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Foliar Sesquiterpene Variations in Natural Populations of Cupressus dupreziana in Tassili N`Ajjer (Algeria)



M. Ramdani and T. Lograda
 
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ABSTRACT

Cupressus dupreziana A. Camus (Cupressaceae) is an endemic species in the Tassili n`Ajjer (Algerian Central Sahara). Terpenoid analysis were carried out on 160 trees of 12 natural populations with a view to determining the intra-specific variability. Eighteen sesquiterpenes were detected, including germacrene-D, which was found to be particularly abundant. The terpenoid markers used made it possible to determine the individual patterns of chemotypic variability. The variability of the sesquiterpene composition confirms that genetic factors were not responsible for the decrease in the numbers of this species. The main reason for this decrease is probably the desertification of the Tassili n`Ajjer.

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  How to cite this article:

M. Ramdani and T. Lograda, 2009. Foliar Sesquiterpene Variations in Natural Populations of Cupressus dupreziana in Tassili N`Ajjer (Algeria). Asian Journal of Plant Sciences, 8: 59-63.

DOI: 10.3923/ajps.2009.59.63

URL: https://scialert.net/abstract/?doi=ajps.2009.59.63
 

INTRODUCTION

Cupressus dupreziana is an endemic species growing on the Tassili n`Ajjers plateau. Although the plateau is hyper arid, the sub arid microclimates pertaining in some places have enabled relics of Mediterranean flora to survive. Mean annual rainfall is 30 mm and mean annual temperature 20.3°C at an altitude of 1100 m (Benhouhou et al., 2005). The plateau tends to be highly exposed and arid, although there are some patches with high humidity levels (gueltas).

Several aspects of Cupressus have been studied from the phytochemical and genetic points of view (Holeman et al., 1990; Cool et al., 1998; Cowan et al., 2001; Rushforth et al., 2003; Chéraif et al., 2007). Particular attention has been paid to sesquiterpene (Kim et al., 1994; Rafii et al., 1992; Cool, 2005; Piovetti and Diara, 1977; Piovetti et al., 1980, 1981; Pichot et al., 2008). Very little information is available so far, however, about the natural populations of Cupressus dupreziana growing in this region. Most studies on Tassili cypress have dealt with specimens of trees planted in botanical gardens. Biochemical studies have deals only with the isolation and identification of terpenoid composites and lipid components (Piovetti et al., 1981, 1982; Pauly et al., 1983). Studies on the essential oils have shown the presence of 13 sesquiterpenoids, most of which are thought by the reserachers to be artefacts (Piovetti and Diara, 1977). A critical review of the botanical studies has been published by Barry et al. (1970) and several genetic studies on the species are currently conducted by El-Maataoui et al. (1998), Pichot et al. (1998), Pichot and El-Maataoui (2000), Pichot et al. (2000, 2001) and Ramdani et al. (2007).

The terpene composition gives some important information about the variability of the population`s in-situ. Terpene variability is determined by genetic as well as ecological factors (Hanover, 1966; Squillace, 1976; Loveless and Hamrick, 1984; Yazdani et al., 1985; Baradat and Yazdani, 1988).

The availability of better GC techniques and multivariate statistical procedures led us to re-examine the foliage terpenoid contents of native stands from Tassili n`Ajjer, as well as to attempt to obtain a better picture of their chemistry and genetic relationships.

MATERIALS AND METHODS

Plant material: The plants were authenticated by the staff of the Laboratory of Natural Resource Valorization by comparison with herbarium specimens. Voucher specimens are deposited in the herbarium of the Biology Institute of the University of Ferhat Abbas, Algeria.

The present study is based on the analysis of a random sample of green branchlets of 160 trees from populations from twelve sites in Tassili n`Ajjer, as show in Fig. 1.

The site characteristics of the C. dupreziana sampled are given in Table 1. The green branchlets of natural populations of C. dupreziana and from a planted stand in Djanet were collected in April 2005. The air dried materials were subjected to hydrodistillation for 3 h using a Clevenger-type apparatus.

Table 1: Description of Cupressus dupreziana populations sampled
Image for - Foliar Sesquiterpene Variations in Natural Populations of Cupressus 
        dupreziana in Tassili N`Ajjer (Algeria)

Image for - Foliar Sesquiterpene Variations in Natural Populations of Cupressus 
        dupreziana in Tassili N`Ajjer (Algeria)
Fig. 1: Distribution of Cupressus dupreziana and sampling sites in Tassili n`Ajjer (central Sahara of Algeria)

G-C analysis: The oils were analyzed by GC on a Hewlett-Packard 5890 GC series II, equipped with FID, fitted with a SE-54 capillary column (25 mx0.25 mm; 0.25 μm film thickness). The method of analysis is largely explained by Ramdani et al. (2007).

Statistical analysis: The following sesquiterpenes were obtained in sufficiently large quantities to be able to perform statistical analysis (Baradat and Yazdani, 1988): germacrene-D, γ-cadinene, β-caryophyllene, α-humulene, γ-muurolene, δ-cadinene, 4-α-hydroxy germacrene, cedrol, δ-cadinol, β-bourberene and α-muurolene. Data were first subjected to Principal Components Analysis (PCA) to examine the relationships among the sesquiterpene components and identify the possible structure within and among populations. Cluster analysis (UPGMA) was carried out on the original variables and on the Manhattan distance matrix to seek for hierarchical associations among the populations. Statistical analysis were carried out using STATISTICA 7 software.

RESULTS AND DISCUSSION

Despite the limited resources available and the difficulty of sampling the widely scattered populations of Cupressus dupreziana in Tassili n`Ajjers, this preliminary study included 12 natural populations of each of the most accessible individuals and a planted stand growing in the Djanet gardens. The identified sesquiterpenoids accounted for 85% on average of the total sesquiterpenoid weight analysed.

