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Essential Oil Composition of Species in the Genus Achillea

Posted on: Thursday, 8 September 2005, 03:01 CDT

Abstract

Based on the present knowledge of essential oil composition of species belonging to the genus Achillea the factors, which may influence the composition with regard to plant biology, production and application are discussed.

According to studies from the last 15 years, a mean of 54 compounds have been identified in samples of different species. Among them, the largest number of components (149 compounds) were found in the oils of A. millefolium, A. pannonica and A. collina. The monoterpenes, 1,8-cineole, camphor, bomeol, α- and β- pinenes are among the five most abundant components. Beside chamazulene, the most frequently identified sesquiterpenes are β-caryophyllene and its oxide. The presence of chamazulene seems to remain a characteristic, but it is not ubiquitous to the members of the Millefolium group. The heritance mechanism of sesquiterpenes, especially chamazulene, seems to be established, while we know relatively less about the genetic regulation of the monoterpene compounds. During ontogenesis, major differences could be found between the stages before and after flower development. The phenological phase assuring the highest level of azulenes seems to be during flowering. Composition and compositional changes of an essential oil within the Achillea genus in different plant organs seems to depend on the species. In several cases a dominance of sesquiterpene components above the monoterpenes was found in the vegetative organs. The most important difference seems to be the lack or low amount of chamazulene as artefact in the extracts compared to the distillates.

Key Word Index

Achillea millefolium, Achillea sp., Asteraceae, yarrow, essential oil composition, taxonomy, chemotype, ontogenesis, morphogenesis, ecological factors, 1,8-cineole, camphor, borneol, chamazulene.

Introduction

Yarrow (Achillea) species may be mentioned as "evergreen" tools in therapeutic practice. Both in the ethno-pharmacology and in the up-to-date phytotherapy they assure a valuable source of natural remedies. The name of the genus might originate from the name of the Greek hero Achilles, who used this plant for curing his wound. Yarrow species were mentioned in ancient books of the Middle Ages and throughout the centuries.

The majority of the species are used in their source countries as one of the most important medicinal plants against different complaints. Today, several therapeutic applications are approved by scientific experimental results. The whole overground parts but primarily the inflorescences are effective as anti-inflammatory, spasmolytic, choleretic drugs. Essential oil and extracts of the plants are used for preparation of cosmetics, stomachic and digestive teas, creams, etc.

As yarrow species are widely known and utilized, they have also been the topic of several pharmacological, anatomical and biological investigations. In this article we want to give an overview of the state of knowledge on the essential oil composition of species of the genus Achillea and the factors which may influence it in practice.

Taxonomical Aspects & Difficulties

The genus Achillea consists of more than 120 perennial herb species being widespread in the Northern Hemisphere. A large number of species are endemic and restricted to certain regions, in contrast to other species from the genus growing over a wide geographical range.

Concerning the pharmacological significance of yarrow, the most important species belong to the group Millefolium (Table I) According to the Flora Europaea (1) this group consists of eight species, some of which (A. distans W. et K., A. millefolium L.) are divided into subspecies. The taxonomical status of species in group Distans might be questionable, belonging (1,2) or not (3,4) to the same group. Sometimes even further species may be mentioned as members of the Millefolium group (4,5). According to Ehrendorfer (6), A. ceretanica also belongs to the diploid basic species of this group. In particular cases some species had formerly been known as cytotypes or subspecies of other species (e.g. A. pratensis Saukel et Lnger). North-American or Asian species (A. lanulosa Nutt., A. borealis Bong. ) may also be identified as members of this group (7).

The group is a polyploid complex (n=9) with species from the diploid to the octoploid level. Although the chromosome number of the six major species of the group already seems to be well defined, aneuploids also often occur (3,4,8), presumably as a result of interspecific hybridization. The relative easy hybridization, vigor and fertility of the progenies could be proved in crossing experiments. In consequence, the division of the Millefolium group into "small species" does not yet seem to be scientifically solved or accepted despite to intensive efforts (6).

Table I. The Achillea species mentioned as members of the Millefolium group (section)

Determination of the correct species is also difficult even using morphological traits because hardly any proved to be stable enough. As a result of hybridization, the morphological traits may show a continuous line. The spontaneous origin of autopolyploids has also been shown (9). Furthermore, the species of this genus may exhibit phenocopies as result of an adaptation process to diverse environmental conditions.

Several Achillea taxa show a high morphological variability as a consequence of ecological effects. The unramnified forms of A. millefolium L. can easily be mistaken for A. collina Becker (10) under arid conditions. According to Gurevitch (11), the leaf dissection of populations belonging to the A. millefolium complex differs dramatically along an altitudinal gradient in the Sierra Nevada. This phenotypic variation consists of both genetic and other components.

Biste (7) described considerable variations in height, leaf width, shoot number, branching and stomata length in populations of different origin of the same species. Even the characterization of the same plant individual after re-shooting in autumn may basically differ from that of the main growth period (12). Rauchensteiner et al. (5) recently declared that the morphology of the leaflets and rayflorets were the most suitable traits for characterization of the species.

Since the classification of individual species of genus Achillea is complicated, the names and descriptors used in this review are those used by the authors of the original papers.

Characteristics of Essential Oil Composition of the Genus

Until the last decade, chamazulene used to be considered as the most important component of the essential oil and references almost exclusively dealt with characterization of its detection. In recent studies, in parallel with the development of analytical methods, we now find a more detailed analysis which results in a more comprehensive description of the total essential oil of Achillea species. According to studies from the last 15 years, a mean of 54 compounds have been identified in samples of different species (Table II). Among them, the largest number of components (149 compounds) was found in oils of A. millefolium, A. pannonica and A. collina (13).

By evaluating the published results, it can be concluded that species belonging to this genus show several similarities concerning their oil composition.

1,8-Cineole exhibits the most frequent appearance among the monoterpenes. It has been described in about one-third of the species at least in one case as main component (Table II). Besides results summarized in the table, 1,8-cineole was detected in the oils of some further species, such as A. oligochala (14), A. teretifolia (15) and A. compacta (16).

According to the published data, it can be established that besides 1,8-cineole, compounds of bornane skeleton such as camphor and borneol are among the second and third most frequently characterized components of yarrow oil (Table II). Camphor was described eight times and borneol three times as the main compound of an Achillea oil. Combinations of these monoterpenes as major components have also been frequently detected: camphor, borneol and 1,8-cineole were the main compounds in A. taygetea and A. fraasi (17), camphor and 1,8-cineole in A. albicaulis C. A. Mey. (18), A. pseudoaleppica Hub.-Mor. (19), A. pachycephala Rech.f. (20), A. talagonica Boiss. and A. vermicularis Trin (21).

