Estruturas mediadoras da polinização em philodendron adamantinum mart. ex schott (ARACEAE): morfologia e aspectos funcionais

Abstract

Philodendron adamantinum is a rupiculous species of restricted distribution, pollinated by beetles Erioscelis emarginata. This Araceae species presents several traits that favour cantharophily, such as release of attractive scents; thermogenesis; nutritive tissue; protogyny and the presence of sheltering chamber for pollinators. The release of resin in the inflorescence, which occurs exclusively in Philodendron, also assists in the pollination process. Searching for better understand the complex interaction between P. adamantinum and its specific pollinator, the relationship between structure and function of osmophores, nutritive tissue and resin secretory ducts were evaluated in this work. The osmophores are composed by scattered secretory cells in infertile apical region of the stamens and in the apex of staminodes. The staminodes present lipid reserves that are, in the most part, used in the thermogenesis and scent release. The beetles use the remaining reserves as well as cells with dense cytoplasm rich in structural compounds as food source. Added to the nutrient supply, the position of staminodes into a chamber favors protection the fertile structures against pollinators damages and keeps the beetles in the inflorescence until the pollen release. The resiniferous ducts have typical characteristics observed in other species. However, the mechanism of resin release to the external environment is first described in this work and shows strong correlation with pollinators activity. The increase in volume of the cells of duct, especially the adjacent secretory epithelium layer, results in increased pressure on the resin in the lumen. The very high pectic nature of the wall of parenchyma cells near the apex of the duct suggests a route for duct opening. Thus, combining increased pressure to a weakness point, the epidermis is ruptured and the resin overflows. The structures studied in this work mediate the interaction between P. adamantinum and its exclusive pollinator, participating in a synchronized sequence of events controlled by precise mechanisms, culminating in the pollination of this species.