Sweet smell of excess
Mutations occurring in vegetative tissues
and causing a visible change in the plant are known as sports; depending on the
mutation in question and on the cell lineage in which they occur, the changes
resulting from sports range from colour variation to alterations in morphology.
Moss roses, first described clearly in the early 18th century, are good
examples of this type of variation. They derive their name from a moss-like
growth on the calyx and pedicel. This mossy growth produces a sticky and odoriferous
exudate which, in Rosa × damascena,
the Damask rose, studied by Caissard et al. (Saint-Etienne and
Villeurbane, France, pp. 231–238), increases the complexity of the
fragrance produced by the flowers themselves. Of course, the growth is not a
moss at all: the mossy appearance is caused by a hugely excessive growth of
trichomes, including trichomes growing from trichomes. The authors were
interested to know what contribution is made to the scent of the rose by the
petals and by the ‘moss’ on the calyx and pedicel.
They stained the exudate from the trichomes in order to detect lipids and
terpenes, and also collected volatile organic compounds (VOCs) from petals and
from mossy sepals. The VOCs were analysed by gas chromatography and by gas
chromatography/mass spectrometry (GC–MS). The results are very clear: mossy
sepals and petals differ markedly in respect of the VOCs that they release. The
volatiles from the petals contain large amounts of benzenoids, particularly
phenylethanol, together with substantial quantities of monoterpenes, geraniol,
nerol and citronellol. In the mossy sepals, the majority of the VOCs are
monoterpenes, especially pinene and myrcene, while sesquiterpenes are also well
represented. This composition is similar to the composition of exudate from
non-mossy (wild-type) sepals but, of course, in the mossy sport these compounds
are exuded in much larger amounts and have a major effect on the odour of the
rose.
Professor J. A. Bryant
University of Exeter, UK
j.a.bryant{at}exeter.ac.uk
