1. Department of Physics, The Norwegian University of Science and Technology, NTNU, NO-7491 Trondheim, Norway, Department of Biomaterials Science, Graduate School of Agricultural and Life Science, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan, and Centre de Recherches sur les Macromolecules Vegetales (Affiliated with Joseph Fourier University of Grenoble), C.N.R.S. B.P. 53, 38401, Grenoble Cedex 9, France