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Fungi Pore size Cell wall void volume Wood decay Lignin Cellulose Hemicellulose Simultaneous rot Phancrochucte chrysosporium «Eunls. SummaryThe purpose of this study was to examine changes in cell wall void (pore) volume and pore sixe distribution in swcctgum wood during decay by a white-rot fungus, Phanerochaete clirysosporium 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. Swectgum (LiquUkimbur styrucifluu L.) wood blocks were decayed by Phunerochtiett: chrysosporium Burds. in soil-block cultures. Lignin, cellulose and licmiccllulose 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 A). In white-rot decayed wood, cell wall void volume increased to 0.6 ml -g ' at 40% weight loss, and maximum pore diameter increased to more than 5 nm (50 A). Most of the cell wall void volume increase resulted from the creation of pores of 2 to 5 nm (20 to 50 A) 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 30Ä) may gain access to considerable new cell void volume.

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