Secretory Structures inCasearia sylvestrisSw. (Salicaceae): Diversity, Mechanisms of Secretion, and Exudate Complexity

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Premise of research. Casearia sylvestris (Salicaceae) is widely used in traditional medicine and possesses various types of secretory structures, but the mechanisms and compartments involved in the secretory processes have not been elucidated. This study aims to describe the chemical nature of the secretions produced by all secretory structures of C. sylvestris leaves and to identify the compartments and mechanisms of synthesis, storage, and release of secretion.Methodology. Shoot samples were collected and analyzed using standard techniques for light microscopy and for scanning and transmission electron microscopy. Histochemical tests were performed to identify the main classes of exudate compounds.Pivotal results. The subcellular compartments involved in the secretory process of the taniferous idioblasts, cavities, ducts, and colleters were identified, with all organelles being consistent with the chemical nature of secretion. In the colleters, plastids with osmiophilic compounds are related to the production of oil, while dictyosomes are associated with syntheses of polysaccharide secretion. The smooth endoplasmic reticulum, periplastidial reticulum, and plastids present in the secretory epithelium of the cavities and ducts produce the oleoresin, while dictyosomes are involved with hydrophilic secretion.Conclusions. Ultrastructure variation among the organelles of the four types of secretory structures studied, as well as the chemical complexity of exudates produced by them, revealed particularities that enabled the description of models for the secretory mechanism of each. Novelties that reveal the mechanisms involved in the release of secretion through the cell wall are presented.

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