Flavonol 3-O-glucosides esterified with ferulic or p-coumaric acid at posi-tions 3¢¢ and 6¢¢ are the major UV-B screening pigments of the epidermal layer of Scots pine (Pinus sylvestris) needles. The last steps in the biosyn-thesis of these compounds are catalyzed by enzymes that transfer the acyl part of hydroxycinnamic acid CoA esters to flavonol 3-O-glucosides. A newly developed enzyme assay revealed three flavonol 3-O-glucoside hydroxycinnamoyltransferases (HCTs) in Scots pine needles with specifici-ties for positions 3¢¢,4¢¢ or 6¢¢. .
