Color and chirality: carotenoid self-assemblies in flower petals

As a novel phenomenon, optical activity often very strong - has been detect ed by circular dichroism (CD) spectroscopy in carotenoid-containing living flowers of several species belonging to different families. Using natural p ure xanthophyll. esters, very similar CD spectra were obtained in vitro, pr oving the ability of these molecules to form chiral self-assemblies. The re lationship between the ultrastructure of the chromoplast, its chemical comp osition and the optical activity is discussed. The applicability of CD spec troscopy for studying intact plant tissue is emphasized.