Ionone

Abstract: Saffron, the processed stigma of Crocus sativus, is characterized by the presence of several apocarotenoids that contribute to the color, flavor, and aroma of the spice. However, little is known about the synthesis of aroma compounds during the development of the C. sativus stigma. The developing stigma is nearly odorless, but before and at anthesis, the aromatic compound -ionone becomes the principal norisoprenoid volatile in the stigma. In this study, four carotenoid cleavage dioxygenase (CCD) genes, CsCCD1a, CsCCD1b, CsCCD4a, and CsCCD4b, were isolated from C. sativus. Expression analysis showed that CsCCD1a was constitutively expressed, CsCCD1b was unique to the stigma tissue, but only CsCCD4a and -b had expression patterns consistent with the highest levels of -carotene and emission of -ionone derived during the stigma development. The CsCCD4 enzymes were localized in plastids and more specifically were present in the plastoglobules. The enzymatic activities of CsCCD1a, CsCCD1b, and CsCCD4 enzymes were determined by Escherichia coli expression, and subsequent analysis of the volatile products was generated by GC/MS. The four CCDs fell in two phylogenetically divergent dioxygenase classes, but all could cleave -carotene at the 9,10(9,10) positions to yield-ionone. The data obtained suggest that all four C. sativus CCD enzymes may contribute in different ways to the production of -ionone. In addition, the location and precise timing of -ionone synthesis, together with its known activity as a fragrance and insect attractant, suggest that this volatile may have a role in Crocus pollination. Crocus sativus is a triploid sterile plant characterized by its long red stigmas. These stigmas, when desiccated, constitute the spice known as saffron. Saffron is considered a complex mixture of volatile and non-volatile compounds that contribute to its overall aroma and flavor. The main components of saffron responsible for coloring strength are the derived carotenoids cis- and trans-crocins, picrocrocin, and its degradation product, the odor-active safranal that composes up to 70% of total volatiles (1). In addition to safranal, 150 volatile compounds are estimated to be present in the spice, and60 constituents have been identified (2). The structures of several of these reveal an isoprenoid-based origin like safranal, and are assumed to be the

Abstract: The Arabidopsis carotenoid cleavage dioxygenase 4 (AtCCD4) is a negative regulator of the carotenoid content of seeds and has recently been suggested as a candidate for the generation of retrograde signals that are thought to derive from the cleavage of poly-cis-configured carotene desaturation intermediates. In this work, we investigated the activity of AtCCD4 in vitro and used dynamic modeling to determine its substrate preference. Our results document strict regional specificity for cleavage at the C9-C10 double bond in carotenoids and apocarotenoids, with preference for carotenoid substrates and an obstructing effect on hydroxyl functions, and demonstrate the specificity for all-trans-configured carotenes and xanthophylls. AtCCD4 cleaved substrates with at least one ionone ring and did not convert acyclic carotene desaturation intermediates, independent of their isomeric states. These results do not support a direct involvement of AtCCD4 in generating the supposed regulatory metabolites. In contrast, the strigolactone biosynthetic enzyme AtCCD7 converted 9-cis-configured acyclic carotenes, such as 9-cis-ζ-carotene, 9'-cis-neurosporene, and 9-cis-lycopene, yielding 9-cis-configured products and indicating that AtCCD7, rather than AtCCD4, is the candidate for forming acyclic retrograde signals.

Abstract: The effects of chemical modifications, esterification or reductive alkylation, on binding properties of several terpenes by beta-lactoglobulin were examined. As shown by fluorescence quenching, beta-lactoglobulin and its derivatives bind beta-ionone, but it does not bind alpha-ionone, neither geraniol nor R(+)- and S(-)-limonene. It is suggested that its binding site, presumably situated within the calyx-shaped protein fold (North, A. C. T. Int. J. Biol. Macromol. 1989, 11, 56-58), has a narrow specificity to the structure formed by the conjugated double bonds of the beta-ionone ring and isoprenoid chain, present in both terpenes--beta-ionone and retinol. The complexes of beta-ionone with the derivatives of beta-lactoglobulin (except N-ethyllysyl-BLG) exhibit lower Kd' values than that of the complex of beta-ionone with unmodified beta-lactoglobulin. N-Methyllysyl-BLG and EtBLG are binding beta-ionone stronger than the other even more extensively modified derivatives as, for example, N-ethyllysyl-BLG and MetBLG. The partial loss of BLG beta-barrel structure achieved during extensive esterification producing MetBLG, deduced from the analysis of circular dichroism spectra, could explain its less effective binding to beta-ionone.