Sites of secretion of bioactive compounds in leaves of Dracocephalum moldavica L.: anatomical, histochemical, and essential oil study

Marta Dmitruk,Ernest Stawiarz,Aneta Sulborska,Elżbieta Weryszko-Chmielewska,Beata Żuraw

doi:10.1007/s40415-019-00559-6

Marta Dmitruk, Ernest Stawiarz + Show 3 more

Open Access

https://doi.org/10.1007/s40415-019-00559-6

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Abstract

Dracocephalum moldavica L. is an aromatic plant emitting intense lemon scent. The aboveground parts of the plants constitute raw material for medicine and food industry. In contrast to the comprehensively investigated trichomes, there are only few studies of the histochemical characteristics of the leaves of essential oil-bearing plants from the family Lamiaceae. The present study shows the micromorphology, anatomy, and histochemistry of the leaves of the analysed species. The research aimed to determine the location of essential oil and other specialised metabolites in leaf tissues. The investigations of fresh and fixed material were carried out with the use of light, fluorescence, and scanning electron microscopy. Additionally, the content and composition of essential oil in the leaves were determined with the GC/MS method. The leaf epidermis had non-glandular unbranched trichomes and three types of glandular trichomes: peltate as well as long and short capitate trichomes. The results of the histochemical assays showed positive reactions to lipids and to some secondary compounds such as essential oil, terpenes, phenolic compounds, and flavonoids in all types of the glandular and non-glandular trichomes. The same compounds were found in the epidermis cells of the leaves. The results of the present study indicate that the intense smell of the leaves is associated with emission of essential oil not only by the glandular and non-glandular trichomes but also by the leaf epidermis cells. The main components in the essential oil (0.10%) include geranial, neral, geraniol, nerol, and trans-myrtanol acetate. Since D. moldavica has been used as an adulterant of Melissa officinalis L., the anatomical traits of leaves and the essential oil composition in both species were compared in the study.

Highlights

The genus Dracocephalum represents the family Lamiaceae (Labiatae) and comprises approximately 40 species, a majority of which originate from the mountains of Central Asia, mainly from the Altai (Hegi 1965; Brickell 1999)
Leaf morphology – Stem leaves There are two leaves growing from each node below the inflorescence on the Dracocephalum moldavica stem (Fig. 1a)
We have demonstrated the presence of flavonoids in the some leaf epidermis cells, and in the basal cells of trichomes, which is indicated by the yellow–green secondary fluorescence of these cells after the treatment with

Summary

Introduction

The genus Dracocephalum represents the family Lamiaceae (Labiatae) and comprises approximately 40 species, a majority of which originate from the mountains of Central Asia, mainly from the Altai (Hegi 1965; Brickell 1999). These are mostly perennials and, more rarely, annual plants or subshrubs. Dracocephalum moldavica L. is naturalised in eastern and central Europe (Dastmalchi et al 2007). In Poland, it is a cultivated species and can be found in natural habitats as a “runaway” from gardens (Rutkowski 2006). The species was introduced into the gardens of Europe as. D. moldavica (Moldavian dragonhead) comprises herbaceous, annual, strongly aromatic plants with an agreeable lemon scent. The large flowers with a corolla length of 20–25 mm are usually purple–blue and, less frequently, light blue or white (Hegi 1965; Dmitruk and Weryszko-Chmielewska 2010; Dmitruk et al 2018)

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