Jessie A. Micales

Efficacy of Pinosylvins against White-Rot and Brown-Rot Fungi

Summary Three stilbenes, pinosylvin (PS), pinosylvin monomethyl ether (PSM) and pinosylvin dimethyl ether (PSD), were extracted from white spruce (Picea glauca), jack pine (Pinus banksiana), and red pine (Pinus resinosa) pine cones, and their structures were confirmed by spectroscopic and chromatographic (HPLC, GC/MS, NMR and FTIR) analysis. PS, PSM, PSD or a 1:1:1 mixture of these stilbenes at concentrations of 0.1 % and 1.0 % were examined for their fungal inhibitory activity by two bioassay methods. Growth of white-rot fungi (Trametes versicolor and Phanerochaete chrysosporium), and brown-rot fungi (Neolentinus lepideus, Gloeophyllum trabeum and Postia placenta) on agar media in the presence of each of the stilbenes or a 1:1:1 mixture inhibited growth of white-rot fungi, but slightly stimulated growth of brown-rot fungi. Soil-block assays, conditions more representative of those found in nature, did not correlate with those from the screening on agar media. PS, PSM, PSD or a 1:1:1 mixture of the three compounds at concentrations of 0.1 % and 1.0 % did not impart any significant decay resistance to white-rot fungi inoculated on a hardwood (Red maple). However under the same conditions, decay resistance was observed against brown-rot fungi on a softwood (Southern yellow pine). It appears that stilbenes at least partially contribute to wood decay resistance against brown-rot fungi.

Localization and induction of oxalate decarboxylase in the brown-rot wood decay fungus Postia placenta☆

Oxalate decarboxylase (ODC), the enzyme that converts oxalic acid to formic acid and carbon dioxide, was recently isolated from high- and low-decay isolates of the brown-rot wood decay fungus Postia placenta. The enzyme is induced in the presence of concentrations of oxalic acid that inhibit growth and is associated with the hyphal surface and hyphal sheath. A probable role for ODC in P. placenta is to prevent the overaccumulation of oxalic acid, forming a nontoxic, buffered, low-pH environment that facilitates the decay process.

Carbohydrate-Degrading Complex of the Brown-Rot Fungus Postia placenta: Purification of β-1,4-Xylanase

An extremely stable extracellular glycoprotein, ß-l,4-xylanase, was isolated both by ethanol precipitation and by ultrafiltration from a crude, water-sotuble extract of sweetgum (Liquidambar styraciflua) decayed by the brown-rot fungus Postia placenta. The enzyme was funher purified and separated from the glycosidase enzymes on Fractogel 55. The molecular weight of the xylanase was estimated at 43,000 daltons by gel chromatography, SOS-PAGE, and HPLC. Activity of carboxymethylcellulase (ß-l,4-endoglucanase) enzyme comigrated electrophoretically with the xytanase. The apparent isoelectric focus point of the xylanase was estimated äs 3.8. The carbohydrate content of the xylanase ranged between 48% and 59% (w/w) depending upon the method of Isolation. The resistance of the xylanase fraction to denaturation or inactivation by SDS-2ME, urea, and guanidine-HCI is likely caused by the protective capacity of the high carbohydrate content of the glycoprotein.

Physiological Characteristics of a Non-Degradative Isolate of Postia (equivalent to Poria) placenta

Decay capacity of 14 strains of the brown-rot fungus Postia (≡ Poria) placenta was determined using soil-wood block tests. One monokaryotic isolate, ME20, was identified as being unable to degrade wood. It retained the ability to produce extracellular carbohydrate-degrading enzymes. although levels of glycosidases and carboxymethylcellulase were atypical under certain cultural conditions. The electrophoretic protein profile of this isolate varied from degradative strains. It produced H 2O 2 and oxalic acid under a variety of carbon and nitrogen regimes and did not contain double-stranded RNA. An understanding of the physiology of this isolate would further our knowledge of decay mechanisms leading to safer preservation protocols.