Floral attractants in the black orchid Brasiliorchis schunkeana (Orchidaceae, Maxillariinae): clues for presumed sapromyophily and potential antimicrobial activity

Abstract

Background Orchids have evolved various strategies that aim to ensure their reproduction success. These may include the production of rewards for pollinators, or on the contrary, deception. Specific sets of features such as flower morphology, color, nectar, and odor presence (or lack thereof) are considered to determine suitability for pollination by different groups of animals. Stingless bees are thought to be the primary pollinators of the orchids of the Neotropical subtribe Maxillariinae. However, almost black flowered Brasiliorchis schunkeana at first glance presents floral adaptations that may suggest another pollination syndrome—sapromyophily. Results A few traces of secretion were noticed on the glabrous lip callus and lip apex built by conical to villiform papillae (SEM analysis). Histochemical studies revealed huge amounts of lipids in the epidermis, subepidermis, and some parenchyma cells (SBB test) with various stages of lipids accumulation between cells. Further TEM analysis showed a heterogeneous (lipoid and phenolic) nature of secretion. The dense osmiophilic cytoplasm contained organelles (RER, free ribosomes, dictyosomes, plastids with plastoglobuli, nucleus) and vesicles migrating to plasmalemma. The vesicles, osmiophilic globules, and flocculent material were visible in periplasmic space. The central vacuole possessed osmiophilic phenolic content and flocculent material. GC–MS analysis revealed in floral extract the presence of 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione (77.06%) and 2,5-di-tert-butyl-1,4-benzoquinone (16.65%). Both compounds are known for their biological activity. Conclusions The juxtaposition of results led us to the conclusion that the labellar tissue produces lipoid and phenolic material, which is responsible for the glossiness and rotten herring scent. This type of secretion could be classified as a phenolic resin. The chemical analysis revealed the presence of five semiochemicals that are known to be attractants for some Diptera, which together with the rest of the results constitutes a strong premise that representatives of this order could be potential pollinators of B. schunkeana. Field observations however are still needed to confirm this pollination syndrome.

Toxicological and Sedative Effects of Chipilin (Crotalaria longirostrata) Leaf Extracts Obtained by Maceration and Supercritical Fluid Extraction

“… 7 The oxaspiro compound, reported as a diketone or akyl-ketone, has been detected by GC-MS in Brasiliorchis schunkeana and Ficus religiosa seeds. 25 , 26 Several activities such as steroidal antimineralocorticoid, antiandrogen, and glucocorticoid have been reported for this compound. 27 Oleoresin obtained by SFE was characterized by the presence of 6-hydroxy-4,4,7α-trimethyl-5,6,7,7α-tetrahydrobenzofuran-2(4 H )-one (peak 4), a volatile compound isolated from Sargassum horneri with tested anti-inflammatory activity showing antitumor, antibacterial, antioxidative, and antiviral activities.…”

Phytochemical profiles and antimicrobial activity of the inflorescences of Sorbus domestica, S. aucuparia, and S. torminalis

“…It is expected that some floral metabolites can be synthesized by plants to attract pollinating insects. Among these, 7,9-di-tert-butyl-1-oxaspiro(4,5)deca-6,9-diene-2,8-dione, revealed in the inflorescences of S. domestica, was also detected by Lipińska et al (2022) in the floral extract of black orchid Brasiliorchis schunkeana as the attractant with the potential antimicrobial activity. Attractive function, possibly, may be performed by the common for the studied Sorbus inflorescences saturated hydrocarbon 2-methylhexacosane, which is an insect pheromone (Spikes et al, 2010).…”