greece, have shown that the pulegone content varied greatly, ranging from

Experimental

Plant material: Mentha pulegium plants were collected during mid-summer from 38 populations scattered all over Greece (Figure 1): 1) Xanthi, shore of Lagoon Vistonida; 2) Kavala, Mt. Pangeon; 3) Florina, northern shores of the Lake Petron; 4) Florina, southern shores of Lake Petron; 5) Florina, near the village Nimfeo; 6) Florina, near the village Pisoderi; 7) Kastoria, eastern shores of Lake Kastoria; 8) Pclla, Mt. Vermion; 9) Ioannina, Mt. Mitsikeli; 10) Trikala, near the village Amarantos; 11) Trikala, near the village Mouria; 12) Island of Samothraki, near the village Paleopolis; 13) ibid., nearChora; 14) Chalkidiki, near the village Posidi; 15) Island of Evia, Mt. Dhirfis; 16) ibid., near the village Kremastos; 17) Korinthos, near the town Korinthos; 18) Argolida, near the village Iria; 19) Ilia, Mt. Minthi; 20) Lakonia, near the mouth of the Evrotas River; 21) Island of Lesvos, near the Monastery of Limon; 22) Island of Amorgos, near the village Egiali; 23) ibid., near Chora; 24) Island of Kos, near the village Kefalos; 25) ibid., near the town Kos; 26) Island of Karpathos, near the village Lastos; 27) Island of Crete, near the village Zaros; 28) ibid., near the village Vo riza; 29) ibid., shore of Lake Kournas; 30) ibid., near the village Katochori; 31) ibid., near the village Therissos; 32) ibid., near the village Skines; 33) ibid., between the villages Chliaro and Nea Roumata; 34) ibid., between the villages Potamida and Topolia; 35) Island of Zakinthos, near the village Vassilika; 36) ibid., near the village Kalarati; 37) Island of Kefalonia, near the village Sami; 38) Island of Paxi, near the village Paxi.

Above ground parts of 30 full-flowering individuals representing the local population were collected from each locality. Voucher specimens are kept in the Herbarium of the Laboratory of Systematic Botany and Phytogeography, Aristotle University of Thessaloniki (TAU).

Isolation of the essential oil: The collected plants were air-dried at room temperature for 10 days. Then the total plant material from each population was grossly pulverized and subjected to hydrodistillation for 2 h, using a Clevenger-type apparatus. The oil content is expressed in mL/100 g (d.w.).

oil analysis: GC and GC/MS analyses were carried out according to a previously described procedure (5).

Statistical analysis: Discriminant analysis applied, used the following variables: participation in the total oil of piperitenone piperitone (variable I), CK- trans-isopulegone pulegone (variable II), menthone neomenthol (variable Ill), isomenthone isomenthol neoisomenthol neoisomenthyl acetate (variable IV), as well as the essential oil content (variable V).

Results and Discussion

The mean essential oil content of the wild populations of each climatic zone ranged from 1.0% (zone A) up to 3.8% (zone C) (Figure 1). The lowest value (1.0%) was encountered in populations 4 and 32, while the highest (3.8%) in population 26.

Thirteen C-3 oxygenated p-menthane components were identified in total in the oils analyzed (Figure 2). Their sum, ranging from 78.6 to 99.7%, constituted the bulk of the oil. Four ketones, piperitenone, pulegone, menthone and isomenthone were detected in all oils examined. Menthofuran, the less frequent compound, was found in only nine populations, followed by neoisomenthyl acetate, detected in only 11 populations. Besides the qualitative differences between M. pulegium populations, a high variation in the proportions of the oil compounds was observed. The main components were pulegone (ranging from

In order to find out if the overall variation follows a specific pattern, a discriminant analysis was carried out, using as a priori defined groups the geographic-climatic zone wherefrom the plant material was collected. The analysis was based on a character set corresponding to the chemical profile of the samples viz. the oil content and the participation in the total oil of the following sums of compounds, representing the four major biosynthetic routes of the C-3 p-menthane pathway (Figure 3): I. piperitenone piperitone, II. cis- irans-isopulegone pulegone, III. menthone neomenthol and IY isomenthone isomenthol neoisomenthol neoisomenthyl acetate.