Seasonal Variation in Chemical Composition of Cistus albidus L. from Spain**

Abstract

The chemical composition of the oils of two samples of the same population of Cistus albidus gathered in Spain during winter and spring, have been analyzed by GC and GC/MS. All the samples were characterized by a high percentage of sesquiterpenes while monoterpenes were totally absent. Most of the differences detected in the flower oils (SF) were quantitative, although small qualitative ones were also found. The principal compounds of the winter leaf oils (WL) were identified as zingiberene (14.8%), aromadendrene (10.6%), ar-curcumene (10.6%) and guaiol (6.5%), whereas the oil from the spring leaves (SL) contained as main constituents aromadendrene (9.2%), ar-curcumene (8.8%), zingiberene (8.0%) and guaiol (7.0%). The flower oils also contained these components but the major ones were found to be α-cadinol (8.4%) and zingiberene (8.1%). The seeds of this species were the part of the plant with less yield oil. As far as we know, this is the first report about the seasonal variation on the chemical composition of the oil of this species isolated by hydrodistillation and analyzed by GC and GC/MS.

Key Word Index

Cistus albidus, Cistaceae, essential oil composition, aromadendrene, ar-curcumene, zingiberene, guaiol, α-cadinol, seasonal variation.

Introduction

The genus Cistus L. belongs to the Cistaceae family and comprises 12 species in Spain (1). This genus is widely distributed in the Mediterranean area and their species are considered pioneers in disturbed environment. They are pyrophytes, and represent the key stage in the successional dynamic because they are one of the first shrubs to emerge after fire, which increase the germination of the plant s seeds (2). Cistus albidus L. is an evergreen woody shrub up to 1.5 m in height. The leaf surface shows a very dense cover of hair that gives it a pale green, cottony character, being the only Cistus with pilous leaves. It grows on both calcareous and siliceous soils of different Mediterranean countries, and is well represented throughout Spain, although it is more common in the mid south (3).

Numerous studies have been published on Cistus species, particularly on their volatile constituents (4-12). They show the presence of a high number of compounds with antimicrobial and antifungal properties (13-18).

Physiological studies have been previously reported in this species (C. albidus). A water deficit conditions caused a reduction in the shoot, stem, leaf and root dry weights and in the total leaf area. It also responded to a water deficit by developing avoidance mechanisms based on stomatal closure, a reduction in the leaf area and root hydraulic conductivity and epinasty (19). The autotoxic and allelopathic properties of C. albidus oils have been also tested. Although the oils had little effect on germination, a significant increase in the number of non-viable seedlings and inhibition of normal seedling growth was shown. The toxic potential exhibited was higher in populations living in calcareous soils. The efficient allelopathic effect of this species could explain the low number of plant species found in C. albidus shrubberies and the lack of population renewal (20). Other physiological aspects of this species such as the allocation of absorbed energy also have been studied (21).

With respect to its chemical composition, the seasonal pattern of terpene content and emission has been studied under field conditions. This species stored a large amount of terpenes with maximum values in autumn and minimum values in spring. The most abundant terpenoid compound was β-caryophyllene. This compound, together with limomene, was the main compound emitted during the spring, although the emission of another non-terpenoid C6 compound, (Z)-S-hexenol, was also detected (22-24).

Finally, the oil of this species from France did not show qualitative differences between the compositions of the essential oils from samples growing on calcareous or siliceous soils. The oil yield of plants growing in calcareous soils was always smaller. The oils were mainly constituted by sesquiterpenes, zingiberene, δ-cadinene, β-caryophyllene, allo-aromadendrene, α-curcumene, α-bisabolol, α-cadinol and an unidentified sesquiterpene (25).

In this present work, we report on the changes of the oil composition of C. albidus from Spain gathered in different seasons of the year. As far as we know, this is the first report about the seasonal variation on the chemical composition of the oil of this species extracted by hydrodistillation and analyzed by GC and GC/MS.

Experimental

Plant material: Two samples of the aerial parts of the same population of C. albidus were gathered in Colmenar de Oreja (Madrid province, Spain) in the winter and spring of 2002. A voucher specimen for each season (MACB-82814 and MACB-82815) was lodged at the Herbarium of the Faculty of Biology, Complutense University, Madrid, Spain.

Oil isolation: The aerial parts were divided into leaves-stems, seeds and flowers, according to the season of the year. The oils were isolated from the fresh fractions by steam distillation with cohobation for 8 h according to the method recommended in the Spanish Pharmacopoeia. The oils were dried over anhydrous sodium sulfate and stored at 4°C in the dark. The different distilled samples yielded 0.1% of oil (based on dry weight).