Flowers are scented because they emit volatile compounds that are perceived by humans and other organisms. Usually several compounds are emitted simultaneously (up to 40 in the case of roses). The patterns of emission are regulated by the relative maturity of the flowers as they open and also environmentally (light being the major factor). At The Department of Agricultural Sciences, Wye, England, researchers are revealing why flowers of Rosa damascena also show rhythmic cycles of emission — peaking every day in the afternoon for sevarl days even in continuous light or dark. This suggests that the whole spectrum of volatile compounds is regulated and coordinated by master genes or signals that control suites of enzymes required for each biosynthetic pathway. Some of these volatile compounds might be pre-formed in the flower to be released following an enzymic reaction or they may be the result of new biosyntheis or a combination of both. It is hoped that the research will shed light on why so many modern rose varieties are devoid of scent and provide techniques to re-introduce scent or to alter the timing of emission, for example to generate night-scented roses. www.wye.ac.uk/plant