Micro- and ultramorphological features of the leaf cells of Myrtus communis L. as a parameter for the standardization of medicinal plant syrup are the basis for new herbal remedies

In the context of war, developing and standardizing new medicinal plants, such as Myrtus communis L., can significantly enhance the availability and effectiveness of medicinal products. The micro- and ultramorphological features of the leaf cells of this species could become crucial parameters for their identification and standardization, thereby facilitating the introduction of new, effective medications into practice. The aim of the work is to study the morphological and anatomical structure and determine the general diagnostic microscopic features of leaves and the structure of meristem cells of common myrtle. Materials and methods. Microscopic analysis of temporary leaf preparations of Myrtus communis L. was carried out using a Carl ZEISS “AxioStar Plus” and “Primo Star” microscopes with a photographic attachment for work in both direct and reflected light. The ultrastructure of leaf cells was additionally studied using transmission electron microscopy methods. Ultra-thin sections, 60 nm thick, were obtained on a Reichert Om 43 ultramicrotome. Sections were contrasted with a 1 % solution of uranyl acetate and lead citrate for 2 minutes in each solution at room temperature. Ultrathin sections were studied using a PEM-100-01 electron microscope at an accelerating voltage of 75 kV. Results. The external features of common myrtle (Myrtus communis L.) leaves are described, including their shape, color, and type of veining. Anatomical features of the leaf include the presence of convoluted epidermal cells, anomocytic stomata located on the abaxial surface of the leaf, calcium oxalate crystals and druses, simple hairs on the midvein, and schizolysigenous secretory receptacles. The ultrastructure study of common myrtle leaf cells revealed characteristic structural components of various cell types, including a nucleus with a nucleolus, chloroplasts with plastoglobules and starch grains, a Golgi complex with numerous dictyosomes, endoplasmic reticulum, mitochondria, lysosomes, oil droplets, and myrtle characteristic storage inclusions such as amyloplasts. During electron microscopy, mature secretory receptacles were observed, with visible remnants of cells in the lumen. They are surrounded by cells with a high metabolic rate, as well as senescent cells that appear darker, with low organelle definition and tortuous walls. Conclusions. The leaves of Myrtus communis L. have a hypostomatic leaf type, with the lower epidermis containing a significant number of uniformly arranged stomata of the anomocytic type. Simple unicellular hairs are present only on the central vein. Shared anatomical features with other species in the Myrtaceae family include the presence of druses and prismatic calcium oxalate crystals, along with schizogenous secretory receptacles that produce lipophilic substances. The ultrastructure of meristem cells and cells adjacent to the secretory receptacles in Myrtus communis includes cell membrane, cytoplasm, nucleus, mitochondria, vacuoles, chloroplasts, Golgi complex with numerous dictyosomes, endoplasmic reticulum, lysosomes, oil droplets, and amyloplasts, which are starch-storing inclusions characteristic for the species. Mature secretory receptacles were found, within which cell remnants are surrounded by metabolically active cells and senescent, darker cells with poorly defined organelles and convoluted walls. Recommended parameters for the standardization of Myrtus communis L. medicinal plant material: microscopic indicators include the anomocytic type of stomatal apparatus with hypostomatic placement, simple hairs, the presence of druses and prismatic calcium oxalate crystals, and schizogenous secretory receptacles. Ultramorphological indicators include cell membrane, cytoplasm, nucleus with nucleolus, chloroplasts with plastoglobuli and starch granules, Golgi complex with numerous dictyosomes, endoplasmic reticulum, mitochondria, lysosomes, oil droplets, characteristic storage inclusions (amyloplasts), and the presence of secretory receptacles.