Geraniol and Carvacrol in Essential Oil Bearing Thymus pulegioides: Distribution in Natural Habitats and Phytotoxic Effect.

Phenolic and non-phenolic chemotypes of Thymus pulegioides L. are common in Europe. Essential oils of these chemotypes, as various compositions of allelochemicals, can have different phytotoxic effects on neighboring plants in natural habitats. The aim of this study was to establish the distribution of carvacrol and geraniol in T. pulegioides, growing wild in Lithuania, and compare phytotoxity of essential oils of carvacrol and geraniol chemotypes on selected plant species. In investigating 131 T. pulegioides habitats, essential oils were isolated by hydrodistillation and analyzed by GC-FID and GC-MS. Phytotoxity of essential oils extracted from carvacrol and geraniol chemotypes transmitted through water and air to selected plants was determined under laboratory conditions. Pharmacologically valuable Hypericum perforatum L. and the important forage grass Phleum pratense L. were respectively selected for experimentation from among 35 medicinal plants and 10 feed Poaceae species, growing in T. pulegioides habitats. Field results showed that carvacrol is common throughout Lithuania's territory, whereas the geraniol is predominantly located under the continental climatic conditions of the eastern region of the country. In the laboratory experiment, it was established that there was stronger inhibition of P. pratense seed germination by the essential oil of the geraniol chemotype than the carvacrol chemotype. None of the H. perforatum seeds germinated after exposure to the essential oil of the geraniol chemotype. In general, this study builds on previous studies by providing further evidence that different T. pulegioides chemotypes have contrasting phytotoxic effects on neighboring plants within their natural habitats.

α-Terpinyl Acetate: Occurrence in Essential Oils Bearing Thymus pulegioides, Phytotoxicity, and Antimicrobial Effects.

The aim of this study was to evaluate occurrence of T. pulegioides α-terpinyl acetate chemotype, as source of natural origin α-terpinyl acetate, to determine its phytotoxic and antimicrobial features. Were investigated 131 T. pulegioides habitats. Essential oils were isolated by hydrodistillation and analyzed by GC-FID and GC-MS. Phytotoxic effect of essential oil of this chemotype on monocotyledons and dicotyledons through water and air was carried out in laboratory conditions; the broth microdilution method was used to screen essential oil effect against human pathogenic microorganisms. Results showed that α-terpinyl acetate was very rare compound in essential oil of T. pulegioides: it was found only in 35% of investigated T. pulegioides habitats. α-Terpinyl acetate (in essential oil and pure) demonstrated different behavior on investigated plants. Phytotoxic effect of α-terpinyl acetate was stronger on investigated monocotyledons than on dicotyledons. α-Terpinyl acetate essential oil inhibited seeds germination and radicles growth for high economic productivity forage grass monocotyledon Poa pratensis, but stimulated seed germination for high economic productive forage legume dicotyledon Trifolium pretense. α-Terpinyl acetate essential oil showed high antimicrobial effect against fungi and dermatophytes but lower effect against bacteria and Candida yeasts. Therefore, T. pulegioides α-terpinyl acetate chemotype could be a potential compound for developing preventive measures or/and drugs for mycosis.

Chemical Composition of Essential Oils and Local Knowledge of Myrica gale in Lithuania.

Myrica gale L. (Myricaceae) is an essential oil-bearing plant that is rare in Lithuania and naturally grows only in the western part of the country. The aim of this study was to analyze the composition of essential oils of Myrica gale in different habitats in Lithuania and in different parts of the plant, as well as evaluate the local knowledge about M. gale as a medicinal and aromatic plant. Samples of fruits and leaves (from one and three M. gale populations, respectively) were studied separately. Essential oils were isolated from dried fruits and leaves by hydrodistillation and analyzed by GC/FID and GC/MS methods. Results showed that M. gale fruits accumulated 4.03 ± 2.13% essential oils, meanwhile leaves-up to 19 times less. A total of 85 compounds were identified in the essential oils of the M. gale. Monoterpene hydrocarbons accounted for about half of the total essential oil content; meanwhile, either monoterpene hydrocarbons or sesquiterpene hydrocarbons (depending on habitat) dominated in leaves. The main compounds (depending on habitat) in essential oils of fruits and leaves were α-pinene, 1,8-cineole, limonene, δ-cadinene, and (E)-nerolidol. The high variation in the composition of M. gale essential oils suggests the presence of different chemotypes within the studied habitats of this plant. Evaluation of local knowledge of M. gale through the survey of 74 residents of 15 villages in western Lithuania showed that only 7% of respondents knew this plant. Poor knowledge of M. gale could be related to the narrow range of the natural species' distribution in Lithuania.

