Ontogenesis, histochemistry, and seasonal and luminous environmental characterization of secretory cavities in leaves of Myrcia splendens (Myrtaceae)

Secretory cavities produce compounds that protect plants from herbivory and pathogenic microorganisms. These cavities have been reported in many genera. However, there are few studies on secretory cavity ontogeny in the genus Myrcia (Myrtaceae) as well as the effects of luminosity and seasonality on such secretory cavities. Therefore, the objective of this study was to provide new information regarding the ontogenesis, structure, histochemistry, and effects of seasonality in Myrcia splendens (Sw.) DC. We collected and analyzed leaves from 10 specimens of M. splendens exposed to sun and shade during both the wet and dry seasons. The samples were subjected to standard anatomical techniques for light microscopy. Myrcia splendens has schizo-lysigenous ontogenesis with exudates composed of lipids, essential oils, oil-resins, and alkaloids. The largest secretory cavities were found in leaves exposed to sunlight during the dry season. The presence of lipophilic compounds may be an important strategy for protecting the plant from herbivores. The seasonal variations observed in the leaf’s secretory cavities demonstrate the anatomical plasticity of such species to the availability of light and water. As the total area of the leaf cavities in M. splendens reflects the seasonal variation, this should be taken into account when aiming to grow crops for producing essential oils or for alkaloid extractions.