1. Division of Applied Bioscience, Graduate School of Agriculture Kyoto University Kitashirakawa Oiwake‐cho, Sakyo‐ku, Kyoto 606‐8502 Japan
2. Department of Anatomy and Cell Biology Wakayama Medical University 580 Mikazura, Wakayama‐shi 641‐0011 Japan
3. Division of Applied Life Sciences, Graduate School of Agriculture Kyoto University Kitashirakawa Oiwake‐cho, Sakyo‐ku, Kyoto 606‐8502 Japan