1-Aminocyclopropane-1-carboxylic acid (ACC)-induced reorientation of cortical microtubules is accompanied by a transient increase in the transcript levels of γ-tubulin complex and katanin genes in azuki bean epicotyls

The effects of 1-aminocyclopropane-1-carboxylic acid (ACC), the immediate precursor of ethylene, on growth, orientation of cortical microtubules, and the transcript levels of γ-tubulin complex (VaTUG and VaGCP3) and katanin (VaKTN1) genes in azuki bean (Vigna angularis) epicotyls were examined. ACC inhibited elongation growth and stimulated lateral growth of epicotyls dose dependently. It also reduced the percentage of cells with transverse microtubules and increased the percentage of cells with longitudinal microtubules. A significant change in elongation and lateral growth was detected within 1 and 1.5 h after the start of 10−5 M ACC treatment, respectively. On the other hand, the reorientation of cortical microtubules from transverse to longitudinal direction began within 0.5 h, and continued until 2 h after the start of ACC treatment. ACC at 10−5 M increased the transcript level of VaTUG, VaGCP3 and VaKTN1 within 0.5 h, and the levels of VaTUG and VaGCP3 became maximum at 1 h and that of VaKTN1 at 1.5 h, followed by a decrease to the control level. These results suggest that ACC transiently increases the transcript levels of γ-tubulin complex and katanin genes, which may facilitate reorientation of cortical microtubules and modification of growth anisotropy from elongation to lateral growth in azuki bean epicotyls.