Abstract:Hydrolysis of bordered and pinoid pits may be a key event during colonization of wood by decay fungi. Although pits are numerous, studies of pectin-hydrolyzing enzymes in wood decay fungi are scarce, probably because of the relatively low content (less than 4 %) of pectin in wood and because of the primary focus on understanding the degradation of lignified components. Endopolygalacturonase (endo-PG) activity was estimated by cup-plate assay and viscosity reduction of pectin from liquid cultures of fifteen bro… Show more
“…In contrast, degradation of piceoid pit membranes in P. abies was more localised and was restricted to cells near the outer surfaces of the specimens. Previous studies have demonstrated that most brown-and white-rot fungi have the capacity to hydrolyse the pectin in pit membranes during incipient decay, which facilitates colonisation (Cowling 1961;Wilcox 1968;Green and Clausen 1999;Schwarze and Landmesser 2000;Schwarze et al 2004).…”
The present study shows that isolates of P. vitreus have an extraordinary capacity to induce substantial permeability changes in heartwood of P. abies without causing significant losses in impact bending strength. The degradation of pit membranes by P. vitreus is an important aspect that could also have significant benefits in wood protection processes. Further studies are currently in progress with the objective of optimising the uniformity of wood colonisation and duration of incubation, so as to improve the permeability of water-borne wood preservatives or hydrophobic substances applied by brushing, dipping and impregnation.
“…In contrast, degradation of piceoid pit membranes in P. abies was more localised and was restricted to cells near the outer surfaces of the specimens. Previous studies have demonstrated that most brown-and white-rot fungi have the capacity to hydrolyse the pectin in pit membranes during incipient decay, which facilitates colonisation (Cowling 1961;Wilcox 1968;Green and Clausen 1999;Schwarze and Landmesser 2000;Schwarze et al 2004).…”
The present study shows that isolates of P. vitreus have an extraordinary capacity to induce substantial permeability changes in heartwood of P. abies without causing significant losses in impact bending strength. The degradation of pit membranes by P. vitreus is an important aspect that could also have significant benefits in wood protection processes. Further studies are currently in progress with the objective of optimising the uniformity of wood colonisation and duration of incubation, so as to improve the permeability of water-borne wood preservatives or hydrophobic substances applied by brushing, dipping and impregnation.
“…In a more recent study, the same authors showed that, while grapevine summer pruning leads to the production of tylose, winter pruning essentially leads to the secretion of gels that have pectin as a major component (Sun et al 2008). Pectin is a perfect substrate for decomposition by fungi (Green et al 1996;Green and Clausen 1999). Several esca-associated wood-rot fungi, e.g.…”
Esca disease, which attacks the wood of grapevine, has become increasingly devastating during the past three decades and represents today a major concern in all wine-producing countries. This disease is attributed to a group of systematically diverse fungi that are considered to be latent pathogens, however, this has not been conclusively established. This study presents the first in-depth comparison between the mycota of healthy and diseased plants taken from the same vineyard to determine which fungi become invasive when foliar symptoms of esca appear. An unprecedented high fungal diversity, 158 species, is here reported exclusively from grapevine wood in a single Swiss vineyard plot. An identical mycota inhabits wood of healthy and diseased adult plants and presumed esca pathogens were widespread and occurred in similar frequencies in both plant types. Pioneer esca-associated fungi are not transmitted from adult to nursery plants through the grafting process. Consequently the presumed esca-associated fungal pathogens are most likely saprobes decaying already senescent or dead wood resulting from intensive pruning, frost or other mecanical injuries as grafting. The cause of esca disease therefore remains elusive and requires well executive scientific study. These results question the assumed pathogenicity of fungi in other diseases of plants or animals where identical mycota are retrieved from both diseased and healthy individuals.
“…Due to its unique multiple chemical natures, it has been receiving much attention for its various ecological qualities, such as: (i) bioremediation of a wide variety of organic pollutants (2) with lignin biodegradation systems (3-7); (ii) inactivation of copper-containing wood preservatives by wood-rotting fungi (8,9); (iii) detoxification of aluminum toxicity in Al-resistant buckwheat (10); (iv) crop damage caused by oxalic acid-producing phytopathogens (11,12); (v) the biofertilizer effect of ectomycorrhizal fungi (13,14); and (vi) being an electron source for nitrogen fixation in symbiotic rhizobia in a legume plant (15). In addition, oxalic acid is known as the general physiological trait that most brown-rot basidiomycetes, including Fomitopsis palustris, accumulate oxalic acid at greater concentrations in culture fluid, whereas white-rot ones do not because they metabolize and͞or decompose oxalic acid by various mechanisms (16)(17)(18)(19). Nevertheless, the whiterots were observed to accumulate Ca-oxalate during wood decay processes (20).…”
A metabolic mechanism for oxalic acid biosynthesis in the woodrotting basidiomycete Fomitopsis palustris has been proposed on the basis of biochemical analyses of glucose metabolism. There was a strong correlation between glucose consumption and oxalate production. Oxalic acid was found to accumulate in the culture fluid in about 80% of the theoretical yield or about 5-fold, on the basis of the fungal biomass harvested. The results clearly indicate that glucose was not completely oxidized to CO2 by the tricarboxylic acid (TCA) cycle but converted mainly to oxalate. The determination of the 12 enzymes concerned has revealed the occurrence of the unprecedented metabolic coupling of the TCA and glyoxylate cycles that support oxalate biosynthesis. In this metabolic system, isocitrate lyase (EC 4.1.3.1), together with oxaloacetase (EC 3.7.1.1), was found to play a pivotal role in yielding oxalate from oxaloacetate via the acetate-recycling routes. Moreover, malate dehydrogenase (EC 1.1.1.37), with an extraordinarily high activity among the enzymes tested, was shown to play an important role in generating NADH by oxidation of malate to oxaloacetate. Thus, it is proposed that the wood-rotting basidiomycete acquires biochemical energy by oxidizing glucose to oxalate.
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