Metabolite and target transcript analyses during Crocus sativus stigma development

Saffron, the desiccated stigmas of Crocus sativus, is highly appreciated for its peculiar colour, flavour and aroma. Several studies have been conducted with the spice, but little is known about the evolution of volatile and non-volatile compounds generated during the development of the stigma. In this study, we have followed these compounds, with special attention to those of isoprenoid origin (carotenoids and monoterpenes), which are responsible for the organoleptic properties of saffron. The main compounds that accumulated throughout stigma development in C. sativus were crocetin, its glucoside derivatives and picrocrocin, all of which increased as stigmas reached a fully developed stage. The volatile composition of C. sativus stigmas changed notably as stigmas developed with each developmental stage being characterized by a different volatile combination. In red stigmas, beta-cyclocitral, the 7,8 cleavage product of beta-carotene, was highly produced, suggesting the implication of both beta-carotene and zeaxanthin in crocetin formation. As stigmas matured, hydroxy-beta-ionone and beta-ionone were produced while safranal, the most typical aroma compound of the processed spice, was only detected at low levels. However, a safranal-related compound 2,2,2-trimethyl-2-cyclohexene-1,4-dione (4-oxoisophorone) increased rapidly at the anthesis stage and also in senescent stigmas. Monoterpenes were mainly emitted at the time of anthesis and the emission patterns followed the expression patterns of two putative terpene synthases CsTS1 and CsTS2. Fatty acid derivates, which predominated at the earlier developmental stages, were observed at low levels in later stages.