Negative phototropism of the creeping shoots in Japanese Ivy, Hedera rhombea

Abstract

We analyzed the relationships between the growth direction of creeping shoot in Japanese ivy( Hedera rhombea) and the light conditions experimentally. As a result, the creeping shoots( ≥10 mm in length) of the ivy clearly showed negative phototropism clearly. The negative phototropism led the shoot horizontally and vertically into the dark space strictly along the negative gradient of spatial light intensity. The growth rate of the shoot decreased according to the reduction of light intensity, but negative phototropism still occurred under the weaker light conditions (20 μmol m-2 s -1). Therefore, negative phototropism in the creeping shoots of this species must be understood as the active response of searching for a dark space instead of the response of avoiding a strong light. When a creeping shoot searches for an effective tree as a climbing support under heterogeneous light conditions such as forest floors, this negative phototropism would provide an ecological function to lead a shoot apex to the most shady tree base which can be a climbing start point.