THE PLANT ONCOGENE ROLB ALTERS BINDING OF AUXIN TO PLANT-CELL MEMBRANES

We measured auxin-binding capacity of the membrane preparations from tobacco cells transformed by rolB as compared to untransformed controls. In the transformed cells, the overall auxin-binding activity is severalfold enhanced through an increase in a binding activity removable from the membranes at 0.5 M salt, while the binding activity still attached to the membranes after salt washes remains unchanged. Antibodies against the 22 kDa maize auxin binding protein (ABP) depress most of the membrane-attached binding activity in both normal and rolB-transformed cells, while they do not affect the salt-washable binding activity. In contrast, antibodies against the RolB protein prevent completely binding of auxin to the latter activity in both normal and transformed cells, while substantially unaffecting the membrane-associated binding. These results point to the presence, in untransformed membranes, of an auxin-binding activity associated with a protein immunologically related to RolB. This activity is much increased in rolB cells. In contrast, the auxin-binding protein analogous to maize ABP present in tobacco membranes does not increase in the ro[B-transformed cells.