1. Centre de Recherches sur les Macromolécules Végétales, CNRS, BP 53, 38041 Grenoble Cédex 9, affiliated with the Joseph Fourier University of Grenoble, France, Laboratory of Structural Biopolymers, Department of Biomaterial Sciences, Graduate School of Agriculture and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113, Japan, and INSU CNRS Roscoff, URM7 IFREMER, Université Pierre et Marie Curie, 7 Quai Saint Bernard, 75252 Paris, Cédex 05, France