FLAVONOID BIOSYNTHESIS IN FLOWER PETALS OF 5 LINES OF LISIANTHUS (EUSTOMA-GRANDIFLORUM GRISE)

The biosynthesis of flavonoid pigments during petal development was investigated in five lines of lisianthus (Eustoma grandiflorum Grise.), with purple, pink, mauve or white flowers (W42 and W84). Flavonols were found at high levels at all stages of petal development, but peaked just prior to flower opening. In the cyanic lines, anthocyanins were first detected in opening flowers, increasing in amounts thereafter. The polymerase chain reaction was used to generate cDNAs from lisianthus petal RNA for phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI) and dihydroflavonol 4-reductase (DFR), and expression of their corresponding mRNAs during petal development investigated. In the cyanic lines, PAL, CHS and CHI transcripts were present throughout petal development, with peak expression in young, acyanic buds. DFR expression was low in young buds and peaked immediately preceding anthocyanin synthesis. Thus, the activity of the biosynthetic genes correlated closely with the flavonoid content of the petals, with the synthesis of flavonols being temporally separated from that of anthocyanins. Transcripts for all four genes examined were detected in both white-flowered lines, although line W42 had only low levels for DFR. Neither white-flowered line could synthesize anthocyanins when petal tissue was fed with leucopelargonidin and leucocyanidin (fed to W42 only), products of the DFR enzyme. Thus, line W42 may lack activity for a regulatory factor that controls the expression of the genes of the later part of the flavonoid biosynthetic pathway, while W84 may contain a block in the conversion of leucoanthocyanidin to anthocyanin.