1. Department of Botany, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
2. National Institute for Basic Biology, Okazaki 444-8585, Japan
3. College of Integrated Arts and Sciences, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
4. Department of Biological Science, Graduate School of Science, University of Tokyo, Tokyo 113-8656, Japan