Impact of Edaphic and Climatic Factors on Thymus pulegioides Essential Oil Composition and Potential Prevalence of Chemotypes.

Intraspecific chemical polymorphism is characteristic of essential oil bearing Thymus pulegioides (Lamiaceae). Soil chemical composition and climatic conditions can influence not only quantitative and qualitative composition of essential oils, but also on prevalence of different chemotypes in space. The purpose of study was to determine the impact of edaphic and climatic factors on T. pulegioides essential oil composition and potential chemotypes prevalence. It were investigated 131 habitats of T. pulegioides in all ten climatic sub-districts of Lithuania. Essential oils were isolated by hydrodistillation and analysed by GC-FID and GC-MS. The content of humus was estimated by oxidation method, the content of mobile potassium (K2O) and mobile phosphorus (P2O5)-flame photometry using 0.2 M HCl solution, the soil pH-electrometrically and 15 elements of soil-by energy-dispersive X-ray fluorescence. The meteorological data (temperature, rainfall, photosynthetically active solar radiation and sunshine duration) were obtained from the meteorological bulletins. Results showed that humus in soil positively, manganese and cobalt-negatively influenced on the essential oil accumulation in T. pulegioides. Carvacrol was the most common compound in the essential oil of T. pulegioides; higher amounts of sulphur and mobile phosphorus, lower amounts of sodium in soil, higher rainfall in blooming period are favourable for this compound and for potential prevalence of carvacrol chemotype. Geraniol was frequent in the eastern and the central part of Lithuania, where the temperature in vegetation season is higher, and in soils characterised by higher and lower amounts of sodium and chlorine, respectively. Thymol, linalool and α-terpinyl acetate were rare. Edaphic and climatic conditions can differently influence on essential oil yield and chemical composition of species as well as on potential prevalence of different chemotypes of same species in space.

Effects of meteorological conditions and plant growth stage on the accumulation of carvacrol and its precursors in Thymus pulegioides.

The effects of meteorological conditions (temperature, rainfall, photosynthetically active solar radiation (PAR) and sunshine duration) and plant growth stages on the quantitative composition of a secondary metabolite - essential oil and its main compounds, in the carvacrol chemotype of Thymus pulegioides L. (Lamiaceae) cultivated in open ground were studied under the same micro-edaphoclimatic environmental conditions for six years. The essential oil was isolated by hydrodistillation, the analysis of monoterpenic phenol carvacrol and the biogenetic precursors (monoterpene hydrocarbons p-cymene and γ-terpinene) were carried out annually using GC-FID and GC-MS. In the carvacrol chemotype investigated in this study, the yield of essential oil varied from 0.72% to 0.98% (CV = 12%) at full flowering stage. Regression analysis showed a significant negative relationship between the amount of essential oil and both temperature and rainfall during T. pulegioides flowering (July) and the period from April (beginning of vegetation) to July, but a strong positive relationship with photosynthetically active solar radiation during April-July (beta = 0.658, p < 0.05). The percentage of carvacrol, p-cymene and γ-terpinene ranged between 16.88 and 29.29% (CV = 18%), 5.54-11.33% (CV = 23%) and 20.60-24.43% (CV = 6%) respectively. Regression analysis showed the significant positive relationship between the percentage of carvacrol and sunshine duration at the flowering stage (in July) (beta = 0.699, p < 0.05); while the negative relationship was established between the percentages of precursors of carvacrol and photosynthetically active solar radiation and sunshine duration. The accumulation of p-cymene, the percentage of which varied most strongly from all investigated chemical compounds, showed significant positive relationships with temperature and rainfall during the period April-July and temperature in July (beta = 0.617, beta = 0.439 and beta = 0.429 respectively, p < 0.05). The analysis of plant growth stages showed that the highest amount of essential oil in carvacrol chemotype of T. pulegioides accumulated at ripening/seed maturity stage. The percentage of carvacrol increased gradually from the stem elongation to the post-flowering/seed maturity stage, overtaking the full flowering stage by 22%. The highest carvacrol content in the T. pulegioides carvacrol chemotype coincided with the highest oil yield during the fruiting stage. The amount of essential oil was also measured at the second full flowering stage, because after cutting the aerial part of the plant at the full flowering stage T. pulegioides often bloom for a second time: the carvacrol chemotype accumulated by 21% lower yield of essential oil at this stage compared to the first flowering, however, only traces of carvacrol and its precursors were found at the second full flowering stage.