α- and β-Pinenes are also among the five most often detected components, especially in the group Millefolium (22). Beside A. millefolium, the pinenes were described as main components in four other species (Table II). Hofmann (23) also mentions the monoterpenes belonging to the p-menthane (in 51%), thujane (in 23%) and pinane (17%) skeletons as being the most frequent components of the oils of the investigated A. millefolium populations.

Further compounds have occasionally been found as main components in yarrow. Thujone has been characterized in four species (Table II), notably in 70% of the oil of A. multifida (DC) Boiss. (24). Piperitone was also found in three species, ascaridole in two cases, linalool and limonene each in one species. The irregular skeletons artemisia ketone [A. ageratum L., (25); A. ligustica All., (26), A. pseudoaleppica Hub.-Mor., 19] and artemisia acetate [A. filipendulina Lam., (27)] have been found to occur in major proportions in some species.

Sesquiterpenes have been found in a considerable number of speci\es in the genus. Chamazulene has also been the object of several studies. The most frequently identified sesquiterpenes besides chamazulene were β-caryophyllene and its oxides (main component in three species), α-bisabolol and oxides, eudesmol, furthermore farnesene (each in two species). According to Hoffmann (23), sesquiterpenes are mostly characteristic to the taxa of lower (2n-4n) chromosome number, while monoterpenes to the ones of higher ploidy level. However, many other references do not confirm this generalization.

Table II. Compounds in the distilled flower-head oils of Achillea species that exceed 5% (According to references 1-110)

Table II. Compounds in the distilled flower-head oils of Achillea species that exceed 5% (According to references 1-110)

Kstner et al. (28) identified 13 substances (which may serve as additional tools for identification of plant material in Mittefolium group) because their proportions proved to be independent on external factors and constant to each-other. However, this could not spread out until now.

According to recent investigations, the significance of the enantiomeric composition in distinguishing and characterization of species is emphasized. Orth et al. (29) showed that the enantiomeric distribution of oil components depends neither on the habitat nor on the developmental stage or the method of isolation. However, as the enantiomeric ratios of the chiral monoterpenes α-pinene, β- pinene and sabinene from several Achillea species are different (29), they seem to represent taxonomically useful markers. While checking the ratios of hybrid strains of A. millefolium agg., Steinlesberger (30) found no correlation between the morphometric and enantiomeric parameters. In the future, numerous results are necessary to make a firm conclusion about the chemotaxonomical role and practical significance of optical isomers of terpenoids in yarrow oil.

Presence of Chamazulene in the Essential Oils of Yarrow Species

Until now, the majority of references have been engaged in the evaluation of chamazulene content as main component in the distilled oil. It is known to be the thermal degradation product of matricine (a proazulene) during steam distillation. As in the vast majority of literature references, there are only data on "azulene" or "chamazulene" content without mentioning and examining the type of proazulene compounds; here we are not engaged in the chemical details of the genuine guaianolides either.

Numerous studies state that the presence of chamazulene seems to remain characteristics of the members of Millefolium group (Table II). Only in exceptional cases can references be found describing chamazulene in species outside of this group: in A. ageratum L. (31), A. wilsoniana Willd. (32) or A. compacta (16).

The presence of azulenes is not a universal phenomenon for each species within the group Millefolium. Many contradictions can be found in the literature concerning the content of chamazulenes in the individual species. Beside the obvious differences in consequence of diverse isolation methods, the compositional differences seem to also have biological-genetic backgrounds, worth discussion.

Table III. Presence of azulenes in the species of the Millefolium group according to different references

Some authors declare a defined connection between the species' chromosome number and the potential for accumulation of chamazulene. Oswiecimska(33) associates the presence of chamazulenes with the tetraploid level, while she described the hexa- (A. millefolium L.) and octoploids (A. pannonica) as being azulene-free taxa. She did not, however, exclude the existence of azulene-free tetraploids, beside the azulene-containing ones which she investigated (A. collina and A. asiatica Serg.). In oils of A. asiatica, Yusubov et al. (34) and Kalinkina et al. (22) also found chamazulene. The presence of azulenes in polyploids is supposed to depend on the chemism of the original diploid species (azulene containing or azulene-free), which might be the parents of the allo- or auto- tetraploids. This was recently supported by the work of Rauchensteiner et al. (5) who described A. pratensis and A. styriaca as tetraploid species devoid of chamazulene.

Beside tetraploids, Bugge (35) established that some diploids (A. asplenifolia and A. roseo-alba) may also contain high levels of chamazulene. Studies on this latter species are scarce (28). According to morphological traits, Ehrendorfer (3) supposed that its origin could be traced back to the spontaneous hybridization of A. setacea W.et K. and A. asplenifolia among which the latter has the potential for proazulene synthesis.

During investigations on different populations belonging to the group Millefolium, Hofmann and Fritz (36) could not prove the correlation between ploidy level and presence of azulenes. They only established a decreasing tendency of chamazulene content with a growing number of chromosomes.

Lithuanian authors reported some A. millefolium L. ssp. millefolium populations having chamazulene as main compound and some others lacking of chamazulene but containing different monoterpenes as major component (β-pinene, borneol, cineole, camphor, nerolidol) (37).

Comparing the references on the chemism of yarrow, several different data can be found concerning the name of species, the number of chromosomes and presence of azulenes (Table III). The mentioned interspecific hybridization may be one of the reasons why the definition and chemical characterization of certain taxa is often contradictory. Orth et al. (38) investigated five distinct taxa of which three could be defined as A. collina Becker and containing chamazulene, while one chamazulene-free triploid and a chamazulene-rich diploid were concluded to be spontaneous hybrids. Also, Dabrowska (8) reported a tetraploid chamazulene containing taxon which might also be of hybrid origin, according to morphological traits. Earlier, Ttnyi (39) noted in his chemotaxonomical review that seven of the mentioned 13 Achillea species were both azulene-free and azulene-containing according to different references. As result of recent investigations Radusiene and Gudaityte (40) supposed that the rapid identification ofproazulene-containing plants might be solved according to their productivity.

In numerous analytical reports the exact definition of the taxon seems to be missing. Presumably, the description of the taxa was carried out according to insufficient botanical-systematical examinations, as presumed also by Kastner et al. (28). These investigations have given rise to confusing results: the chamazulene content of A. millefolium oil varying between 0% and 85% (41-48).

We can generally conclude that in the group Millefolium the accumulation of azulenes seems to be restricted to A. asplenifolia (2n), A. roseo-alba (2n) and A. collina (4n), while azulenes are absent in A. setacea W.et K. (2n), A. millefolium (6n) and A. pannonica (8n). Results which do not agree with these findings might be traced back to the false definition of the species focusing on morphological traits in the extremely variable group Millefolium without chromosome counting; or on the contrary, focusing on chromosome numbers and mistaken polyploids of azulene-free and azulene containing diploid taxa.

