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 L-phenylalanine anthocyanin accumulation in the dark practically attained the same high level as it was observed in the illuminated cotyledons fed with exogenous L-phenylalanine. In experiments with 14C-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 (L-phenylalanine) molecules to the flavonoid enzymes lending further support to the idea that flavonoid biosynthesis isnormally controlled at the substrate rather than at the enzymic level. © 1983, Walter de Gruyter. All rights reserved.