Mandevilla venulosa is an endemic species of rocky outcrops in high-altitude fields of the Serra da Pedra Branca, located in Caldas, Minas Gerais, Brazil, within the Atlantic Forest phytogeographic domain. Secretory structures are common in Apocynaceae and may provide useful anatomical and taxonomic information. This study aimed to describe the anatomy and histochemistry of colleters and laticifers in M. venulosa. Fresh vegetative samples were collected and processed using standard microscopy techniques and subjected to histochemical tests. The colleters observed correspond to the standard type, composed of a central parenchymatic region surrounded by a uniseriate palisade secretory epidermis, with dense cytoplasm and a thin cuticle. During the secretory phase, they release a viscous and translucent fluid. The secretion contains polysaccharides, mucilage, pectins, and proteins, compounds associated with protection against desiccation and microbial activity. Articulated and anastomosing laticifers occur in all vegetative organs, forming early in development and producing latexes with organ-specific chemical compositions: a milky, hydrophobic latex in aerial parts (rich in lipids, terpenoids, alkaloids, and phenolics) and a yellow, hydrophilic latex in the tuberous root (containing polysaccharides, mucilage, proteins, and phenolics). Colleters are involved in protecting developing regions and preventing the desiccation of young organs. On the other hand, laticifers contribute to herbivory control due to their phenolic composition. This study contributes to the anatomical knowledge of secretory structures in Mandevilla. Notably, it provides the first evidence that latex composition may vary among different organs within the same species, highlighting the relevance of including subterranean structures in future studies to better understand latex diversity in the genus.
Bueno et al. (Mon,) studied this question.