1. Institute of Genetic Ecology, Tohoku University, Katahira, Aoba-ku, Sendai, 980-8577,1
2. Plant Biotechnology Institute, Ibaraki Agricultural Center, Ago, Iwama, Nishi-Ibaraki, 319-0292,2
3. Department of Plant Physiology, National Institute of Agrobiological Resources, Tsukuba, Ibaraki, 305-8602;3 and
4. School of Agriculture, Ibaraki University, Ami, Ibaraki, 300-0393,4 Japan