Abstract
Phototropic response is the result of differential growth on the two sides of the elongating shoot, which can be explained by the asymmetrical IAA distribution. Using detached coleoptile segment, we confirmed first positive phototropism. To reveal the region causing phototropic curvature, effects of partial light irradiation on the curvature were tested. The result showed the photo-stimulus was received within the apical 2-mm region. IAA redistribution was established at 3-mm tip after 20 min of blue light, and then the asymmetric distribution was transmitted to lower region. These result indicated that this region harbors some factor(s) responsible for photosensing and lateral IAA transport. In the present study, we found that NPH3- and PGP-like genes were exclusively expressed in the tip 0-2 mm region, whereas PHOT1 and ZmPIN1s were expressed relatively evenly along the coleoptile. These results suggest that the NPH3- and PGP-like gene products have a key role in photo-signal transduction and regulation of the direction of IAA transport after blue light perception by phot1 at the very tip region of maize coleoptile.
