Abstract
(1) Background: Centaurea cyanus L. is a medicinal plant whose flowers are widely used in herbal medicine. The aim of the study was to localise flower tissues that are responsible for the production of secretory products in petals and to analyse the volatile compounds. The volatile compounds of the flowers of this species have not been investigated to date. (2) Methods: Light, fluorescence, scanning and transmission electron microscopy techniques were used in the study. Lipophilic compounds were localised in the tissues using histochemical assays. Volatile compounds were determined with the use of solid phase microextraction (SPME) and gas chromatography-mass spectrometry (GC-MS). (3) Results: The study showed production of secretion in the petal parenchyma, whose ultrastructure has features of a secretory tissue. The lipophilic secretion was localised in the cells and intercellular spaces of the parenchyma and in the walls and surface of epidermal cells, where it accumulated after release through cuticle microchannels. Sesquiterpenes were found to constitute the main group of volatile compounds, with the highest content of β-caryophyllene (26.17%) and α-humulene (9.77%). (4) Conclusions: Given the presence of some volatile components that are often found in resins (caryophyllene, delta-cadinene) and the abundant secretion residues on the epidermal surface, we suppose that the C. cyanus secretion released by the flowers is a resinaceous mixture (oleoresin), which is frequently found in plants, as shown by literature data. This secretion may play an important role in the therapeutic effects of C. cyanus flowers.
Highlights
Plants emit different volatile organic compounds from their aerial and underground parts [1]
Sesquiterpenes were found to constitute the main group of volatile compounds, with the highest content of β-caryophyllene (26.17%) and α-humulene (9.77%). (4) Conclusions: Given the presence of some volatile components that are often found in resins and the abundant secretion residues on the epidermal surface, we suppose that the C. cyanus secretion released by the flowers is a resinaceous mixture, which is frequently found in plants, as shown by literature data
The length of the funnel-shaped ray florets consisting of fused petals (Figure 1B) was 14–18 mm, and their widest diameter was in the range of 9–14 mm
Summary
Plants emit different volatile organic compounds from their aerial and underground parts [1]. Most often they are produced by leaves and flowers of aromatic plants [2]. Volatile organic compounds serve various functions in flowers: attraction of pollinators or defence against herbivores and pathogens [3]. There are hydrocarbon and derived mono-and sesquiterpenes, aliphatic and olefinic C6–C12 non-terpene aldehydes, alcohols, ketones, esters, and acids, along with several aromatic compounds. Among these compounds, mainly terpenes are responsible for the medicinal, culinary, and fragrant uses of aromatic plants [7]. The non-volatile residue is mainly composed of flavonoids, coumarins, diterpenoids, sterols, and fatty acids [8]
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