Possible involvement of protein phosphorylation in the regulation of cytoplasmic organization and streaming in root hair cells as revealed by a protein phosphatase inhibitor, calyculin A

The effects of a protein phosphatase inhibitor, calyculin A (CA), on cytopl asmic streaming and cytoplasmic organization were examined in root hair cel ls of Limnobium stoloniferum. CA at concentrations higher than 50 nM inhibi ted cytoplasmic streaming and also induced remarkable morphological changes in the cyto plasm. The transvacuolar strands, in which actin filament bund les were oriented parallel to the long axis, disappeared and spherical cyto plasmic bodies emerged in the CA-treated cells. In these spherical bodies, actin filaments were present and the spherical bodies were connected to eac h other by thin strands of actin filaments. Upon CA removal, transvacuolar strands, in which actin filament bundles were aligned, and cytoplasmic stre aming reappeared. A nonselective inhibitor for protein kinases, K-252a, del ayed the inhibitory effect of CA on cytoplasmic streaming and suppressed th e CA-induced formation of the spherical bodies. From these results, it is s uggested that phosphatases sensitive to CA regulate cytoplasmic streaming a nd are involved in the organization of the cytoplasm in root hair cells.