Thujone is a volatile monoterpene ketone of plant origin which is produced by several plants that are frequently used for flavoring foods and beverages. The use of thujone and thujone-containing plant parts for human consumption is currently regulated by the European Parliament and Council and the European Medicines Agency. The best known neurotoxic effects are connected to the GABA-gated chloride channel, where α-thujone is a modulator roughly two to three times as potent as the β isomer. Based primarily on in vitro experiments, genotoxicity and carcinogenic properties of thujones have also been detected in parallel with antimutagenic and immune-modulatory effects. Some of the controversial effects seem to be strongly dose-dependent. Data on antidiabetic and antimicrobial activities of thujones may show new ways to use them. This review also describes the main steps of the biosynthetic route of thujones and their occurrence in the plant kingdom. The accumulation of these compounds seems to be more abundant in some plant families (e.g. Asteraceae or Cupressaceae) than in others. Four species (Artemisia absinthium, Salvia officinalis, Tanacetum vulgare, Thuja occidentalis), characterised by a large intraspecific chemical variability, have been evaluated in detail from chemotaxonomical aspects. Experimental results show that the phenotypic manifestation and quantity of thujones in the essential oils depend on the plant organ and its developmental phase. Besides, weather conditions and growth habitat might also influence the ratios, as well as the possibly unique responses of the individual species. Unfortunately, comparison and an exact evaluation of the references is hampered by very diverse methods of treatment and analysis; sometimes reliability itself seems questionable. In order to optimise the safe use of thujone-containing preparations, it would be necessary to do further systematic studies from the plant biological, toxicological and pharmaco-kinetic points of view.

Two experiments (in Petri dishes and in soil) were conducted to investigate the effects of osmopriming on seed germination and the early seedling characteristics of caraway (Carum carvi L. var. annua). The priming treatments in the Petri dish experiment were: polyethylene glycol (5%, 10% and 20%), KNO₃ (0.5%, 1% and 2%) and KCL (1%, 2% and 4%) with three different soaking times (12, 24 and 36 h) along with control (non-primed seeds). Only polyethylene glycol and H₂O were applied in the cell tray experiment, which were then compared with the non-primed seeds. In the Petri dish experiment, all three priming reagents significantly enhanced seedling length, with the most effective treatments being 5% PEG, 2% KNO₃ and 1% KCL for 12 h. The plumule dry weights were also increased significantly after PEG (20% for 36 h), KNO₃ (2% for 24 and 36 h) and KCL (1% for 12 h) treatments in comparison with the control. In the soil experiment, osmopriming with PEG significantly improved the germination rate (GR) and percentage, the plumule dry and fresh weights and the plumule length of caraway seedlings when compared with the control. A 23% higher germination percentage was recorded for the seeds treated with 5% PEG for 24 h as compared with the non-primed seeds. The PEG-primed seeds produced significantly longer seedlings when treated with 5% PEG for 24 h. All of the applied PEG treatments significantly enhanced the plumule fresh and dry weights, with the best outcomes being after 5% PEG (24 h) and 10% PEG (36 h) treatments, respectively. The 12-h hydro-priming also significantly enhanced all of the studied germination parameters when compared to the control. The results of the presented experiments show the significant positive effects of seed priming on caraway germination and how early seedling performance can easily be adopted by producers.

