Myrtus communis L. subsp. communis

Myrtus communis L. subsp. communis: History

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Subjects: Plant Sciences

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Myrtus communis subsp. communis is an evergreen shrub or a small tree, growing spontaneously throughout the Mediterranean basin. The stem is branched from the basal portion and the bark is brownish or reddish in color. The leaves are simple, opposite, sessile or sub-sessile, glossy, and dark green in color, lanceolate or ovoid-elliptical in shape with entire or slightly revolute margins and acute apices; they are very aromatic due to the presence of numerous secretory cavities. The flowers, white in color with yellowish streaks, are solitary or coupled at the leaf axil. The fruits are ellipsoidal or subspherical berries, red-violet or blackish in color at maturity, with persistent calyx residues.

myrtle
botanic gardens
secretory cavities
essential oils
α-pinene
1
8-cineole and linalool chemotype
light microscopy
GC-MS
Open science

1. Introduction

Myrtle has a consolidated ethnobotanical tradition and is used in different parts of the world, against colds and coughs [4], for self-medication of digestive problems, for skin disorders [5], for the treatment of obesity, hypercholesterolemia, and diabetes [6,7]. The essential oils (EOs), obtained from shoots, leaves and sometimes flowers and berries, are used eminently in perfumery. The berries are also employed in the production of bitters and famous liquors. Due to its broad use in folk medicine, myrtle has been widely investigated, especially with regards to the EO composition [8,9,10,11,12,13,14]. In Italy, previous studies were focused on plants from Sardinia, Sicily, Campania, and Liguria regions [11,12,15,16,17,18]. Concerning literature data on the micromorphology, previous investigations were focused on the structure and ontogeny of the secretory cavities of leaves and flowers by means of both light and electronic microscopy [19,20,21,22].

2. Micromorphological Investigation

The micromorphological survey showed the occurrence of secretory cavities both in the leaves and in the shoots. In the leaves these structures were variously distributed: in the palisade parenchyma, where they are located immediately below the adaxial epidermis; in the spongy parenchyma, and especially in the transition region with the palisade mesophyll or adjacent to the abaxial epidermis (Figure 2a,b). In the shoots, the cavities had a reduced diameter and generally occurred in the cortical parenchyma.

Figure 2. (a,b) Cross section of Myrtus communis subsp. communis leaf colorless (a) and stained with Toluidine blue dye, (b); (c) Detail of a leaf secretory cavity, colorless; (d) Detail of a shoot secretory cavity; (e–g) Histochemistry of secretory cavities: Nadi reagent (e), Fluoral Yellow-088 (f), AlCl₃ (g). Scale bars = 100 µm (a,b); 25 µm (c,d,g); 50 µm (e,f).

The secretory cavities, regardless of the distribution pattern, were globose-spheroidal in shape and had a diameter ranging from 10 to 50 µm (Figure 2c). The cavities displayed a 1-layered epithelium consisting of secreting cells that released the secreted material inside the cavity (Figure 2d). The cavities generally appeared empty, but sometimes the accumulation of colorless or pale-yellow material was observed; the secreted material consisted of small, densely packed droplets or of large clusters which filled the entire volume of the cavity. These results are in accordance with those reported in the literature [19,22].

The histochemical tests revealed consistent results between the cavities of leaves and shoots (Figure 2e–g). All the dyes specific for lipophilic substances gave positive responses, with special reference to the NADI reagent indicating the presence of terpenes (Figure 2e,f). Furthermore, the production of flavonoids was for the first time highlighted in the cavities of M. communis subsp. communis following the treatment with AlCl₃ (Figure 2g), while the tests specific for polysaccharides and proteins gave negative results.

This entry is adapted from the peer-reviewed paper 10.3390/plants11060754

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