Morphological and histochemical characterization of the secretory sites of bioactive compounds in leaves of Lantana camara L. (Verbenaceae)

Abstract

Lantana camara L. is a species of Verbenaceae known for its aromatic and medicinal properties. Compounds extracted from its leaves are used to treat infections of the respiratory tract and have demonstrated antimicrobial potential and repellent action to Aedes mosquitoes. Our aim was to identify and characterize the main production sites of the biologically active substances in the leaf blades of L. camara. Leaf samples were collected from plants living in the Brazilian Cerrado and processed according to standard techniques in plant anatomy and histochemistry as well as scanning and transmission electron microscopy. Six morphotypes of glandular trichomes (I–VI) were identified; they differ in shape and size, number of constituent cells, subcellular aspects, and form of accumulation, as well as release and composition of the secretion. Idioblasts producing hydrophilic and lipophilic substances were observed in the mesophyll and may be associated with protection of the plant against herbivores and pathogens and maintenance of the water potential of leaf tissues, complementing the action of glandular trichomes. Our results contribute to the understanding and knowledge of the sites responsible for the production of substances with ecological and medicinal value in Verbenaceae species, and may provide a foundation for future studies in different areas of science focusing on the manipulation of this production.

Morphology and histochemistry of glandular trichomes in Hyptis villosa Pohl ex Benth. (Lamiaceae) and differential labeling of cytoskeletal elements

“…Polysaccharides are important in the maintenance of the hydric potential of the cells protecting the organs against desiccation (Ascensão et al 1999;Werker 2000), important role in environment with low humidity as in the Brazilian Cerrado. Phenolic compounds are also important in the defense against herbivores and pathogens and in the protection of the plants against high irradiance, like that in the Cerrado, that could cause photoinhibition and damage to the cell machinery (Liakoura et al 1997;Tozin et al 2015a;Silva et al 2016). Total lipids and terpenes were abundantly stained by the histochemical tests in the morphotype I, mainly in the head cells.…”

“…Some secretion can accumulate as paramural bodies in the periplasmic space before to reach the outside of the cells. The presence of voluminous electron-dense bodies inside plastids as observed in the head, neck and stalk cells of this glandular morphotypes is a common feature to cells producing and accumulating proteins (Fahn 1979;Evert 2006;Silva et al 2016); in addition, the occurrence of plastids with starch grains of different sizes in the stalk cells suggest the involvement of these cells in providing energy to the production of secretion by degradation of the carbohydrates (Nepi et al 1996;Paiva & Machado 2008;Silva et al 2016). The occurrence of a pedestal elevating the apical portion of the trichome is remarkable in the morphotype III; the occurrence of thick walls and reduced cytoplasm in the pedestal cell indicates its fundamental role in supporting the apical portion of the trichome (Silva et al 2016).…”

“…The widespread presence of plasmodesmata in morphotypes I, II and III connecting the cells of the trichomes among themselves and to the neighboring cells suggests the symplastic passage of substances from the lower cells toward the head cells of trichomes (Ascensão et al 1999;Evert 2006;Argyropoulou et al 2010;Silva et al 2016). These substances may represent precursors of the secretion that will be synthetized in the head cells (Ascensão et al 1999;Tozin et al 2015a;Silva et al 2016).…”

“…Substances of diff erent chemical categories can be produced by glandular trichomes, and their subcellular features vary according to the substances produced and the form of release of the secretion (Ascensão et al 1995;Ascensão & Pais 1998;Appezzato-da-Glória et al 2012;Naidoo et al 2012;Tozin et al 2015a;Silva et al 2016).…”

“…Th e subcellular features of glandular trichomes have been exhaustively described to several species from diff erent families (Ascensão & Pais 1998;Sacchetti et al 1999;Argyropoulou et al 2010;Papini et al 2010;Paiva & Martins 2011;Appezzato-da-Glória et al 2012;Naidoo et al 2012;Amrehn et al 2014;Tozin et al 2015a;Silva et al 2016 and references therein); however, some important aspects, such as the involvement of the cytoskeletal elements in such secretory process remains poorly studied. It has been demonstrated that movement of oil droplets in the Morphology and histochemistry of glandular trichomes in Hyptis villosa Pohl ex Benth.…”