Induced Responses in Phenolic Metabolism in Two Norway Spruce Clones after Wounding and Inoculations with Ophiostoma polonicum, a Bark Beetle-Associated Fungus

Abstract

Two Norway spruce (Picea abies Karst.) clones, one resistant and the other susceptible to m a s inoculation with Ophiostoma polonicum Siem., were compared with regard to their phenolic compositions and chalcone synthase (CHS) and stilbene synthase activities of their phloem before and at 6 and 1 2 d after artificial inoculation with sterile malt agar or O. polonicum. In unwounded phloem, the resistant clone differed from the susceptible clone by the presence of taxifolin glycoside, lower concentrations of stilbene glycosides, and higher CHS activity. After inoculation, (+)-catechin concentration and CHS activity dramatically increased around the wound, particularly in the resistant clone. Stilbene synthase activity also increased, but more slowly and to a lower level, whereas the concentrations of stilbenes remained stable. Tanning ability decreased in the susceptible clone, whereas it remained stable in the resistant one. It is proposed that the induced phenolic response of Norway spruce phloem consists of an activation of the phenolic pathway, finally leading to tannins and insoluble polymers. It is suggested that resistance to O. polonicum depends on the ability of the tree to easily activate the flavonoid pathway.

A Common Fungal Associate of the Spruce Bark Beetle Metabolizes the Stilbene Defenses of Norway Spruce

“…A number of previous studies had reported that the stilbene content of spruce bark declined during fungal attack (Brignolas et al, 1995;Viiri et al, 2001;Li et al, 2012). These declines were considered very puzzling because they occurred despite increases in the enzyme activity of STS (Brignolas et al, 1995), which catalyze the formation of the stilbene skeleton.…”

“…These declines were considered very puzzling because they occurred despite increases in the enzyme activity of STS (Brignolas et al, 1995), which catalyze the formation of the stilbene skeleton. Furthermore, increases in piceatannol concentrations (Viiri et al, 2001) and stilbene dimers (Li et al, 2012) were observed in spruce bark after C. polonica infection.…”

“…Two stilbene synthase (STS) enzymes that contribute to the biosynthesis of these compounds have been described in Norway spruce (Hammerbacher et al, 2011). These enzymes seem to play a role in tree defense, since fungal infection induced elevated amounts of STS transcript (Hammerbacher et al, 2011) and increased enzyme levels (Brignolas et al, 1995). However, there are contradictory reports on stilbene glucoside accumulation in spruce bark during fungal infection.…”

“…Significant increases in astringin were observed after inoculation of Picea glauca saplings with avirulent C. polonica (Hammerbacher et al, 2011). However, stilbene glycoside concentrations in mature Norway spruce were stable or even declined during the course of C. polonica infection (Brignolas et al, 1995;Viiri et al, 2001;Li et al, 2012).…”

Defence reactions of mature Norway spruce (Picea abies) before and after inoculation of the blue-stain fungus Endoconidiophora polonica in a drought stress experiment

“…Trees that are more resistant show significantly higher terpene levels following inoculation of E. polonica in the dark coloured zone around the entrance hole penetrated by fungal hyphae (Zhao et al 2011). Concentrations and composition of particular phenols can even predict Norway spruce resistance to inoculation of E. polonica as shown by Brignolas et al (1995Brignolas et al ( , 1998. Interestingly, pre-treatment of spruce trees with this blue-stain fungus can itself enhance defence capacities via the formation of traumatic resin ducts and activation of polyphenolic parenchyma cells (Krokene et al 2003).…”