Norlignan biosynthesis in Asparagus officinalis L.: the norlignan originates from two non-identical phenylpropane unitsParts of this work were presented at the 50th annual meeting of the Japan Wood Research Society, April 3, 2000, Kyoto, Japan; the 45th Lignin Symposium, October 26, 2000, Matsuyama, Japan; and the annual meeting of the Japan Society for Bioscience, Biotechnology, and Agrochemistry, March 24, 2001, Kyoto, Japan.