Chemotaxonomic Aspects of Essential Oil Variability

Today the existence of intraspecific chemical variability concerning essential oil composition seems to be a well known phenomenon which must be taken into consideration both theoretically and practically. In principle both qualitative (components present or absent) and quantitative (components in considerably different proportions) chemical races might be present within a species (39). The species of the genus Achillea may serve as examples for both. At the same time the increased sensitivity of analytical methods drastically decreases the limit of detection and as a result, several taxa have become only quantitatively distinguishable, in contrast to previous examinations where qualitative differences had been described.

From the cited references it can be concluded the number of the identified main components ranges from one to three compounds in the majority of species. In most cases these different chemical races had been detected separately and mentioned by different authors which makes the comparison and evaluation of data more complicated. Of course, the number of the reported main components in the oil may to some extent also depend on the frequency of investigations of the target species. In the oil of the most often investigated taxon called "A. millefolium," 10 different main components could be found according to the different references (Table IL).

Evaluation of distinct chemotypes within the same study is rarely found, but the first results were reported 40 years ago: populations of A. asplenifolia Vent. devoid of or possessing a low or high content of chamazulene had been described by Tyihk et al. (49).

Hthelyi et al. (50) investigated the most characteristic components of 220 different Achillea populations from Hungary belonging to nine species. In each species (except A. ptarmica), at least three chemical varieties had been identified according to the main terpenoid components. Among others, for A. ochroleuca, three types (a linalool+borneol+bornylacetate+cubebene type; another linalool+borneol+bornylacetate+elemol+eudesmol type and a third one containing more than 75% eudesmol) were described. Also considerable differences had been found in other reports in the oil profiles (linalool, achillenol and lavandulol types) in A. distans W. et K. populations from six areas (51), and recently of A. millefolium L. ssp. millefolium populations from 11 areas (37).

A considerable lack of information also originates from the fact that investigations dealing with intraspecific chemical diversity most often descr\ibe the differences between populations without referring to the individual variability within populations.

In our investigations on A. crithmifolia W. et K. based on samples of individual plants it was established that three kinds of quantitative chemotypes could be differentiated and their proportions might be characteristic for the growing area. While in the 'Matra' mountain in Hungary, 60% of individuals were found with camphor as their main component, in the 'Visegradi' mountain region, the majority (55%) of plants belong to the cineole type and in the population of 'Brzsny' mountain, mainly the "mixed" type individuals were found (52). Similar distributions were also found for A. ochroleuca Ehrh.: three chemotypes (borneol, borneol+α- bisabolol; and an unidentified sesquiterpene compound) were described having been found in different locations of the same hill near to Budapest (53).

In the genus Achillea, especially in the Millefolium group, a wide variation in azulene accumulation, and both qualitative (azulene-free or azulene containing) and quantitative (low or high level of azulene) chemotypes can be distinguished. The definition of any taxon as an intraspecific chemotype in the group Millefolium, however, may only be accepted if the taxon is identified by several means and is characterized in detail.

A good example for this complex approach seems to be the work of Rauchensteiner et al. (5). They provided one of the most comprehensive recent evaluations of 10 taxa belonging to the Millefolium group. The study includes detailed morphological, cytological and chemical traits. Especially in the case of A. pannonica, A. distans W. et K. and A. millefolium. it was proved that the direct definition of the species according to the oil compounds was not possible and that it was also necessary to include suitable morphological characteristics.

The degree of chemical variability of a taxon seems to be specific for the species. For the exact evaluation of intraspecific variability we need to identify the homogeneity of populations, evaluate the morphological, taxonomical and genetic considerations and determine the effect of any further influencing factor.

Biotic and Abiotic Factors Influencing the Actual Results of Chemical Evaluation

The problems of taxonomical characterization and the difficulty of determining the lowest detectable quantity, and in consequence the presence of any component, has been mentioned above. The chemical fingerprint of each taxon is also influenced by several biotic and abiotic factors, however. It seems useful to summarize the scientific results on the background of the existence, direction and strength of these effects.

Genetic background: Examinations concerning the genetic background of oil components in the genus Achillea can be divided into two parts. Heritance mechanisms of the sesquiterpenes and especially chamazulene seems to be almost accepted while we know relatively less about the genetic regulation of the monoterpene compounds.

In a five-year study Pter et al. (54) proved that the proazulene content of A. millefolium could be increased by positive selection, but they found that very high contents could not be stabilized by this method.

The most comprehensive work related to sesquiterpenes (eudesmanolides, longipinanes and guaianolides) of yarrow was carried out by Vetter et al. (55,56). Based on interspecific crossings and backcrossing with evaluation of the progenies they established, that biosynthesis into the direction of guaianolides from intermediates is promoted by the recessive allele of a single gene pair. In the proazulene containing tetraploid genome the recessive condition of a single locus may already assure the production of azulenes, but its quantity is influenced by a second locus. According to experimental results in the related chamomile, synthesis of proazulenes may also be promoted by recessive alleles and modifying polygenes are supposed to regulate the quantity of it (57,58).

Data on the inheritance of monoterpenes are rather scarce. As mentioned above, 1,8-cineole, camphor and borneol are the most common monoterpene components of the oil in the genus.

In our work with A. crithmifolia W. et K., we studied the genetic determination of main components camphor, borneol and cineole byintraspecific crossings among individuals belonging to different chemotypes as well as by selfings. According to the segregation of F^sub 1^ and F^sub 2^ progenies, there is only a quantitative variability in case of these compounds as we had not detected any plant individual lacking of any of the studied components. However, there was a wide range in the relative percentages of the main compounds in the oil (59). The results show, that monogenic determination may practically be excluded and in place a regulation by three to four loci or a polygene system is expected. According to the data of the evaluation of several hundred individuals in the progenies, narrow sense heritability was calculated to be medium (0.52) for camphor and low (0.12 and 0.28) for 1,8-cineole and borneol, respectively.

The results indicated that chemotypes were segregated also in the case of selfing and only after three cycles of selfing a more homogenous population starts to develop. It means that these chemotypes may not exist as true homozygotic genotypes. Heterozygotic structure of individuals and segregation of selfed and F^sub 1^ progenies concerning oil composition have also been described by Vetter (55) in A. ceretanica Sennen, A. pratensis Saukel and Lnger, A. distans W. et K. subsp. styriaca and A. collina Becker.

In other species, the inheritance of borneol and 1,8-cineole had been investigated only in Hedeoma drummondii from which it was concluded that a two loci determination for borneol and a four loci determination for 1,8-cineole existed (60). Data on the inheritance of camphor can be found for the related Tanacetum vulgare based on the results of Forsn (61), Lokki et al. (62) and later Holopainen et al. (63). It was determined that biosynthetic routes among camphor and thujone were regulated by two loci with two alleles each in epistasis with a third locus of three alleles. However, if the synthesis of any common compound is going on through the same biosynthetic route and regulated by the same genes in each species is not yet clear.

Ontogenesis: It seems to be rather difficult to form a general statement about the accumulation tendency of monoterpenoid compounds during ontogenesis because the investigations have been focused on different species and compounds making a comparison difficult if not impossible.

