Carotenoids are the precursors of important fragrance compounds in several flowers. For example, a 2010 study of ionones in
Osmanthus fragrans Lour. var.
aurantiacus determined its essential oil contained the highest diversity of carotenoid-derived volatiles among the flowering plants investigated. A
cDNA encoding a carotenoid cleavage enzyme, OfCCD1, was identified from
transcripts isolated from flowers of
O. fragrans Lour. The recombinant enzymes cleaved carotenes to produce α-ionone and β-ionone in
in vitro assays. The same study also discovered that carotenoid content, volatile emissions, and OfCCD1 transcript levels are subject to
photorhythmic changes, and principally increased during daylight hours. At the times when OfCCD1 transcript levels reached their maxima, the carotenoid content remained low or slightly decreased. The emission of ionones was also higher during the day; however, emissions decreased at a lower rate than the transcript levels. Moreover, carotenoid content increased from the first to the second day, whereas the volatile release decreased, and the OfCCD1 transcript levels displayed steady-state oscillations, suggesting that the
substrate availability in the cellular compartments is changing or other regulatory factors are involved in volatile
norisoprenoid formation. The formation of ionones proceeds by a process mediated by the
carotenoid dioxygenases. ==Organic synthesis==