1. Biological Resources Division, Japan International Research Center for Agricultural Science (JIRCAS), Ministry of Agriculture, Forestry and Fisheries, 1-2 Oowashi, Tsukuba, Ibaraki 305, Japan
2. Laboratory of Plant Molecular Biology, Institute of Physical and Chemical Research (RIKEN), Tsukuba Life Science Center, 3-1-1 Koyadai, Tsukuba, Ibaraki 305, Japan