The property and function of tubulin-like protein which is integrated in membrane systems of higher plants

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When the segments of azuki bean were incubated with 3-indoleacetic acid (IAA) plus gibberellin A_3 (GA_3), one isoform of a-tubulin, which was speculated to be integrated in membraneous fraction, was found to disappear after 4h.6-Dimethylaminopurine (6-DMAP) prevented not only the disappearance of the ab but also simulataneously prevented the GA_3-induced promotion of elongation.However, purified plasma membrane contained tubulin which did not disappeare after treatment with hormones ans showed unique behavior on 2-D PAGE.Such tubulin was revealed to be integrated in characteristic ring-shaped structures by immunoelectron microscopic observation. The size of the ring-shaped structures was about 30 nm in diameter and resembled to that of terminal complexes.In fact, the formation of abundant filamentous structures of polysaccharide occurred in the preparations which contained ring-shaped structures by the incubation with UDP-glucose in the presence of Ca^<2+>. Although most filaments were b-1,3-glucan, the minor stiff filaments which remained after treatment with b-1,3-glucanase were speculated to be cellulose. Tubulin which disappeare after the treatment with hormone was found in vacuolar membrane. Tubulin in vacuolar membrane was speculated to be associated with 28 KDa protein depending on the presence of divalent cation.