1. Department of Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113, Japan
2. Department of Biology, Faculty of Science, Kyushu University, Fukuoka 812-81, Japan
3. Department of Chemical and Biological Sciences, Japan Women’s University, Mejirodai, Tokyo 112, Japan
4. Division of Biological Science, Graduate School of Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-01, Japan
5. Department of Plant Science, Graduate School of Science, Kyoto University, Kitashirakawa-Oiwake-cho, Sakyo-ku, Kyoto 606-01, Japan