1. Contribution from the Department of Biomaterial Sciences, Graduate School of Agriculture and Life Science, the University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan, Wood Research Institute, Kyoto University, Uji, Kyoto 611-0011, Japan, Centre de Recherches sur les Macromolécules Végétales, CNRS, affiliated with the Joseph Fourier University of Grenoble, BP 53, 38041 Grenoble Cedex 9, France, and Bioscience Division, Los Alamos National Laboratory, Los Alamos, New Mexico 87545