| Abstract [eng] |
Aim of the work: To determine the effects of phenophases on the quantitative composition of essential oils of Thymus pulegioides L. and on the structures of leaf epidermis related to the accumulation of essential oils. Tasks: To perform a quantitative analysis of Thymus pulegioides essential oils by hydrodistillation method by using Clevenger apparatus and to determine the effects of phenophase on the quantitative composition of T. pulegioides essential oils. To perform analysis of the epidermal structures of T. pulegioides leaves using the imprint method with an optical microscope and to determine the effects of phenophases on the density of T. pulegioides stomata and essential oil glands and the size of essential oil glands. Methodology: T. pulegioides individuals were grown under the same field conditions, without fertilization or watering. The raw material was harvested four times during the different T. pulegioides phenophases: I cutting before flowering, II cutting during full flowering, III cutting after full flowering, IV cutting when the plants had resprouted and flowered for the second time. Air-dried raw material was used for quantitative analysis of essential oils, only leaves and flowers were used, stems were separated from leaves and flowers and were not used for analysis. Essential oils were extracted by hydrodistillation with Clevenger apparatus. Analysis of leaf epidermal structures was performed using the imprint method. During the analysis of leaf epidermal structures, the density of stomata and essential oil glands per mm^2 and size (diameter) of essential oil glands in micrometers, µm, on both sides of leaves were measured. Averages of essential oil amounts, standard errors, average densities of stomata and essential oil glands as well as essential oil glands size, and standard deviations were calculated. Results: To eliminate the influence of different sample mass of raw material, the yield of essential oils in all variants was recalculated as per 100 grams of raw material. Thus, the highest average concentration of essential oil in the raw material was established during the second flowering (1.1475 ml/100 g). The highest average density of stomata on the lower side of leaves was during flowering (468.4 in 1 mm^2), and on the upper side – before the flowering period (36.2 in 1 mm^2). The highest average density of essential oil glands on the lower and upper sides of leaves was during flowering (17.7/mm^2 on the lower side and 17.8 /mm^2 on the upper side). The maximum mean diameter of essential oil glands on the lower and upper sides was before the flowering period (58.4 μm on the lower side and 60.8 μm on the upper side). Conclusions: In phenolic and non-phenolic chemotypes of Thymus pulegioides, the phenophase had no statistically significant effects on the concentration of essential oils per 100 grams of raw material. While it had statistically significant effects on the density of stomata and essential oil glands on both sides of leaves and the diameter of essential oil glands on the lower side of leaves but had no influence on the diameter of the glands on the upper side of leaves. The relationship between the accumulated amounts of essential oils and leaf epidermal structures in Thymus pulegioides is most evident during flowering, when an increased concentration of essential oils and the highest density of essential oil glands on both sides of the leaf and the highest density of stomata on the lower side of the leaf are observed. |
