Immunolocalization of a purified xylanase during hydrolysis of wheat straw stems

Hydrolysis of wheat stems and delignified wheat stems with a purified 20.7 kDa xylanase (EC 3.2.1.8) isolated from a Bacillus sp. yielded 18% and 70% of xylans, respectively. In order to evaluate the accessibility of the xylans and the extent of diffusion of the xylanase in wheat stems, antixylan and antixylanase polyclonal antibodies in conjunction with immunogold labeling and microscopic studies were used on stem fragments degraded by the xylanase. After 30 min of hydrolysis, the labeling of the xylanase was abundant for both lignified and delignified stems and occurred within all cell walls, demonstrating a fast penetration of xylanase in stem fragments. However, the distribution of immunolabel differed between the two types of straw. Xylanase was unevenly distributed in nondelignified straw, especially around the lumen side of cell walls and often grouped in clusters but homogeneous within delignified straw. Localization of xylans in both stem fragments showed that xylans were distributed homogeneously within the entire cell walls. These results indicated that xylans were accessible to the xylanase. The presence of lignins did not prevent, but modulated, the diffusion of the xylanase into stem fragments.