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

WIEMER, A.P.; MORÉ, M.; BENITEZ-VIEYRA, S.; COCUCCI, A.A.; RAGUSO, R.A.; SÉRSIC, A.N.

PLANT BIOLOGY

Año: 2009 vol. 11 p. 506 - 514

1435-8603

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