Kinetin-Mediated Stimulation of Accumulation of Buckwheat Flavonoids in the Dark

Abstract

A short treatment of excised buckwheat cotyledons with a solution of kinetin lead to an up to 9-fold stimulation of anthocyanin biosynthesis, to an about 50 percent increase in the accumula­tion of rutin, and to an about 30 percent increase, on the average, in the accumulation of C-glycosylflavones in the treated material during its posttreatment incubation in the dark. When the treated cotyledons were incubated in a solution of ʟ--phenylalanine anthocyanin accumulation in the dark practically attained the same high level as it was observed in the illuminated cotyledons fed with exogenous ʟ--phenylalanine. In experiments with l4C-labelled L-phenylalanine kinetin induced a sharp rise in the labelling (resp. in the utilization of exogenous substrate for biosynthesis) of anthocyanins and rutin in the dark and a slight increase in the radioactivity of C-glycosylflavones. Similar labelling changes occurred in the illuminated cotyledons. However, both kinetin and light still more effectively promoted biosynthetic use of the endogenous sub­strate. As a result the relative portion of flavonoids formed from exogenous L-phenylalanine under these conditions showed a decrease as compared with the ratio of precursor use in the un­treated cotyledons. The results show that low accumulation rates of anthocyanins and other flavo­noids in the dark are conditioned by the limited access of substrate (ʟ--phenylalanine) molecules to the flavonoid enzymes lending further support to the idea that flavonoid biosynthesis is normally controlled at the substrate rather than at the enzymic level.

Managing Phenol Contents in Crop Plants by Phytochemical Farming and Breeding—Visions and Constraints

“…Cytokinin : Several studies revealed promotion of phenylpropanoid bisoynthesis and accumulation in plant tissues by the action of cytokinins with an enhancement of PAL activity [ 197 , 198 ], an accumulation of total phenolics [ 199 , 200 ] and anthocyanins [ 201 – 204 ]. Cytokinin induced the accumulation of flavanones in Prunus callus cultures and phloem tissues of cherry shoots and alters the flavonoid profile of these tissues [ 166 , 206 ] ( Table 8 ).…”

ʟ-Tyrosine as a Precursor of Flavonoids in Buckwheat Cotyledons

“…Kinetin has been shown to increase the avail ability of endogenous L-phenylalanine for flavonoid biosynthesis in buckwheat cotyledons and to reduce the relative incorporation of exogenous phenylala nine [17]. Likewise, kinetin reduced the incorpora tion of exogenous tyrosine into flavonoids, especially the C-glycosylflavones (Fig.).…”

“…F la vo n o id a ssa y a n d ra d io a c tiv ity m e a s u re m e n ts Anthocyanins were determined photometrically, rutin and individual C-glycosylflavones likewise after their separation by two-dimensional paper chromatography as described elsewhere [17]. R adio activity of separate flavonoids was assayed in the ethanolic eluates with the use of a Beckman LS-100C liquid-scintillation counter [17].…”

“…R adio activity of separate flavonoids was assayed in the ethanolic eluates with the use of a Beckman LS-100C liquid-scintillation counter [17]. P A L a n d T A L a ssa y Activities of the two am monia lyases were d eter mined by the amounts of cinnamic acid or pcoumaric acid, respectively, formed during incuba tion for 4 h at 35 °C [18].…”

“…P A L a n d T A L a ssa y Activities of the two am monia lyases were d eter mined by the amounts of cinnamic acid or pcoumaric acid, respectively, formed during incuba tion for 4 h at 35 °C [18]. different from the ratio of their accum ulation, with the relative labelling always being highest in anthocyanins and, within the C-glycosylflavones, being higher in the luteolinic C-glycosylflavones orientin and isoorientin than in their apigeninic analogues vitexin and isovitexin, respectively [17,19,20]. In the present study, label from exogenous L-tyrosine, at a background of much lower general labelling, showed essentially the same pattern of distribution between individual flavonoids (Table IV), even though the relative incorporation rates of tyrosine and phenylalanine into separate flavonoids did not fully coincide.…”