The most frequently studied species, A. millefolium was investigated in detail by Shalaby (64) who established a continuous increase of α-pinene from the vegetative stage until budding while the levels of β-pinene, 1,8-cineole, borneol and β- caryophyllene decreased from the initial phases until budding, after which they started to increase. Compositional changes in the oil of A. millefolium during plant development were studied recently by Rohloff et al. (65). Partly in contrast to the previously mentioned data, here the levels of both α- and β-pinenes as well as α-thujone were increasing, while those of sabinene, bornyl acetate and borneol decreased during development.

The examinations of Cernaj et al. (66) provide some data on the accumulation tendencies of monoterpene compounds during ontogenesis of A. collina. In the proportion of the studied four monoterpenes (α- and β-pinene, limonene, sabinene) major differences were only found in the stages before and after the generative differentiation with a maximum level at developed bud stage; however, the levels did not change much during the flowering process that followed.

Similarly, in A. ochroleuca Ehrh. major differences could be found between the stages before and after flower development (53). At the early stages sesquiterpenes comprised the major part of the oil (72%), but after shoot formation the proportion of monoterpenes increased to a maximum level at full flowering (60%) with borneol being the major compound of the oil. A very similar tendency was also proved for A. pannonica (53), but the individual compounds were different and characteristic for the species. In A. pannonica the main monoterpenes were represented by α-pinene and 1,8-cineole in place of borneol (Figure 1). Decreases of the sesquiterpene compound germacrene D and characteristic changes of β-pinene, 1,8-cineole and camphor were measured during flower development of A. millefolium ssp. millefolium by Figueiredo et al. (67).

A change in the monoterpene composition during ontogenesis could be observed also in A. crithmifolia W. et K. From the leaf rosette stage until full flowering the proportion of main components camphor and borneol increased, however this tendency was specific only for the camphor chemotype (68).

As for the sesquiterpenes, in the genus Achillea a special attention has been paid to the accumulation of azulenes during ontogenesis. Previous reports do not fully agree which phenological phase assures the highest level of azulene formation. In a taxon described as A. millefolium Ruminska (69) and Ustoysanin et al. (48) detected a maximum accumulation level at the white bud stage. According to their explanation, the oil ducts are already fully developed at this phase and further synthesis is not known in the following stages. Figueiredo et al. (67) also reported decreasing chamazulene content throughout the development of flower heads. In other investigations the maximum level of azulenes and β- caryophyllene could be measured at full flowering in A. collina Becker (66) or at the end of flowering in A. millefolium (31).

The leaves show a particular pattern of accumulation during their development: in A. millefolium the proportion of azuleneswas about 10 times higher in the young leaves than in the older ones (69).

No direct explanation for these changes in the oil composition of yarrow species is known, but changes in activity of regulating genes and/or enzymes can generally be supposed. On the basis of recent biochemical results, Bach (70) presumed that the function and activity of isoenzymes catalyzing mevalonic acid synthesis and the determining gene families are under a significant ontogenetic and/ or ecological influence. Similar regulation might be supposed in the following biosynthetic steps.

Figure 1. Changes in the composition of the oil of A. pannonica Scheele during ontogenesis

The contribution of ontogenesis to the changes in oil composition can be partly attributed to the different oil components found in the vegetative organs (predominantly leaves) and the reproductive organs (predominantly flowers). Thus, in principle, ontogenetic differences may at least partially be traced back to the different anatomical structures of the accumulation organs. In other Asteraceae species it was proved by anatomical investigations that the accumulation structures of the leaves may change during the developmental stages and they are represented by mainly different compositions (71).

The observations on the separation of mono- and sesquiterpenoids in different developmental phases may be in accordance with the findings of McCaskill and Croteau (72), who concluded that during the intensive growth period the precursor flow distributes between the cytoplasm (sites of sesquiterpene synthesis) and plastids (sites of monoterpene synthesis) while after full development of the cell the majority is utilized in the plastids.

Morphogenesis: Composition and compositional changes of oils within the Achillea genus in different plant organs seems to be dependent on the individual species.

Figueiredo et al. (43) detected practically equal levels of 1,8- cineole in the flowers (28.7%) and in the upper leaves (24.5%) in samples of a taxon defined as A. niillefoliuin ssp. millefoliwn. At the same time, the accumulation level of sabinene belonging to the thujane skeleton group was three times higher in the flowers than in the leaves. A similar oil composition of the flowers, leaves and stem in A. millefolium was reported by Eglseer (73) and Orav et al. (46); however, only six of the investigated 11 populations showed this phenomenon in a recent Lithuanian study (37). Moreover, Cernaj et al. (74) proved that compositional differences exists even among solvent extracts from different parts of inflorescences. In A. nobilis L. the main component of the oil differs according to the organ i.e. in the inflorescences piperitone could be found while in the leaves borneol was detected (50).

In several cases, higher levels of sesquiterpenes compared to the monoterpenes were found in the vegetative organs. To a certain extent it may be supposed to be a general tendency throughout the genus. In A. ptarmica L. the main sesquiterpene component farnesene was present by a 20% higher level in the leaves than in the flowers (75). As a further example the proportion of the sesquiterpene β-cubebene showed a notable difference at 15% in the leaves and only 7% in the flowers of A. crithmifolia W. et K. (52). In our investigations this phenomenon was also proved for A. pannonica Scheele and A. ochroleuca Ehrh. The main component of their leaves was β-cubebene and α-bisabolol or a further, unidentified sesquiterpene compound (53). In contrast, some monoterpene compounds could be found only in the generative parts: ascaridole in A. ochroleuca and β-pinene in A. pannonica while the proportion of 1,8-cineole was found at a higher level in the generative organs in both species. In this context the compositional differences betweeen organs follow ontogenetic development. In A. millefolium Rohloff et al. (65) also established an increase of monoterpenes in relation to sesquiterpenes between the vegetative and generative developmental stages.

Chamazulene does not follow this pattern of segregation. According to several investigations the maximum level of chamazulene can be measured in the apical flowering parts (23,31,76,77). In A. millefolium Ustojsanin et al. (48) measured a seven fold higher level of chamazulene in the flowers than in the leaves during the same phenological phase (budding). The maximum levels of chamazulene were measured at the same time as the maximum accumulation of oil in these experiments.

In contradiction with the above noted findings, the results of a recent analysis of A. millefolium s. L. clones and the cultivar 'Proa' indicated that there was no significant difference between the chamazulene contents of the leaves and flowers; however, it was found to be almost 10 times lower in the stems (22). Formerly, Tyihk and Vgujfalvi (78) and Eglseer (73) also described a similar composition in the flower and leaf oils of A. millefolium. In our own investigations on a collection of 28 wild populations of A. collina it was established that the leaves may contain approximately the same level of chamazulene as flowers and a medium strong significant correlation was proved between them (r=0.7) (79).

