Involvement of cortical microtubules in plastic extension regulated by gibberellin in Lemna minor root

We aimed to analyze the theological characteristics during elongation of th e root segments in Lemna minor. The elastic component of segment elongation (EC) increased for the first 6 h, and then almost stopped. However, the pl astic component of the segment elongation (PC) began to rapidly increase fr om 6 h onwards, Uniconazole-P, a gibberellin biosynthesis inhibitor, inhibi ted the total elongation of root segments (TE), and this inhibition was mai nly caused by suppression of the rapid increase in the PC after 6 h, Concom itant with this inhibition, the cortical microtubule (CMT) array within roo t epidermal cells became disorganized in the presence of uniconazole-P from 6 h onwards, Adding GA(3) abolished the inhibition of TE by uniconazole-P treatment, and this recovery was caused not by the increase in the EC but b y an increase in the PC. Furthermore, the CMT arrays also recovered their c haracteristic organization in the presence of GA(3). These findings suggest that endogenous gibberellin accelerates TE by activating the PC via contro l of CMT arrays. This conclusion is also supported by theological analysis where propyzamide was used to disrupt microtubules. We suggest that endogen ous gibberellin controls the PC via its influence over the transverse arran gement of CMTs.