Patterns and roles of lignan and terpenoid accumulation in the reaction zone compartmentalizing pathogen-infected heartwood of Norway spruce

Abstract

Main conclusion Lignan impregnation of the reaction zone wood protects against oxidative degradation by fungi. Traumatic resin canals may play roles in the underlying signal transduction, synthesis, and translocation of defense compounds. Abstract Tree defense against xylem pathogens involves both constitutive and induced phenylpropanoids and terpenoids. The induced defenses include compartmentalization of compromised wood with a reaction zone (RZ) characterized by polyphenol deposition, whereas the role of terpenoids has remained poorly understood. To further elucidate the tree–pathogen interaction, we profiled spatial patterns in lignan (low-molecular-weight polyphenols) and terpenoid content in Norway spruce (Picea abies) trees showing heartwood colonization by the pathogenic white-rot fungus Heterobasidion parviporum. There was pronounced variation in the amount and composition of lignans between different xylem tissue zones of diseased and healthy trees. Intact RZ at basal stem regions, where colonization is the oldest, showed the highest level and diversity of these compounds. The antioxidant properties of lignans obviously hinder oxidative degradation of wood: RZ with lignans removed by extraction showed significantly higher mass loss than unextracted RZ when subjected to Fenton degradation. The reduced diversity and amount of lignans in pathogen-compromised RZ and decaying heartwood in comparison to intact RZ and healthy heartwood suggest that α-conindendrin isomer is an intermediate metabolite in lignan decomposition by H. parviporum. Diterpenes and diterpene alcohols constituted above 90% of the terpenes detected in sapwood of healthy and diseased trees. A significant finding was that traumatic resin canals, predominated by monoterpenes, were commonly associated with RZ. The findings clarify the roles and fate of lignan during wood decay and raise questions about the potential roles of terpenoids in signal transduction, synthesis, and translocation of defense compounds upon wood compartmentalization against decay fungi.

Trunk Injection as a Tool to Deliver Plant Protection Materials—An Overview of Basic Principles and Practical Considerations

“…Based on the CODIT concept, after an injury, trees respond by blocking the decaycausing organisms, mostly fungi and bacteria, from moving horizontally or vertically through the formation of four walls. Walls 1-3 comprise the reaction zone, where lignin formation protects against further oxidative degradation [56]. Wall 4 is the barrier zone.…”

An analysis of stand-level size distributions of decay-affected Norway spruce trees based on harvester data

“…Our findings indicate that trees with incipient decay are on average larger and taller compared with trees with advanced decay. This is expected, since the proportion of water-conductive stem sapwood decreases along with advancement of decay, while at the same time, the affected trees allocate more carbon to tree defense phenolics at the interface between pathogen-colonized wood and inner sapwood (Bendz-Hellgren and Stenlid 1995;Oliva et al 2012;Nagy et al 2022). Because the heights of the harvested trees were predicted using conventional taper curves, the effect of decay on the growth rates was neglected, which may result in overpredictions of heights associated with decay-affected trees.…”

Fungal succession in decomposing ash leaves colonized by the ash dieback pathogen Hymenoscyphus fraxineus or its harmless relative Hymenoscyphus albidus

“…The quality of ash leaf litter is obviously affected by H. fraxineus as the infected leaves show accumulation of host defense phenolics (Nielsen et al, 2022), which may have potential microbe toxicity or inhibitory effects on microbial enzyme activity. This may partially explain the low level of Agaricomycetes in petioles from the diseased forest as phenolic compounds can suppress oxidative radicals utilized by basidiomycetes to break down the lignocellulose matrix (e.g., Nagy et al, 2022). It is also noteworthy that the correlations between weight loss, FungiQuant Cq values, and total DNA level were low for petioles from the diseased site in comparison to the healthy site.…”