An explanation for the described accumulation tendencies might be the correlation between the site of secretion and activity of specific terpenoid compounds. In the flowers and leaves different proportions of endo- and exogenous ducts may be present. According to Loomis and Croteau (80), the compounds in endogenous cells may be more actively involved in further biosynthetic transformations than the ones secreted in exogenous ducts.

It was presented by McCaskill and Croteau (72) that cells with an abundance of endoplasmic reticule and having few plastids may represent the sites of sesquiterpene synthesis while the cells of the mezophyll origin containing many plastids are the main sites of monoterpene biosynthesis. It is, however, more likely that the distribution of different oil components between different organs can only be partly traced back to this intracellular differentiation. Details about the secretory processes, the transfer of synthesized terpenoid products and their possible catabolism are poorly understood today.

Nevertheless, morphogenesis and organic differentiation seems to be a basic factor in assuring the characteristic composition of the species: it was proved by Figueiredo et al. (81) that the composition of the oil of undifferentiated cell suspension cultures was markedly different from that of the parent plant.

Environmental effects: The effect of ecological factors on the composition of yarrow oil has been investigated with respect to the accumulation of azulene compounds.

Earlier publications in the 50s and 60s indicated the favorable effect of a warm climate and stronger irradiation on the formation of proazulenes (49). However, even in that period some authors mentioned that presence or absence of azulenes could not be explained only by ecological effects but they might be responsible for the quantitative level (49,82). In contrast to certain data the majority of authors agree that the accumulation of oil may be much more influenced by ecological factors than its composition (78,83).

Genotypic determination of the accumulation of azulenic compounds seems to be the accepted theory. Hofmann and Fritz (36) proved that the content of chamazulene in Achillea collina cv. 'Proa' was not influenced by either the quantity of precipitation or fluctuations of the temperature and duration of sunshine or intensity of irradiation. Achillea collina Becker has been investigated also in another experiment and studied in parallel in Slovakia and Finland. Although plant habits such as height, mass, proportion of organs and oil production were influenced by the edaphic and climatic conditions of the experimental sites, the chamazulene content of the oil remained constant (84). The study of 72 natural populations of Achillea millefolium and A. collina revealed that the plants rich in chamazulene can be found in special meadow-associations on soils assuring a definite level of nutrients (85). In a similar study in Lithuania, the highest percentage of proazulene containing plants could be found in woodland and shrubland habitats (40). It seems that the presence of azulenes, however, is not the result of habitat but rather that the habitat offers appropriate environmental conditions for the propagation of proazulene containing genotypes.

Two populations of A. millefolium ssp. millefolium in different habitats were compared by Figueiredo et al. (67) and considerable differences in the main oil components were found. The differences were supposed to be results of different nutrient levels in the soil and/or the period of insolation without any further proof. Recently, the special effect of altitude has been investigated on the oil composition of A. millefolium (86). Significant changes in the proportion of lavandulyl acetate, β-caryophyllene, α- humulene, γ-curcumene +germacrene D and chamazulene have been found according to habitat at different altitudes. In particular, the absence of α- and β-thujones was noted being of major importance concerning their potential toxic effect. However, the proportions of the above mentioned components were rather low (0.13- 7.73%) and the effect of altitude is not fully independent of other ecological factors.

Generally, in open field experiments it is difficult to isolate the effect of individual factors such as temperature, light, water, and nutrient supply from the rest of the environment. In case of A. crithmifolia the effect of temperature and illumination has been investigated on the composition of the oil under controlled conditions. No qualitative changes could be detected in the main components of the oil when growing the plants under "warm" and "cold" condition\s (52), but quantitative differences were detected as a result of the 3-5C higher temperature regime and higher illumination rate: the proportions of bornane derivatives (camphor, borneol) were found at 10-20% higher levels, while the proportion of 1,8-cineole decreased by 8-10%.

Similar findings are known in the case of other essential oil plants. Under a controlled environment, the oil of individuals of Salvia officinalis and S. austriaca showed an increase of borneol and camphor as result of higher temperature regimes (87). In support of this concept Burbott and Loomis (88) proved the enhancing effect of warm nights on the oxidation processes. Under these circumstances the proportion of menthofuran and pulegone was increased in Mentha piperita. These differences were most likely caused by changed enzymatic processes.

Oil isolation and storage: The method of oil isolation may play a considerable role in the final composition and quality of the oil of Achillea as is the case for other species.

The significance of isolation method has been known first in case of chamazulene, which does not exist in the living plant tissue but is formed during hydrodistillation. Its precursor, matricine, has been the subject of intensive investigations. To obtain a rough estimate of matricine content, Vuorela et al. (89) established an optimized headspace-gas-chromatography (HSGC) technique.

The main components of A. crithmifolia extract differ significantly in consequence of the isolation method. Cold pentane- extract showed the poorest range of components (Table IV). The product of the supercritical CO2 extraction seems to be qualitatively comparable with the traditional hydrodistillation; however, the proportion of the components is regularly different (90). A composition most similar to the distilled oil could be produced at a pressure of 140 Bar.

Rohloff et al. (65) investigated the composition of solidphase microextracts compared to distillates. It was found that SPME resulted in higher levels of α-bisabolol, β-bisabolene and δ-cadinene as compared to steam distilled samples.

Table IV. Main volatile components of the flowers of Achillea crithmifolia W. et K. as result of different isolation methods (90)

Similarly, a diethyl ether extract of A. millefolium contained fewer components (70 compounds) than the distilled oil (107 compounds) (23). There were also qualitative differences: the distillate contained more oxygenated components while more hydrocarbons were present in the extract. The most important difference seems to be the lack or low amount of chamazulene in the extracts compared to the distillates (23,44,91) as chamazulene is formed during distillation.

The content of chamazulene in the distilled oil of A. millefolium was found to depend on the duration of distillation. After 3 h distillation the chamazulene content detected in the distillate was 80% of the amount measured after 6 h (44). Sometimes considerable differences between reported studies exist. In the investigations of Grahle (23) 88% of chamazulene had been detected in the first 9 h and 30 h distillation time was needed to yield all of it. During such a long time period some other components may also be transformed to different artefacts and/or become volatilised. Hofmann (23) reported that several mono- and sesquiterpene derivatives (e.g. linalool oxides, p-cymene, β-caryophyllene) might originate as artefacts during distillation.

The number of investigations on the effect of storage seems to be considerably lower. Some former investigations described a significant decrease of proazulenes already after a three months storage (76); however, according to the majority of reports, the storage of yarrow up to two and a half years does not cause any significant changes in the proportion of chamazulene in the distilled oil (23,31,73).

The storage of the distilled oil may have more influence on the composition of the oil than storage of the crude drug. In the oil, monoterpenes seem to suffer more significant changes during storage time because of their volatility, resinifization and rearrangement potential while the less volatile sesquiterpenes are less affected. During of the oil storage for one year the proportion of monoterpenes decreased from 14% to 1% and the most characteristic change was registered for sabinene (23).

