Negative Phototropism of Chlorophytum comosum Roots and Their Mechanisms

The aerial roots of Chlorophytum comosum were grown hydroponically,allowing us to study the performance and mechanism of negative phototropism. The results of this study were as follows. All the adventitious roots and their branch roots bent away from light with a maximum curvature of approximately 88.5°. Blue-violet light prominently induced negative phototropism while red light had no effect. The root cap was the site of photo perception. Roots with shaded or divested root caps exposed to unilateral light showed no negative phototropism,but resumed their original characteristics when the shade was removed or when new root caps grew. The curvature increased when the light intensity ranged 0–110 μmol·m^(-2)·s^(-1). The negative phototropism curvature could be promoted by exogenous CaCl_2 but was inhibited by exogenous LaCl_3; exogenous CaCl_2 could reduce the inhibitory effect of LaCl_3. Unilateral light induced the horizontal transport of IAA from the irradiated side to the shaded side,resulting in an unequal distribution of IAA in both the sides,leading to negative phototropism. The horizontal transport of IAA was promoted by exogenous Ca^(2+) but inhibited by exogenous La^(3+).