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, daffodi l (Narcissus pseudonarcissus) flowers were treated with the lycopene cyclas e (LYC) inhibitor CPTA. Under these conditions, chromoplasts underwent stro ng morphological changes and the lycopene accumulated was found sequestered in crystals. During this process the total carotenoid content increased ab out 2-fold. This increase was accompanied by an upregulation of the transcr ipt levels of phytoene synthase (PSY), phytoene desaturase (PDS) and lycope ne cyclase (LYC). In contrast, zeta-carotene desaturase (ZDS) was not a tar get for CPTA-induced upregulation, although its product lycopene was accumu lated. At the protein level, CPTA induction of carotenogenic enzymes was al so observed, again with the exception of ZDS. Lycopene accumulation, caused by CPTA treatment, was also accompanied by a decrease of beta-carotene der ivatives, especially zeaxanthin. Our data suggest that carotenoid biosynthe sis may undergo an end-product regulation via an effector probably originat ing from a beta-carotene derivative. Increased concentrations of abscisic a cid (ABA) measured after CPTA treatment may be involved in this regulatory phenomenon, pointing to the presence of an additional xanthophyll-independe nt source of this phytohormone.