1. Graduate School of Agricultural and Life Science, The University of Tokyo, Yayoi, Tokyo 113-8256, Japan; European Synchrotron Radiation Facility, B.P. 220, 38043 Grenoble Cedex, France; and Centre de Recherches sur les Macromolecules Végétales, CNRS, affiliated with the Joseph Fourier University of Grenoble, BP 53, 38041 Grenoble Cedex 9, France