1. Department of Biological Science and Technology, Science University of Tokyo, 2641 Yamazaki, Noda 278-8510, Japan
2. Mitsui Plant Biotechnology Research Institute, Tsukuba 305, Japan
3. National Institute of Agrobiological Sciences, 2-1-2 Kan-non-dai, Tsukuba 305-8602, Japan
4. Life Science Institute, Mitsui Chemicals, Inc., Mobara 278-0017, Japan