Conclusions

The species of genus Achillea represent an important tool in herbal therapy. Until the last decade, chamazulene used to be considered as the main component of the distilled oil and investigated most comprehensively. Recently, more detailed analysis of the total oil of Achillea species have been published. The taxonomical role and practical significance of chiral isomers of terpenoids in yarrow oil is still a question, which desires further efforts. Several Achillea species seem to exhibit a considerable intraspecific chemical diversity, which have been proved by examinations on diverse populations; however the individual variability within an area or plant stand is rarely studied.

A complex and universally accepted determination of the taxon of optimal content of active ingredients is lacking even today. This problem arises first of all in the group Millefolium. The contradictious descriptions seem to have biological, genetic and analytical backgrounds. In order to assure a stable and optimal quality of yarrow drugs, the main efforts should be focused on:

* determination of the most effective components of the oil;

* description of special markers (coenological, morphological, cytological or any other traits) connected with active ingredients;

* breeding of new varieties assuring the desired oil composition.

It seems that yarrow species have to keep their place on the palette of herbal remedies, but for the future, the source of raw plant seems to be assured from controlled production instead of collection from the wild.

References

1. T. G. Tutin, W. H. Heywood, N. A. Surges, D. M. Moore, D. H. Valentine, S. M. Walters and D. A. Webb, Flora Europaea Vol. 4 Plantaginaceaeto Asteraceae. Cambridge Univ. Press, Cambridge, London, 159-165 (1976).

2. G. Hegi, Illustrierte Flora von Mitteleuropa. Band 6. Teil 3. (G. Wagenitz) 310-346, Verlag Paul Parey, Berlin-Hamburg (1979).

3. F. Ehrendorfer, Probleme, Methoden und Ergebnisse tier experimentellen Systematik. Planta Med., 3, 234-251 (1963).

4. J. Daniheka. and O. Rotreklov, Chromosome numbers within the Achillea millefolium and A. distans groups in the Czech republic and Slovakia. Folia Geobotanica, 36, 163-191 (2001).

5. F. Rauchensteiner, S. Nejati, I. Werner, S.Glasl, J. Saukel, J. Jurenits and W. Kubelka, Determination of taxa of the Achillea millefolium group and Achillea crithmifolia by morphological and phytochemical methods I. Characterization of Central European taxa. Sci. Pharm., 70, 199-230 (2002).

6. F. Ehrendorfer, Die Systematik der Millefolium Gruppe. Drogenreport, 11, 30-44 (1998).

7. C. Biste, Zytotaxonomische Untersuchungen des Formenkreises Achillea millefolium (Asteraceae) in der DDR. Feddes Repertorium, 88, 533-613 (1978).

8. J. Dabrowska, Observations concerning distribution of azulene containing and azuleneless forms of Achillea L. in Silesia as compared to the distribution of individual taxa of the genus in this region. Herba Pol., 1, 40-69 (1972).

9. U. Kastner, ber Proazulene und verwandte Sesquiterpene- Laktone in verschiedenen Taxa der Achillea millefolium Gruppe. Diss. Univ. Wien (1991).

10. J. Dabrovska, Observations of the fruit size of nine taxons from the genus Achillea L. representing natural di-, tetra-, hexa- and octaploids. Herba PoL, 28(23), 55-66 (1977).

11. J. Gurevitch, Variation in leaf dissection and leaf energy budgets among populations of Achillea from an altitudinal gradient. Amer. J. Bot., 9, 1298-1306 (1988).

12. J. Saukel and R. Lnger Achillea pratensis Saukel and Langer.spec. nova eine tetraploide Sippe der A. millefolium Gruppe. Phyton (Horn), 32, 159-172 (1992).

13. L. Hofmann, D. Fritz, S. Nitz, and F. Drawert, Essential oil composition of three polyploids in the Achillea millefolium 'Complex'. Phytochemistry, 32, 537-542 (1992).

14. Z. Toker, H. C. zen, R. A. Clery and N. E. Owen, Essential oils of two Achillea species from Turkey. J. Essent. Oil. Res., 15, 100-101 (2003).

15. M. Unlu, D. Daferera, E. Donmez, M. Polissiou, B. Tepe and A. Sokmen, Compositions and the in vitro antimicrobial activities of the essential oils of Achillea setacea and Achillea terenifolia. J. Ethnopharmacol., 83, 117-121 (2002).

16. A. Kowalczuk, J. Dabrowska and A. Nosal, Comparative analysis of the composition of volatile oil of yellow flowered yarrow Achillea ageratum L. and Achillea compacta. Herba Pol., 44 (2), 114- 120 (1998).

17. P. Magiatis, A. L. Skaltsounis, I. Chinou and S.A. Haroutounian, Chemical composition and in vitro antimicrobial activity of the essential oils of the greek Achillea species. Z. Naturforsch., 57, 287-290 (2002).

18. A. Feizbakhs, M.S. Tehrani and A. Rustaiyan, Composition of the essential oil of Achillea albicaulis C. A. Mey. J. Essent. Oil Res., 15, 21-22 (2003).

19. H. C. zen, Z. Toker, R. A. Clery and N. E. Owen, Composition of the essential oil of Achillea pseudoaleppica. Hub-Mor. J. Essent. Oil Res., 15, 96-97 (2003).

20. S. Bamasian, A. Rustaiyan and S. Masoudi, Chemical constituents of the essential oil of Achillea pachycephala Rech.f., a species endemic to Iran. 33rd Internat. Symposium on Essential Oils, Abstracts, p. 50 (2002).

21. A. Rustaiyan, H. Komeilizadeh, M. S. Shariatpanahi, A. Jassbi, and S. Masoudi, Comparative study on the essential oils of three Achillea species from Iran. J. Essent. Oil Res., 10, 207-209 (1998).

22. G.I. Kalinkina, A. D. Dembisky, and T. P. Berezovskaya, Chemical composition of essential oils of Achillea species from Siberia. Khimiya Rastitelnogo Syrya, 3, 13-18 (2000).

23. L. Hofmann, Einfluss von Genotyp, Ontogenese \und usseren Faktoren auf pflanzenbauliche Merkmale sowie athensche le und Flavonoide von Klonen der Schafgarbe (Achillea millefolium Aggregat). PhD Thesis, Technische Universitt, Mnchen (1993).

24. K. H. Baser, B. Demirci, F. Demirci, S. Kocak, C. Akinci, H. Malyner and G. Guleryu, Composition and antimicrobial activity of the essential oil of Achillea multifida. Planta Med., 68, 941-943 (2002).

25. R. Puerta, M. T. Saenz, M. D. Garcia and R. Puerta, Antibacterial activity and composition of the volatile oil from Achillea ageratum. Phytother. Res., 10, 248-250 (1996).