Stimulating the production of secondary metabolites by elicitation seems to be an accepted tool in several in vitro cultures. In vivo application of chemical elicitation is, however, much less frequently discussed. The paper summarizes the experimental findings on the effects of jasmonic acid, methyl-jasmonate (MeJa) and salicylic acid (SA) treatments on medicinal and aromatic plants. Growth behaviour, yield, stress responses, essential oil (EO) and phenolic compounds are discussed. Exogenous application of MeJa or SA mostly by foliar spraying in concentrations between 10⁻⁴ and 4 mM, induced various changes in the plants. In most cases, the elicitation enhanced the volatile accumulation, although the opposite reaction was observed too. Numerous in vivo trials also demonstrated an altered EO composition. Positive effects of treatments on the concentration of phenolic type compounds were described, while in some cases the components exhibited contradictory behavior or no significant changes. Unfortunately, phenolic composition was rarely determined. There is evidence for the dose dependency of the reactions to both elicitors, but systematic studies on this issue are missing. Some results indicate that lower concentrations in replication may be at least as effective as higher ones. Changes in secondary metabolite accumulation may be induced by the elicitors directly or through other physiological processes. The in vivo results should be considered in the complex system of plant ontogenesis, environmental conditions, timing of the treatment, type of the elicitor and concentration. Research results indicate a promising aspect of chemical elicitation in vivo, but further well-designed studies are needed for the individual species.

Salicylic acid (SA) and methyl jasmonate (MeJa) are prominent phytohormones that are involved in stress reactions. Both compounds may influence the biosynthesis of secondary compounds; however, scientific experiments in vivo are rare and contradictive. This paper reports on a study on the elicitation of volatiles and total phenolics (TPC) by MeJa and SA. The subjects were four Lamiaceae species studied in open field conditions in Budapest (Hungary). According to the results, both elicitors provoked specific responses in each plant species depending on the dosage applied and the parameter studied; 2 mM of SA stimulated essential oil (EO) accumulation in marjoram and peppermint, while in hyssop 0.1 mM was optimal. MeJa proved to be effective only in marjoram and in basil. In marjoram, cis-sabinene hydrate was decreased and in hyssop, isopinocamphone was increased by both dosages of SA. In peppermint, pulegone content was reduced by 2 mM SA, but no significant change of the major components of basil EO was detected. SA was successful in increasing TPC and antioxidant activity (AC) in three of the experimental species, but not in hyssop. In marjoram, only 0.1 mM induced TPC and eventually AC, while in peppermint and basil both dosages of SA were effective. Optimalisation of the treatments is suggested in further in vivo experiments.

The reactions of Majorana hortensis, Melissa officinalis, Mentha piperita and Thymus vulgaris were investigated in controlled conditions to compare their responses on drought stress concerning yield, essential oil (EO) content and composition. Biomass and essential oil concentration were significantly decreased in each species similarly, if they were grown at 40% level of soil water capacity (SWC) compared to the ones growing at 70% SWC. The largest changes were detected in lemon balm (4.47-fold difference in biomass, 2.78-fold difference in EO content) while the response of marjoram was the modest one (1.95-fold in biomass, 1.21-fold in EO content). We found species specific quantitative modifications in the EO composition. The ratio of terpinene-type components increased in the EO of both thyme and marjoram to the expense of their characteristic compounds thymol, carvacrol and sabinyl compounds, respectively. The composition of lemon balm and peppermint, however, did not show considerable changes.

The goal of this study was to clarify the role of capsule size and morphology in the alkaloid yield of poppy. In 2023, two industrial varieties from large-scale cultivation were investigated. Three classes of capsule size (large, medium, and small) and four organelles (wall, placenta, disc, and thalamus) of the seedless capsule were studied for their mass proportions and alkaloid contents. In ‘Meara’, large capsules had 41% lower total alkaloid levels than smaller ones. In ‘Morgana’, there was no difference in total alkaloids between size groups, but large capsules had higher contents of codeine and thebaine. Among the four organelles, the wall represented the largest mass in both varieties (60–67%), while the disc and the thalamus gave the lowest proportions (below 9%). In the variety ’Meara’, the highest alkaloid contents appeared in the wall (2.69% d.w.), followed by the placenta, and the other two parts. ‘Morgana’ accumulated the highest alkaloid content (3.72% d.w.) in the placenta. Morphine follows the trend of the total content, while codeine and thebaine may differ. Accurate information on the accumulation of alkaloids in the generative organs may contribute to increasing effectiveness in target-oriented breeding and optimization of cultivation with an appropriate choice of variety.