Unveiling the osmophores of Philodendron (Araceae)

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Philodendron, a species-rich genus of the arum family (Araceae), is thermogenic and produces strong inflorescence scents for pollinator attraction. However, the precise location of the scent-emitting tissue and its ultrastructure were hitherto unknown.

Fertile stamens of Philodendron adamantinum.
Fertile stamens of Philodendron adamantinum. (A) Diagram showing the distribution of flower types on the spadix; in the apical region are fertile staminate flowers, in the middle region are staminodes, and in the basal region pistillate flowers. (B) Longitudinal section of a staminate flower highlighting the sterile apical portion where phenolic substances accumulate in some of the parenchyma cells and the microsporangia; the arrow indicates the single central vascular bundle. Letters d and e indicate the position of the transverse sections shown in (D) and (E), respectively. (C) Apical surface of the stamens showing the homogeneously papillose epidermis. The inset shows a stoma located on this surface; note a residue in a stomata pore. (D) Transverse section of the sterile, apical portion; note the papillose epidermis and the absence of vascular tissues; here cells with dense cytoplasm occur among phenolic-accumulating cells. (E) Transverse section of the anther region showing the microsporangia and the vascular bundle; note the absence of papillae on the epidermal cells. (F and G) Detail of secretory cells of the apical portion of a fertile stamen. (F) At 8 h prior to release of odour; note the cells with dense protoplast. (G) At 24 h after the release of odour; note the intense vacuolization of the cells and phenolic epidermis. (ep, epidermis; st, secretory tissue; vb, vascular bundle).

Gonçalves-Souza et al. show that the distal portion of both fertile and sterile staminate flowers function as osmophores in Philodendron adamantinum. The papillose epidermal cells of the distal portion of fertile stamens and staminodes are characterised by dense cytoplasm and large nuclei; the composition of organelles here is compatible with secretory activity, as indicated by the great number of mitochondria and plastids. In this portion, lipid droplets were observed, that were consumed concomitantly with the release of odour. These results indicate a functional link between thermogenesis and volatilisation of osmophore secretions to produce olfactory signals for attracting specialised beetle pollinators.

Reference

Gonçalves-Souza, P., Schlindwein, C., Dötterl, S., & Paiva, E. A. S. (2017). Unveiling the osmophores of Philodendron adamantinum (Araceae) as a means to understanding interactions with pollinators. Annals of Botany, mcw236. https://doi.org/10.1093/aob/mcw236


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