Morfoanatomia, histoquimica e variação sazonal da composição química do óleo essencial de Psidium guineense Swartz (Myrtaceae)

Abstract

Psidium guineense Swartz, commonly known as “araçá-do-campo”, is a fruit bearing shrub native to Brazil, used in folk medicine for the treatment of wound healing and to alleviate throat inflammations, bronchitis, and colds. Its leaves are rich in essential oils with proven pharmacological potential, including antioxidant, anti inflammatory, and antimicrobial properties. The aim of this study was to characterize the morphoanatomy, histochemistry, and variation in chemical composition across the four seasons of the year for the essential oil obtained from the fresh leaves and stems of P. guineense collected in Dourados, MS. The identification of volatile components was carried out using gas chromatography coupled with mass spectrometry (GC-MS). The morphoanatomical and histochemical characterization of the leaves and petioles was performed through light microscopy and scanning electron microscopy. The essential oil yield across the different seasons was highest in the summer (0.341%), with Z-nerolidol being the major compound, ranging from 59.86% to 75.31% across the seasons, with a peak in spring during the species' flowering. Compounds (2Z,6Z)-Farnesol (0.46% 0.65%) and (2Z,6E)-Farnesol (3.18%-4.22%) showed a decrease in the summer, likely due to rainfall and elevated temperatures. Other compounds, such as epi-β-Bisabolol, β Bisabolol, epi-α-Bisabolol, α-Bisabolol, β-Bisabolenol, and α-Bisabolol acetate, were found in higher concentrations during the winter, and in lower concentrations during flowering (spring). 1,8-Cineol (1.12%) exhibited the highest yield in January (summer), a season with significant rainfall. β-Santalene and β-Acorenol were absent during spring. Fruiting may have influenced the variation in β-bisabolene, which was only present in winter and autumn. In the morphoanatomy and histochemistry of the leaves and stems, the essential oil was observed in the secretory glands, primarily in the angular collenchyma, produced by cavity cells. For species characterization, glandular trichomes on the central vein were noted, a feature previously unreported in the genus. Druses and prismatic crystals were also found in the fundamental parenchyma, vascular system of the central vein, and cortex. The crystals consist of calcium oxalate. Thus, it was possible to observe that geographic location, the vegetative state of the species, as well as fruiting and flowering, can directly affect both the chemical composition and yield of P. guineense essential oil. Regarding its anatomy and histochemistry, the species can be identified and differentiated from other species of Psidium.