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1985 (1)
1983 (1)
1Author    U. Margna, T. VainjärvRequires cookie*
 Title    Kinetin-Mediated Stimulation of Accumulation of Buckwheat Flavonoids in the Dark  
 Abstract    A short treatment o f excised buckwheat cotyledons with a solution o f kinetin lead to an up to 9-fold stimulation o f anthocyanin biosynthesis, to an about 50 percent increase in the accum ula­ tion o f rutin, and to an about 30 percent increase, on the average, in the accum ulation o f C-glycosylflavones in the treated material during its posttreatment incubation in the dark. When the treated cotyledons were incubated in a solution o f L-phenylalanine anthocyanin accum ulation in the dark practically attained the same high level as it was observed in the illum inated cotyledons fed with exogenous L-phenylalanine. In experim ents with 14C-labelled L-phenylalanine kinetin induced a sharp rise in the labelling (resp. in the utilization o f exogenous substrate for biosynthesis) o f anthocyanins and rutin in the dark and a slight increase in the radioactivity o f C-glycosylflavones. Similar labelling changes occurred in the illum inated cotyledons. However, both kinetin and light still more effectively prom oted biosynthetic use o f the endogenous sub­ strate. As a result the relative portion o f flavonoids formed from exogenous L-phenylalanine under these conditions showed a decrease as com pared with the ratio o f precursor use in the un­ treated cotyledons. The results show that low accum ulation rates o f anthocyanins and other flavo­ noids in the dark are conditioned by the lim ited access o f substrate (L-phenylalanine) m olecules to the flavonoid enzymes lending further support to the idea that flavonoid biosynthesis is normally controlled at the substrate rather than at the enzym ic level. 
  Reference    Z. Naturforsch. 38c, 711—718 (1983); received May 2 1983 
  Published    1983 
  Keywords    Anthocyanins Flavonoids, Accum ulation Kinetin, [l4C-L]Phenylalanine, Fagopyrum esculentum 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-0711.pdf 
 Identifier    ZNC-1983-38c-0711 
 Volume    38 
2Author    U. Margna, L. Laanest, E. Margna, T. VainjärvRequires cookie*
 Title    L-Tyrosine as a Precursor of Flavonoids in Buckwheat Cotyledons  
 Abstract    Exogenous L-tyrosine was incorporated 1 3 -1 4 tim es less effectively than exogenous L-phenyl-alanine into flavonoids in excised cotyledons o f 3 days old buckw heat seedlings but proved to be an only 5 times poorer precursor when the experim ents were carried out with 5 days old material. Simultaneous administration o f L-phenylalanine m arkedly reduced incorporation o f L-tyrosine into flavonoids. A similar decrease in the utilization o f exogenous L-tyrosine for flavonoid b io­ synthesis occurred in kinetin-treated cotyledons. H owever, in cotyledons treated with high doses o f glyphosate, an inhibitor o f the shikim ic acid pathway, an increase in the formation o f flavonoids from exogenously supplied L-tyrosine was observed. Under all conditions the relative incorporation rate o f exogenous L-tyrosine was highest for anthocyanins and lowest for C-glyco-sylflavones while within the latter class o f com pounds the luteolinic derivatives orientin and iso-orientin incorporated more label than their apigeninic analogues vitexin and isovitexin. PAL and TAL activities were found to be present in the cotyledons in a ratio o f 50:1. The possible role o f L-tyrosine as an alternative natural precursor for the biosynthesis o f flavonoids and other related polyphenols is discussed. 
  Reference    Z. Naturforsch. 40c, 154 (1985); received April 24/O ctober 29 1984 
  Published    1985 
  Keywords    Anthocyanins, Flavonoids, Biosynthesis, [14C-L]Tyrosine, [14C-L]Phenylalanine, Kinetin, Glyphosate, Fagopyrum esculentum 
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 TEI-XML for    default:Reihe_C/40/ZNC-1985-40c-0154.pdf 
 Identifier    ZNC-1985-40c-0154 
 Volume    40