Abstract
The patterns of flavonoids accumulating in epidermal and mesophyll cells of barley primary leaves exhibited quantitative and qualitative differences. The main flavonoid saponarin could be detected at an about 10-times higher concentration in the epidermis as compared to the mesophyll. Flavonoids were predominantly localised in the vacuolar fraction. In order to analyze the flavonoid-uptake mechanism at the tonoplast, vitexin was chosen as a flavone glycoside structurally related to the endogenously occuring glycosides. In the presence of MgCl2 or sodium ATP, vitexin was not, or only at slow rate, taken up by isolated mesophyll vacuoles. The uptake rate was stimulated severalfold after addition of MgATP. Uptake was roughly linear with time. Between 2.5 and 40 μM, saturation was not observed. The data suggest the existance of a H+-antiporter which catalyzes the transfer of flavonoid glycosides across the tonoplast and allows for their accumulation in the vacuole.
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