UV-B INDUCTION OF FLAVONOID BIOSYNTHESIS IN SCOTS PINE (PINUS-SYLVESTRIS L) SEEDLINGS

Cultivation of Scots pine (Pinus sylvestris L.) seedlings under simula ted 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 glucos ides 3'',6''-di-p-coumaroyl-astragalin and 3'',6''-di-p-coumaroyl-isoq uercitrin in primary and cotyledonary needles, respectively. 3'',6''-D i-p-coumaroyl-astragalin was also the main constitutive diacylated fla vonol glucoside in both needle types. This compound predominantly accu mulated in primary needles upon UV-B irradiation, and reached concentr ations of 2.4 mu mol g(-1) fresh weight (fw). Its concentration was on ly weakly affected in cotyledonary needles. 3'',6''-Di-p-coumaroyl-iso quercitrin was mainly induced in cotyledonary needles with maximum con centrations of 0.8 to 0.9 mu mol g(-1) fw, but was virtually unaffecte d in primary needles under the same irradiation conditions. Pulse labe lling with L-(U-C-14)phenylalanine revealed that these metabolites wer e formed de novo. Phenylalanine ammonialyase (EC 4.3.1.5) and chalcone synthase (EC 2.3.1.74) were only slightly induced by the UV-B treatme nt. The results described here represent the first report on UV-B-indu ced flavonoid biosynthesis in a conifer species.