UV-B induction of flavonoid biosynthesis in Scots pine (Pinus sylvestris L.) seedlings

Cultivation of Scots pine (Pinus sylvestris L.) seedlings under simulated global radiation including the UV-B band (280-320 nm; 220 mW m(-2) UV-B(BE)) led to increased formation of the diacylated flavonol glucosides 3",6"-di-p-coumaroyl-astragalin and 3",6"-di-p-coumaroylisoquercitrin in primary and cotyledonary needles, respectively. 3",6"-Di-p-coumaroyl-astragalin was also the main constitutive diacylated flavonol glucoside in both needle types. This compound predominantly accumulated in primary needles upon UV-B irradiation, and reached concentrations of 2.4 my mol g(-1) fresh weight (fw). Its concentration was only weakly affected in cotyledonary needles. 3", 6"Di-p-coumaroyl-isoquercitrin was mainly induced in cotyledonary needles with maximum concentrations of 0.8 to 0.9 my mol g(-1) fw, but was virtually unaffected in primary needles under the same irradiation conditions. Pulse labelling with L-(U(- 14)C phenylalanine revealed that these metabolites were formed de novo. Phenylal anine ammonialyase (EC 4.3.1.5) and chalcone synthase (EC 2.3.1.74) were only slightly induced by the UV-B treatment. The results described here represent the first report on UV-B-induced flavonoid biosynthesis in a conifer species.