26. M. Maffei, F. Germano, G. Doglia and F. Chialva, Essential oils, chromosome numbers and karyotypes from Italian Achillea species, Part II. J. Essent. Oil Res., 5, 61-70 (1993).

27. T. Wenham and J. Birkby, Composition of Achillea filipendulina essential oil. 33rd Internat. Symposium on Essential Oils, p. 192 (2002).

28. U. Kstner, J. Saukel, K. Zitterl-Eglseer, R. Langer, G. Reznicek, J. Jurenitsch and W. Kubelka, therisches l- ein zustzliches Merkmal fr Charakterisierung der mitteleuropaischen Taxa der Achillea millefolium-Gruppe. Sci. Pharm., 60, 87-99 (1992).

29. M. Orth, D. Juchelka, A. Mosandl and F. Ch. Czygan, Enantiomere Monoterpene im atherischem l von Achillea millefolium s.l. - eine zusatzliche taxonomische Bestimmungshilfe? Pharmazie, 55, 6, 456-459 (2000).

30. H. M. Steinlesberger, Investigations on progenies of crossing experiments of Bulgarian and Austrian yarrows (Achillea millefolium Agg. Compositae) with focus on the enantiomeric ratios of selected monoterpenes. PhD Thesis, Veterinrmedizinische University, Vienna (2002).

31. V. Kosova, Beitrag zur pharmacognostischen Bewertung einiger Arten der Gattung Achillea. Acta Facultatis Pharm. Brunensis et Bratislavensis, 2, 71-100 (1959).

32. K. Ma, Q. Meng and J. Ren, The constituents of the volatile oil from Achillea wilsoniana. Zhong Yao Cai, 20(4), 193-194 (1997).

33. M. Oswiecimska, Korrelation zwischen Chromosomenzahl und Prokamazulenen in Achillea von Osteuropa. Planta Med., 25, 389-394 (1974).

34. M. S. Yusubov, G.I. Kalinkina, L.A. Drygunova, L.M. Pokrovsky, E.A. Korolyuk and A.V. Tkachev, Chemical composition of Achillea millefolium L. and A. asiatica Serg. essential oils. Khimiya Rastitelnogo Syrya, 3, 25-32 (2000).

35. G Bugge, Untersuchungen der Sippen des Achillea millefolium Komplexes auf Azulengehalt und Ploidiegrad. Angew. Botanik, 65, 331- 339 (1991).

36. L. Hofmann, and D. Fritz, Quality of the essential oil of different types of the Achillea millefolium 'Complex.' Acta Hort., No. 330, 153-156 (1993).

37. D. Mockut and A. Judzentien, Chemotypes of the essential oils os Achillea millefolium L. ssp. millefolium growing wild in Eastern Lithuania. Chemya, 13(3), 168-178 (2000).

38. M. Orth, F. Czygan, and V. P. Dedkov, Variation in essential oil composition and chiral monoterpenes of Achillea millefolium from Iran. J. Essent. Oil Res., 11, 681-687 (1999).

39. P. Ttnyi, Infraspecific chemical taxa of medicinal plants. Akadmiai Kiad, Budapest, (1970).

40. J. Radusiene and O. Gudaityte, Distribution of proazulenes and productivity in Achillea millefolium s.l. spontaneous populations. Abstracts of ISMAP, Campinas, Brasil, July, 5-8, A01- 10, (2004).

41. S. Afsharipou, S. Asgary and G. B. Lockwood, Volatile constituents of A. millefolium from Iran. Flav. Fragr. J., 11, 265- 267 (1996).

42. A. Blanger and L. Dextraze, Variability of chamazulene within Achillea millefolium L. Acta Hort., Nr. 330, 141-145 (1993).

43. C. Figueiredo, J. Barroso, M. S. Pais, and J. J. C. Scheffer, Composition of the essential oils from leaves and flowers of Achillea millefolium. Flav. Fragr. J., 7, 219-222 (1992).

44. J. Hachey, G. Collin, M. Gagnon, G. Vernin and D. Fraisse, Exraction and GC/MS analysis of the essential oil of Achillea millefolium complex. J. Essent. Oil Res., 2, 317-326 (1990).

45. S. Ksmenoglu, B. Demirci, F. Demirci and H. K. C. Baser, The essential oil composition of Achillea coarctata Poir. Abstracts of the 28th ISEO, Eskisehir, Turkey, p 37 (1997).

46. A. Orav, T. Kailas and K. Ivask, Composition of the essential oil from Achillea millefolium from Estonia. J. Essent. Oil Res., 13, 290-294 (2001).

47. J. Pino, A. Rosado and V. Fuentes, Chemical composition of the leaf oil of Achillea millefolium grown in Cuba. J. Essent. Oil Res., 10, 427-428 (1998).

48. A. Ustoysanin, D. A. Konovalov, A. I. Sreter, O. A. and K. S. Ribalko, Content of chamazulenes in Achillea millefolium in European parts of the Sowiet-Union. Rasztit. Nauki, 3, 424-429 (1987).

49. E. Tyihk, I. Mth, J. Svb, and R Ttnyi, Untersuchungen ber die Azulenverbindungen der Achillea Arten. Die Pharmazie, 17, 563-571 (1963).

50. . Hthelyi, B. Dnosand P. Ttnyi, Phytochemical studies on the essential oils of species belonging to the Achillea genus, by GC/ MS. Biomed. Environm. Mass Spectr. 18, 629-636 (1989).

51. . Hthelyi, R Ttnyi, R Kaposi, B. Dnos, Zs. Kernczi, Gy. Bki, and I. Koczka, GC/MS investigation of antimicrobial and repellent compounds. Herba Hung., 27, (2-3), 89-95 (1988).

52. . Nmeth, J. Bernth and G. Tarjn, Essential oil composition of Achillea crithmifolia: I. Identification of chemovarieties grown in wild populations. J. Essent. Oil. Res., 5, 349-357 (1993).

53. N..Zmborin, Achillea fajok szaporodsbiolgiai s kemizmus vizsglata. Gygyszerszet (Congressus Pharmaceuticus Hungaricus X. Budapest, Abstracts p. 16 (1996).

54. M. H. Pter, E. Rcz-Kotilla and G. Rcz, Breeding experiments on Achillea millefolium, results of the period of 1975-1980. Revista Medicala, 28(2), 188-191 (1982).

55. S. Vetter, Kreuzungsexperimente mit tetraploiden Sippen der Achillea millefolium Gruppe: Sesquiterpene und morphologische Merkmale hybridogener F1 Populationen im Vergleich. Linzer Biol. Beitr, 27(2), 1161-1211 (1995).

56. S. Vetter, Ch. Franz, S. Glasl, U. Kastner, J. Saukel and J. Jurenits, Inheritance of sesquiterpene /actone types within the Achillea millefolium complex (Compositae). Plant Breed., 116, 79-82 (1997).

