Buckwheat leaves and young parts of the plant are consumed in some countries as a vegetable. Green flour, obtained by milling of the dried plants, is used as a natural food colorant. The distribution of vitamin E, squalene, epicatechin, and rutin (as the most important antioxidants) within buckwheat plants, as well as changes of their content within leaves during the growing season, were determined by GC-MS and HPLC analyses. alpha-Tocopherol was found as the main component of vitamin E in all parts of the plant; epicatechin and squalene were also detected. For the use of buckwheat as an antioxidant source in the human diet, the most suitable part of the plants seems to be the leaves and the flowers at the stage of full flowering due to the considerable amounts of rutin and epicatechin. alpha-Tocopherol content correlates positively with temperature, drought, and duration of solar radiation. Certain differences appear among varieties of buckwheat, especially in their squalene and rutin contents.

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Root exudates of the common buckwheat, especially phenolic compounds, were studied. Their contents, both in the soil during the growing season and in agar medium during germination, were determined by HPLC and GC-MS. The allelopathic activity of the soil from a buckwheat stand was evaluated, as well. Palmitic acid, squalene, epicatechin, vitexin, a gallic acid derivative, and a quercetin derivative were the main compounds of the agar medium. In the soil, palmitic acid methyl ester, vanillic acid, rutin, a gallic acid derivative, and a 4-hydroxyacetophenone derivative were identified. The effects of vitexin, squalene, epicatechin, 4-hydroxyacetophenone, and vanillic and gallic acids were tested on eight plant species. Inhibitive effects were observed in the cases of 4-hydroxyacetophenone and vanillic and gallic acids. Comparisons of the identified compounds and inhibitive effects of soil extracts indicated that palmitic acid and the gallic acid derivative probably have an important function in the allelopathic root response of buckwheat.

Oil samples from four chemotypes of Thymus vulgaris were tested for mosquitocidal activity. Oil compounds were analyzed by gas chromatography-mass spectrometry (GC-MS). The different compositions of the oils varied in their biological activity as well. Larvicidal efficiency was determined for the most significant oil thymol type (T), namely the lowest doses LD(50) 32.9 and 14.2 mg/l for the third and fourth instars, respectively. The oils also showed very good efficiency with respect to mortality and to the percentage of adult emergence upon short-term exposure in water treated by lethal doses of individual oils. Although the larvae were left in treated water for only 5 h, mortality corresponding to LD(50) was determined after 24 h, i.e., between 49% and 63%. Furthermore, mortality increased significantly in relation to time of exposure, and total mortality of the larvae at the end of their development was about 90%. Such significant mortality was also naturally reflected in the total emergence of adults. In the control sample, there was 77% adult emergence from the larvae, whereas in oils, there was only from 5.3% to 16% emergence. The greatest fumigate efficiency was found for T and linalool chemotypes, with an LC(50) for 24 h of exposure being 1.1 and 1.8 mg/l, respectively. Essence T was also most efficient in the tarsal test, with LD(50) of 44 microg/cm(2) and LD(90) of 63 microg/cm(2). High antioviposition efficiency was found in all tested oils.

The quality of medical plants used for the production of galenics or pharmacologically useful compounds is usually assessed by the content of biologically active compounds. Because most of these plants are grown in fields, this study focused on stimulation of active compounds by in vivo elicitation. Foliar application of elicitors on the immunostimulating medical plant purple coneflower ( Echinacea purpurea L. Moench.) grown on soil was used to increase the content of biologically active phenolics. Natural plant stress mediators and their derivatives (acetylsalicylic acid, salicylic acid, and methyl salicylate) as well as newly introduced biocompatible metal elicitor [titanium(IV) ascorbate] were chosen as active components of foliar sprays. A tremendous increase of phenolics (up to 10 times compared to control) and stimulation of the biomass yield were achieved. Tuning of organ specificity by modulation of the concentration of elicitor was also observed. This methodology represents a convenient alternative to cell suspension or hydroponic cultures being applicable in wide agricultural practice.