POLYMERIZATION OF ACTIN FROM MAIZE POLLEN

Here we describe the in vitro polymerization of actin from maize (Zea mays) pollen. The purified actin from maize pollen reported in our pre vious paper (X. Liu, L.F. Yen [1992] Plant Physiol 99: 1151-1155) is b iologically active. In the presence of ATP, KCl, and MgCl2 the purifie d pollen actin polymerized into filaments. During polymerization the s pectra of absorbance at 232 nm increased gradually. Polymerization of pollen actin was evidently accompanied by an increase in viscosity of the pollen actin solution. Also, the specific viscosity of pollen F-ac tin increased in a concentration-dependent manner. The ultraviolet dif ference spectrum of pollen actin is very similar to that of rabbit mus cle actin. The activity of myosin ATPase from rabbit muscle was activa ted 7-fold by the polymerized pollen actin (F-actin). The actin filame nts were visualized under the electron microscope as doubly wound stra nds of 7 nm diameter. If cytochalasin B was added before staining, no actin filaments were observed. When actin filaments were treated with rabbit heavy meromyosin, the actin filaments were decorated with an ar rowhead structure. These results imply that there is much similarity b etween pollen and muscle actin.