CPTA modulates levels of carotenogenic proteins and their mRNAs and affects carotenoid and ABA content as well as chromoplast structure in Narcissus pseudonarcissus flowers

To investigate mechanisms leading to enhanced carotenoid formation, daffodil (Narcissus pseudonarcissus) flowers were treated with the lycopene cyclase (LYC) inhibitor CPTA. Under these conditions, chromoplasts underwent strong morphological changes and the lycopene accumulated was found sequestered in crystals. During this process the total carotenoid content increased about 2-fold. This increase was accompanied by an upregulation of the transcript levels of phytoene synthase (PSY), phytoene desaturase (PDS) and lycopene cyclase (LYC). In contrast, ζ-carotene desaturase (ZDS) was not a target for CPTA-induced upregulation, although its product lycopene was accumulated. At the protein level, CPTA induction of carotenogenic enzymes was also observed, again with the exception of ZDS. Lycopene accumulation, caused by CPTA treatment, was also accompanied by a decrease of β-carotene derivatives, especially zeaxanthin. Our data suggest that carotenoid biosynthesis may undergo an end-product regulation via an effector probably originating from a β-carotene derivative. Increased concentrations of abscisic acid (ABA) measured after CPTA treatment may be involved in this regulatory phenomenon, pointing to the presence of an additional xanthophyll-independent source of this phytohormone.