Effects of heavy-ion and laser microbeam irradiation on root hydrotropism of

Miyazawa, Yutaka*; Sakashita, Tetsuya; Negishi, Hiroshi*; Kobayashi, Akie*; Oba, Atsushi*; Kaneyasu, Tomoko*; Morohashi, Keita*; Takahashi, Akiko*; Kakizaki, Takehiko*; Funayama, Tomoo; Hamada, Nobuyuki*; Wada, Seiichi*; Kobayashi, Yasuhiko; Fujii, Nobuharu*; Takahashi, Hideyuki*

We examined the function of root cap and elongation zone cells in root hydrotropism by nondestructive cell inactivation using heavy-ion microbeam irradiation. Systemic heavy-ion irradiation inactivated de novo indole acetic acid 5 gene expression. Local irradiation of the elongation zone significantly suppressed the development of hydrotropic curvature, whereas local irradiation of the columella cells did not. However, laser ablation confirmed that columella cells are indispensable for hydrotropism. Our results indicate that both the root cap and elongation zone have indispensable and functionally distinct roles in root hydrotropism, and that in the elongation zone, de novo gene expressions, including auxin-responsible gene expression, is required for hydrotropism, whereas in columella cells, it is not.