Abstract
Crocus sativus is the source of saffron spice, the processed stigma which accumulates glucosylated apocarotenoids known as crocins. Crocins are found in the stigmas of other Crocuses, determining the colourations observed from pale yellow to dark red. By contrast, tepals in Crocus species display a wider diversity of colours which range from purple, blue, yellow to white. In this study, we investigated whether the contribution of crocins to colour extends from stigmas to the tepals of yellow Crocus species. Tepals from seven species were analysed by UPLC-PDA and ESI-Q-TOF-MS/MS revealing for the first time the presence of highly glucosylated crocins in this tissue. β-carotene was found to be the precursor of these crocins and some of them were found to contain rhamnose, never before reported. When crocin profiles from tepals were compared with those from stigmas, clear differences were found, including the presence of new apocarotenoids in stigmas. Furthermore, each species showed a characteristic profile which was not correlated with the phylogenetic relationship among species. While gene expression analysis in tepals of genes involved in carotenoid metabolism showed that phytoene synthase was a key enzyme in apocarotenoid biosynthesis in tepals. Expression of a crocetin glucosyltransferase, previously identified in saffron, was detected in all the samples. The presence of crocins in tepals is compatible with the role of chromophores to attract pollinators. The identification of tepals as new sources of crocins is of special interest given their wide range of applications in medicine, cosmetics and colouring industries.
Highlights
Carotenoids are a subgroup of isoprenoid compounds currently comprising over 700 structures
Probably involved in seed dispersal and pollinators attraction with high economic value are bixin in Bixa orellana [7] and crocetin in Crocus sativus (Fig. S1) [8,9]
Tepals and stigmas at preanthesis and anthesis from C. sativus (Series Crocus), C. chrysanthus (Series Biflori), C. ancyrensis, C. angustifolius and C. sieberi (Series Reticulati), C. olivieri and C. vitellinus (Series Flavi) and C. korolkowii (Series Orientales) were collected from plants growing in the Botanical Garden of CLM (Albacete, Spain), immediately frozen in liquid nitrogen and stored at 280uC until required
Summary
Carotenoids are a subgroup of isoprenoid compounds currently comprising over 700 structures. The total content in crocins, the glucosylated crocetin derivatives, follows the same pattern as the levels of crocetin, but remains high in the mature stages up to anthesis [17] These compounds have been detected in the style and ovaries of senescent flowers and in the developing corm, where they are transported from the senescent stigma using the vascular system [18]. The flowers of Crocus (Iridaceae) show variability in tepal colour ranging from white, yellow, pale-brown, purple to lilac, mauve and blue. As crocins have been mainly studied in the stigmas of most Crocus species [16], we wished to determine whether a crocin biosynthesis pathway was actively contributing to the yellow colour of spring Crocus tepals and how this pathway was regulated in this tissue
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
