Abstract
Clinopodium pulegium (Rochel) Bräuchler (Lamiaceae) is an endangered species endemic to the Southern Carpathians. It is characterized by the production of high amounts of essential oils, which emit volatile organic compounds (VOCs) that have an essential role in biotic and abiotic stress responses and in plant–plant and plant–insect interactions. The present study was initiated to phytochemically examine the influence of different carbon sources in the nutrition medium on VOC emissions of micropropagated C. pulegium plants, using gas chromatography–mass spectrometry analysis of headspace VOCs. The volatile profiles were subjected to multivariate analysis with respect to the presence, concentration and type of carbon source in the nutrient medium. In addition, the effect of different carbohydrates on the density and size of the leaf glandular trichomes, the main structures involved in the emission of VOCs, was determined. A total of 19 VOCs, primarily belonging to mono- and sesquiterpenes previously described in plants, were tentatively identified. Six VOCs were produced at levels higher than 2% of the total VOC emission, dominated by pulegone, ß-pinene and menthone. Inclusion of the carbohydrates in the culture media affected the production of the main leaf trichome-associated volatile allelochemicals although the qualitative composition of the volatiles changed only slightly. Multivariate analysis showed that the concentration, rather than the carbohydrate type, influenced the VOC profile.
Highlights
IntroductionMany of the species belonging to the Lamiaceae family are considered aromatic and medicinal plants due to the presence of glandular trichomes that are the main sites for the synthesis of natural bioactive compounds
The growth and multiplication of C. pulegium was obtained on control medium, devoid of carbohydrates, where only about 50% of nodal explants produced 1–2 shortened shoots
The multiplication rate on fructose-supplemented media progressively decreased with an increase of fructose concentration in the culture medium, with a drastic decrease in explant responsiveness observed for 5% fructose (Figure 1A)
Summary
Many of the species belonging to the Lamiaceae family are considered aromatic and medicinal plants due to the presence of glandular trichomes that are the main sites for the synthesis of natural bioactive compounds. These bioactive compounds play a crucial role in mediating the plant–environment interactions, often rendering a commercial value to the plants that produce them [1]. (Lamiaceae) comprises 135 perennial herbs [2], including taxa that were recently transferred from the polyphyletic genus Micromeria sect. Pseudomelissa based on molecular and morphological/anatomical evidence [3].
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