They are common compounds, such as germacrene-D (68.4%), γ-cadinene (5.0%), β-caryophyllene (4.3%), α-humulene (3.5%), γ-muurolene (3.3%), δ-cadinene (3.1%), 4-α-hydroxy germacrene (2.3%), cedrol (2.1), δ-cadinol (1.5%), β-bourberene (1.1%) and α-muurolene (1.1%). Further analysis revealed that 11 sesquiterpenoids with lower rate (<1%) (Table 2), indicating that with and between populations variability. Terpenoids markers allowed detecting the presence of chemotypic variations in most of the sesquiterpenoids except for β-bourberene, α-humulene and germacrene-D.

Results of principal components analysis: Principal Components Analysis (PCA) performed on the correlations between the 11 variables yielded three eigenvectors accounting for 86% of the total variation presents in the original data. The first two of these eigenvectors explained respectively 36.3 and 30.5% of the total variation. The ordination of population`s means obtained for these two vectors is shown in Fig. 2. This analysis clustered populations in several groups.

Table 2: Means of foliar sesquiterpenes of Cupressus dupreziana in percent of total sesquiterpenes
Image for - Foliar Sesquiterpene Variations in Natural Populations of Cupressus 
        dupreziana in Tassili N`Ajjer (Algeria)

Image for - Foliar Sesquiterpene Variations in Natural Populations of Cupressus 
        dupreziana in Tassili N`Ajjer (Algeria)
Fig. 2: Ordination of the first three principal axis of Cupressus dupreziana populations

Samples obtained from the first group which concerns, Tamrit, Tifetest, Ingharouhane and Tichwinet, are characterized by high 4-α-hydroxy germacradiene levels. These populations are found in open craggy or gritty Oueds with some rare gueltas.

While in very dry gritty or craggy Oueds, populations of Tintarout and Tarout are clustered together indicating a specific group characterised by germacrene-D.

The third group that of, Tinharwida and Amazar, with high caryophyllene and α-humulene levels, are localised in dry rocky Oueds. But the fourth groups witch concerns the populations from Inelege and Tassendjoute, growing in humid, gritty soils, are characterized by γ-muurolene and γ-cadinene. Whereas Djanet planted stand population and Tidedje population of the Tassili, were found to be characterized by their bourborene and cedrol contents. All these populations showed high germacrene-D levels and low quantitative variations in all their components. Sesquiterpenoid variability reflects the heterogeneity of the genetic structure of Cupressus dupreziana populations.

The compounds found in the Tassili cypress generally resembled those previously reported to occur in some of cypress species (Zavarin et al., 1971; Rafii et al., 1992; Kim et al., 1994; Cool et al., 1998; Cool, 2005). In particular, germacrene-D and γ-muurolene were present in high relative levels. The one exception was the single population from Djanet, which has a cedrol content: similar chemotype has been observed in several North American Cupressus species (Rafii et al., 1992).

Results of cluster analysis: Genetic analysis were carried out using 11 sesquiterpens including some compounds that have been shown in other species of Cupressus to be under the control of single locus with two alleles. The dendrogram based on UPGMA clustering is shown in Fig. 3, confirms presence of the same three groups obtained from ACP analysis and emphasizes the distinctiveness of Djanet population.

This distinction is mainly based on the cedrol, germacrene-D, α-muurolene, caryophyllene and α-humulene levels. This component probably reflects the effects of environmental factors on these populations and shows how individuals have responded to ecological pressure (Yani et al., 1993).

The Djanet population was found to be very different, showing little similarity with the other populations. This population has the highest cedrol levels (11.10%). However, populations from Tassili n`Ajjer tray can be divided into two subgroups. These populations, exposed to difficult ecological conditions, namely: drought, extremely high temperature, poor soil and overgrazing, have particularly a low rate of cedrol (Yani et al., 1993). Aggregation of Tassili n`Ajjer populations into small groups is an indication of variability in this species sesqiterpenoids. The diversity of the sesquiterpene contents reflects the existence of considerable genetic variability (Forrest, 1980; Raddi and Sümer, 1999).

Image for - Foliar Sesquiterpene Variations in Natural Populations of Cupressus 
        dupreziana in Tassili N`Ajjer (Algeria)
Fig. 3: Dendrogram based Manhattan similarity distance

Genetic analysis of natural cypress populations, focusing on sesquiterpenoids, would provide a useful complement to morphological, fitness-related trait studies. Data on the genetic variability of species, based on their sesquiterpene contents, combined with information about the ecological requirements and micro evolutionary mechanisms, would be of great interest, since it would provide means of preserving and managing the natural populations.

The present analysis of Cupressus dupreziana showed the presence of considerable sesquiterpene variability within the cypress populations studied. The UPGMA analysis of terpene traits confirms this variability, but no clear-cut trends between geographical location and genetic structure can be identified on the basis of these findings.

The populations growing in Tassili n`Ajjer form a large reservoir of genetically diverse material. However, the cypress population growing in Djanet is the most highly differentiated one and has a considerable regenerative capacity. It would therefore be perfectly possible to conserve this species outside its natural territory. In the Tassili n`Ajjer itself, under the present climatic conditions, the preservation and conservation of the existing specimens may be possible, provided the harmful effects of anthropic activities are seriously reduced and controlled.

ACKNOWLEDGMENTS

The reserachers was supported by Algerian MESRS. The researchers thank Jessica Blanc for the correction of the English version and OPNT (National Park Office of Tassili) and Tergui`s guides (Lahbib, Wandoken and Ahmed Agha).

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