A simple floral fragrance and unusual osmophore structure in Cyclopogon elatus (Orchidaceae)

Abstract

We studied gland morphology, anatomy and the chemical composition of the floral fragrance in the sweat bee‐pollinated orchid Cyclopogon elatus. This is apparently the first such analysis for any Cyclopogon species, and one of very few studies in which both odour and osmophore are characterised in a nectar‐rewarding orchid. Structures responsible for floral scent production were localised with neutral red staining and histochemical assays for lipids and starch. Their morphology and anatomy were studied with scanning electron microscopy and light microscopy thin sections, respectively. Fragrance samples were collected using SPME fibres and analysed with GC‐MS. Anatomical evidence suggests that two parallel oval‐shaped patches of unicellular trichomes on the abaxial surface of the labellum are osmophores. These are rich in stored lipids, while the parenchyma surrounding the vascular bundles contains starch. Only freshly opened flowers produced odours, while buds and withered flowers lacked scent. The chemical composition of the odour was dominated (>99.8%) by a single compound, trans‐4,8‐dimethyl‐nona‐1,3,7‐triene (DMNT). Gland anatomy and position on the outside of the perianth are unusual for scent glands in general. The presence of DMNT, a nearly ubiquitous compound in herbivore‐induced vegetative emissions and one of the major floral volatiles of Yucca, is not surprising in view of hypotheses on the evolutionary origin of flower scents, suggesting that wound volatiles are utilised as kairomonal attractants by florivores whose activities result in pollination.

Floral micromorphology of the genus Restrepia (Orchidaceae) and the potential consequences for pollination

“…Restrepia have been found on the abaxial side of the labellum in Cyclopogon elatus 131 (Orchidaceae) (Wiemer et al, 2009). In Wiemer's study, similar features to those found on the 132 cuticle layer in the current study were reported.…”

Morphological, histological and ultrastructural features of osmophores and nectary of Bulbophyllum wendlandianum (Kraenzl.) Dammer (B. section Cirrhopetalum Lindl., Bulbophyllinae Schltr., Orchidaceae)

“…The starch is exploited as a source of energy in fragrance production (Vogel 1990). Nevertheless, in some fragrant orchids as in Cypripedium (Swanson et al 1980), Gymnadenia conopsea (Stpiczyńska 2001), Cyclopogon elatus (Wiemer et al 2009) and Anacamptis pyramidalis f. fumeauxiana (Kowalkowska et al 2012), the plastids are starchless, as in the appendages of Bulbophyllum wendlandianum. The starchless plastids in Cypripedium were produced and emitted lipid soluble odours (Swanson et al 1980).…”

Phenotypic selection on floral scent: trade-off between attraction and deterrence?

“…Only as a rare exception, flowers emit single compounds Wiemer et al 2009), but usually fragrance consists of complex blends of VOCs originating from different biosynthetic pathways (Raguso 2008). Such bouquets are often taxon-or population specific, by means of different qualitative composition, or just different proportions of the same compounds (Chess et al 2008;Huber et al 2005;Mant et al 2005;Salzmann et al 2007a).…”