Abstract
Active phototropic bending of radially growing woody stems which have finished elongation has not been documented, while negative gravitropic bending is known. Firstly, we examined existence of active phototropic bending in woody stems and its bending mechanism. We inclined 1-year-old Quercus crispula seedlings and unilaterally irradiated them perpendicular to a vertical plane running parallel to the inclination azimuth to analyze the active phototropic bending separately from negative gravitropic bending and deflection caused by shoot's own weight. One-year-old stems significantly bent with asymmetrical formation of tension wood toward the light source. It is demonstrated that woody stems bend through phototropism with contribution of tension wood formation. Secondly, we examined photoreceptive site in the active phototropic bending. Seedlings were artificially inclined toward south, and east side of 1-year-old stems were masked with aluminum foil. The 1-year-old stems significantly bent toward west. Woody stem itself is shown to contribute photoreception in phototropic bending.
