Abstract:The crude extracts of pollen tubes, like other nonmuscle ceils, showed gelation at Iow Ga2+ concentrations and ATP-dependent contraction at higher Ga2+ concentrations. The contracted cytoplasmic clots contained a lot of filaments which were mainly composed of actin, myosin, 105 kD, 67 kD, 48 kD, 38 kD, 34 kD and 28 kD proteins. It is likely that Ca2+ are able to mediate tranformation of acfin from a less ordered state to a more oriented filaments, which interact with actin-binding proteins to form the filamentous network, thus to induce the gel formation of cytoplasm, to regulate the interaction of actin and myosin which transform the chemical energy of ATP into mechanical work of contractile movement of cytoplasm.