Inhibitory effect of colchicine on growth and gravitropic responses in Arabidopsis root was explored to find whether there was an involvement of ethylene production. It has been known that cytoskeleton components are implicated in sedimentation of statoliths to respond to gravitropism and growth. The root growth was inhibited by 25% and 40% over control for 8 hr treatment of colchicine at a concentration of 10-5 M and 10-7 M, respectively. The roots treated with colchicine at the concentration of 10-7 M showed the same pattern as control in 3 hr, however, gravitropic response was decreased in the next 5 hr. The colchicine treatment at the concentration of 10-5 M inhibited the gravitropic response resulting in 60° of curvature. In order to better understand the role of colchicine, the production of ethylene was measured with and without the treatment of colchicine. Colchicine increased the ethylene production by 20% when compared to control via the activation of ACC oxidase and ACC synthase activity. These results suggest that the inhibition of the growth and gravitropic responses of Arabidopsis roots by the treatment of colchicine could be attributed to the rearrangement of microtubule, and increase of ethylene production.

To develop a strong root-specific gene expression system, six gene promoters were investigated by using transgenic Arabidopsis and a GUS:GFP reporter gene. These promoters were initially selected from Arabidopsis genes which are specifically expressed only in roots, based on the TIGR information. The GUS activity of these promoters was measured in several tissues of Arabidopsis by using both histochemical and fluorimetric GUS assays. The results showed that the activity of these promoters was strongly detected only roots. This was also confirmed by RT-PCR analysis. Therefore, these six promoters could be used for utilization of a root-specific expression of target genes.