CHANGES IN THE SIZE AND VOLUME OF PORES IN SWEETGUM WOOD DURING SIMULTANEOUS ROT BY PHANEROCHAETE-CHRYSOSPORIUM BURDS

The purpose of this study was to examine changes in cell wall void (pore) volume and pore size distribution in sweetgum wood during decay by a white-rot fungus, Phanerochaete chrysosporium Burds. Results of the study may provide quantitative answers to questions regarding the accessibility of degradative proteins to their respective substrates within the cell wall. Sweetgum (Liquidambar styraeiflua L.) wood blocks were decayed by Phanerochaete chrysosporium Burds. in soil-block cultures. Lignin, cellulose and hemicellulose were removed at approximately equal rates with progression of decay. Decay was terminated at various weight losses, and the pore volumes available to probes of various molecular weight and diameter were determined by the solute exclusion technique. The cell wall void volume in sound sweetgum wood was 0.35 ml . g-1 and the maximum pore diameter, 2 nm (20 angstrom). In white-rot decayed wood, cell wall void volume increased to 0.6 ml . g-1 at 40% weight loss, and maximum pore diameter increased to more than 5 nm (50 angstrom). Most of the cell wall void volume increase resulted from the creation of pores of 2 to 5 nm (20 to 50 angstrom) diameter. Assuming a model in which the cell wall is built of microfibrils laterally associated to form lamellae, we conclude that ligninolytic enzymes are expected to penetrate only a small fraction of new cell wall void volume, even after extensive decay, whereas small enzymes of 2 to 3 nm (20 to 30 angstrom) may gain access to considerable new cell void volume.