Lilium brownii (F. E. Brown) Miellez var. colchesteri E. H. Wilson has a unique characteristic in its flower color, which changes from yellowish-cream to white one day after anthesis. To elucidate the mechanism of flower color change in this species, the content and composition of carotenoids were analyzed during two days of anthesis. The major carotenoids that contributed to the yellowish-cream color of the tepals were lutein, zeaxanthin, and β-carotene. Analysis showed an obvious decrease in total carotenoid content of the tepal, indicating that the flower color change is caused by the reduction of the total carotenoid content after anthesis. To reveal the factor that controls carotenoid content in the tepals, we isolated carotenoid cleavage dioxygenase 4 (LbCCD4) gene and analyzed the number of LbCCD4 messages by quantitative real-time PCR. The transcription level of LbCCD4 gene increased and reached the maximum level 12 hours after anthesis. The results suggest that the carotenoids in yellow tepals of L. brownii var. colchesteri degraded into colorless compounds by carotenoid cleavage dioxygenase and subsequently resulted in white flowers.
Lilium brownii var. colchesteri has unique and ornamental floral characteristics in graceful harmony with flower and anther colors, flower shape, elegant fragrance, and flower color change from yellowish cream to white during anthesis. There are, however, few accessions conserved in Japan up to the present, and they often show abnormally shaped flowers and mosaic leaves seemingly due to virus infection. Virus-free bulblets were established by combining meristematic tip culture and chemotherapy. At initial diagnosis with RT-PCR, Cucumber mosaic virus (CMV), Lily mottle virus (LMoV) and Lily symptomless virus (LSV) were detected from leaf tissues of the mother plants. All regenerated bulblets obtained by meristematic tip culture of the mother plants were still infected by at least one of the viruses. The meristematic tip of the bulblets infected with either LSV or LMoV was selected for subsequent culture with 2,4-dioxohexahydro-1,3,5-triazine (DHT), an antiviral chemical. LSV was eliminated successfully in mericlones from bulblets with LSV, whereas LMoV was not from those with LMoV. The virusfree bulblets were transferred to new medium without DHT, and multiplied by in vitro scaling. They were then acclimated in a phytotron glass room at 20°C. The plants were confirmed to be virus-free after 18-months' acclimation. It was concluded that the combination of meristem tip culture and chemotherapy is practical for producing virus-free plants of L. brownii var. colchesteri.
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