57. P. Ttnyi, ber das Problem der intraspezifischen chemischen Taxa von Matricaria chamomilla. Pharmazie, 16, 273-378 (1961).

58. Ch. Franz, and I. Wickel, Zur Vererbung der Bestandteile des Kamillenols - Qualitative Vererbung von Chamazulen und Bisabolol. Herba Hung. 24, (2-3), 49-59 (1985).

59. . Nrneth, J. Bernth, and . Hthelyi, Chemotypes and their stability in Achillea crithmifolia W.et K. populations. J. Essent. Oil Res., 12, 53-58 (2000).

60. S. Irving, .and R. R Adams, Genetic and biosynthetic relationships of monoterpene, In: Terpenoids, structure, biogenesis and distribution. Edits., E.C. Runeckless, and T. J. Mabry, Vol.6., 187-214, Academic Press, New York (1973).

61. K. Forsen, ber die infraspezifische chemische Variation bei Chrysanthemum vulgare. Ann. Acad. Scient. Fennicae, Helsinki, Series A, IV. Biologica, 207(1975).

62. J. Lokki, M. Sorsa, M. Forsen and M.v. Schantz, Genetics of monoterpenes in Chrysanthemum vulgare I. Genetic control and inheritance of some of the most common chemotypes. Hereditas, 74, 225-232 (1973).

63. M. Holopainen, R. Hiltunen, J. Lokki, K. Forsen and M. Schantz, Model for the genetic control of thujone, sabinene and umbellulone in tansy (Tanacetum vulgare). Hereditas, 106, 205-208 (1987).

64. A. S. Shalaby, Essential oil content, composition and biosynthesis in Achillea millefolium ssp. collina Becker. PhD. Thesis, Medical University, Budapest (1978).

65. J. Rohloff, E. B. Skagen, A. H. Steen and T. H. Iversen, Production of yarrow (Achillea millefolium L.) in Norway: essential oil content and quality. J. Agric. Food Chem., 48, 6205-6209 (2000).

66. P. Cernaj, H. Liptkov, G. Mohr, M. Repck and R. Honcariv, Variability of the content and composition of essential oil during ontogenesis of Achillea collina. Herba Hung., 22 (1), 21-27 (1983).

67. A.C. Figueiredo, J.G.Barroso, M.S.S. Pais and J.J.C. Schetfer, Composition of the essential oils from two populations of Achillea millefolium L. ssp. millefolium. J. Chromatogr. Sci., 30, 392-395 (1992).

68. . Nrneth, J. Bernth and E. Hthelyi, Diversity in chemotype reaction affected by ontogenetical and ecological factors. Acta Hort., No. 344, 178-187 (1993).

69. A. Ruminska, Abhngigkeit zwischen der Entwicklungsphase und dem l- und Azulengehalt als auch dem Ernteertrag der Schafgarbe. Acta Agrobot., 23(1), 53-71 (1970).

70. T. J. Bach, Some new aspects of isoprenoid biosynthesis in plants - A review. Lipids, 30(3), 191-202 (1995).

71. E. Werker, Function of essential oil secreting grandular hairs in aromatic plants of the Lamiaceae. Flav. Fragr. J., 8, 29- 33 (1993).

72. D. McCaskill and R. Croteau, Recent advances in terpenoid biosynthesis: implications for essential oil production. 4 emes Rencontres Internationales, Edit., N. Verlet, Nyons, France, p. 92- 102 (1994).

73. K. Eglseer, Grundlegende Untersuchungen fr die Zchtung pharmazeutisch wertvoller Schafgarben unter besonderer bercksichtigung der proazulene und Sesquiterpenlaktone. PhD Thesis, University Wien (1990).

74. R Cernaj, M. Repcak, K. Tesark and R. Honcariv, Terpenoid compounds from different pans of Achillea collina Becker inflorescences. Biologia Plantarum, 25, 221-224 (1983).

75. G. Kuropka, M. Neugebauer and K.W. Glombitza, Essential oils of Achillea ptarmica. Planta Med., 57, 492-494 (1991).

76. M. Oswiecimska, Variable content of volatile oil and azulenes in herbs milfoil. Part I. variability independent of habitat. Dissertationes Pharmaceuticae, 14, 539-545 (1962).

77. A. S. Shalaby and G. Verzr-Petri, Thin layer and gas- chromatographic studies on the essential oil from Achillea millefolium. Planta Med., 27, 361-366 (1975).

78. E. Tyihk and D. Vgujfalvi, Dunnschichtchromatographische Untersuchung der Proazulene. Planta Med., 15, 269-273 (1967).

79. . N. Zmborin, B. Vadady, and . Hthelyi, Cickafark llomnyok produktivitsa es drogminosge.Lippay-Ormos-Vas Scientific Session, Abstracts, 296-297 (2003).

80. W. D. Loomis and R. Croteau, Biochemistry and physiology of lower terpenoids. In: Recent advances in phytochemistry. Edits., E.C. Runeckless and I. J. Marby, Vol.6., 147-186 Academic Press, New York (1973).

81. A.C. Figueiredo, M.S.S. Pais and J.J.C. Scheffer, Achillea millefolium L. ssp. millefolium (Yarrow): In vitro culture and production of essential oils. In: Biotechnology in agriculture and forestry. Edit. Y. P. S. Bajaj, Vol. 33, p 2-20, Springer-Verlag, Heidelberg (1995).

82. I. Mth, J. Svb, P. Ttnyi and E. Tyihk, Data on prochamazulene content of yarrow in Hungary. Herba Hung., 2(1), 45-57 (1963).

83. A. Ruminska, Morphologische und anzahlmassige Schwankungen der ldrsen wrend der Entwicklung der Blutenkrbchen bei Achillea millefolium. Acta Agrobot., 18, 5-18 (1966).

84. P. Cernaj, B. Galambosi, A. Helemikov, R Mrtonfi and Zs. Szebeni-Galambosi, Effect of spacing and cultivation site on some biological and agricultural properties of Achillea collina Becker. Herba Hung., 30(3), 15-25 (1991).

85. B. Michler, A. Preitschopf, P. Erhard and C. Arnold, Achillea millefolium: Zusammenhnge zwischen Standortfaktoren, Ploidiegrad, Vorkommen von Proazulenen und Gehalt an Chamazulen im atherischen 1. PZ- Wissenschaft, 137(1), 23-29 (1992).

Eva Nemeth*

Corvinus University, Department of Medicinal and Aromatic Plants, H-1118 Budapest, Villnyi str. 29-45, Hungary

* Address for correspondence

1041-2905/05/0005-0501 $6.00/0- 2005 Allured Publishing Corp.

Received: March 2004

Revised: August 2004

Accepted: November 2004

Copyright Allured Publishing Corporation Sep/Oct 2005

Source: Journal of Essential Oil Research : JEOR

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