Secretory structures are common in Asteraceae, where they exhibit a high degree of morphological diversity. The species Verbesina macrophylla, popularly known as assa-peixe, is native to Brazil where it is widely used for medicinal purposes. Despite its potential medical importance, there have been no studies of the anatomy of this species, especially its secretory structures and secreted compounds. This study examined leaves of V. macrophylla with emphasis on secretory structures and secreted secondary metabolites. Development of secretory ducts and the mechanism of secretion production are described for V. macrophylla using ultrastructure, yield and chemical composition of its essential oils. Verbesina macrophylla has a hypostomatic leaf blade with dorsiventral mesophyll and secretory ducts associated with vascular bundles of schizogenous origin. Histochemistry identified the presence of lipids, terpenes, alkaloids and mucopolysaccharides. Ultrastructure suggests that the secretion released into the duct lumen is produced in plastids of transfer cells, parenchymal sheath cells and stored in vacuoles in these cells and duct epithelial cells. The essential oil content was 0.8%, and its major components were germacrene D, germacrene D-4-ol, β-caryophyllene, bicyclogermacrene and α-cadinol. Secretory ducts of V. macrophylla are squizogenous. Substances identified in tissues suggest that both secretions stored in the ducts and in adjacent parenchyma cells are involved in chemical defence. The essential oil is rich in sesquiterpenes, with germacrene D and its derivatives being notable components.

RESUMO Espécies vegetais são capazes de ajustar suas características fi siológicas, anatômicas e ultraestruturais aos fatores ambientais

External factors can interfere with the structure and biological activity of plants. Nevertheless, the susceptibility of plants to specific environmental conditions varies, which raises many questions about the behavior of medicinal plants when grown in urban areas. This study aims to detect possible changes induced by exposure of Eugenia uniflora L. to an urban environment, with emphasis on variation in external and internal leaf structure and differences in the production of its main metabolites. We compared leaves of E. uniflora cultivated in forest and urban sites and analyzed them for structural plasticity and characteristics indicative of stress in the urban environment. The leaves of the urban site revealed necrosis and reddish spots, higher stomatal density, smaller stomata and more numerous crystals and secretory glands, as well as evident storage of starch, lipids, and mucilage. The presence of numerous crystals had a high plasticity index and great potential as anatomical marker for evaluating the effects of the urban environment. Visual symptoms and anatomical changes were efficient at diagnosing stress in E. uniflora, while characteristics of the urban site, such as temperature, heat and pollution, are thought to be responsible for the observed variation and may influence your medicinal characteristic.

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