Floral resins of Philodendron adamantinum (Araceae): secretion, release and synchrony with pollinators

Abstract

Philodendron is the only genus of Araceae in which resin release occurs in the inflorescence. The resinous secretion adheres to the smooth body surface of the pollinating scarab beetles and allows attachment of pollen grains, making its transport possible. In order to understand the process of resin synthesis and release to the external environment, we used structural, ultrastructural and histochemical analyses at different stages of development of the inflorescences of Philodendron adamantinum. Two types of secretory canals were observed in the spathe: small caliber canals near the abaxial face, and larger caliber canals in the adaxial region. Only the latter canals release secretion into the external environment. The secretory epithelium in these canals is formed by a layer of cuneiform cells, and exhibits secretory activity throughout the development of the spathe. Resin exudation is a peculiar characteristic of these canals and appears to result from pressure exerted by the secretory epithelium and by structural modifications in the wall of cells adjacent to the epidermis, which allow the formation of a separation zone whereby the resin is released. The observed synchrony between anther dehiscence and resin exudation of P. adamantinum enhances the role of this secretion in the pollination process.

New Aspects of Secretory Structures in Five Alismataceae Species: Laticifers or Ducts?

“…Notably, the resin ducts of Alismataceae are narrow and lack a sheath (this study), as observed in the ducts of Clusiaceae [29,44]. Sheaths formed by two cell layers surrounding the duct occur in Anacardiaceae [45], Hypericaceae [46], and Araceae [47]. Narrow secretory ducts are not common in angiosperms, but they have also been reported in Philodendron adamantinum Mart.…”

“…Narrow secretory ducts are not common in angiosperms, but they have also been reported in Philodendron adamantinum Mart. ex Schott (Araceae) [47] and Hypericum perforatum L. (Hypericaceae) [46].…”

“…In the present study, epithelial cells have thin walls [44,48], dense cytoplasm mainly during the secretory phase, a fact also observed in Garcinia mangostana L. (Clusiaceae) [49] and Clusia species [29,44], in addition to large vacuoles and many mitochondria, plastids and Golgi apparatus. For Araceae, two types of secretory ducts have been described: one of small diameter in which the secretion accumulates in its lumen and is related to plant defense, with release of the secretion occurring only in the case of injury, and the other of large diameter that releases resin into the external environment and is directly related to the pollination mechanism, having the function to guarantee pollen adherence, specifically present in the adaxial part of the spathe of the inflorescence [47]. The first one is the most common in species of the family and is distributed in roots, stem, leaves and floral organs [47,50].…”

True nectar or stigmatic secretion? Structural evidence elucidates an old controversy regarding nectaries in Anthurium

“…This lack of structural studies of secretory activity has resulted in considerable controversy about the presence of floral nectaries or even true nectar secretion in this genus (see Hartley et al, 2017). The occurrence of secretory activity in Araceae inflorescences has been documented for some species, but only in rare studies has a structural analysis identified the origin of the secretory product (Skubatz and Kunkel, 1999; Hadacek and Weber, 2002; Gonçalves‐Souza et al, 2017, 2018). Our study demonstrated the existence of active tepalar nectaries in Anthurium andraeanum .…”

Pollination ecology and floral scent chemistry of Philodendron fragrantissimum (Araceae)

“…In some Philodendron, the cyclocephaline scarabs were also observed to lick the abundant exudates from receptive stigmas (Gottsberger et al 2013). In general, fertile staminate and pistillate flowers are not heavily damaged by the feeding activity, even during the male phase when temporarily resident cyclocephaline scarabs eat copious amounts of pollen (Gibernau et al 1999;Gottsberger et al 2013;Pereira et al 2014;Maldonado et al 2015; but see Gonçalves-Souza et al 2018 for an exception). This feeding preference is explained by lower quantities of calcium oxalate crystals (e.g.…”