Actin cytoskeleton is responsible for the change of cytoplasmic organization in root hair cells induced by a protein phosphatase inhibitor, calyculinA

In root hair cells of Limnobium stoloniferum, a protein phospha;ase inhibit or, calyculin A (CA), at concentrations higher than 50 nM inhibits cytoplas mic streaming and induces remarkable morphological changes in the cytoplasm : the transvacuolar strands disperse and spherical cytoplasmic bodies emerg e. The mechanism of the morphological changes of the cytoplasm induced by C A was studied by pharmacological analyses. The formation of spherical bodie s in cells treated with CA was suppressed by the actin-depolymerizing and - fragmenting drugs latrunculin B and cytochalasin D at concentrations higher than 100 nM and 5 mu M, respectively. In contrast, 100 mu M propyzamide, a microtubule-depolymerizing drug, did not affect the formation of spherical bodies by CA. Interestingly, 60 mM 2,3-butanedione monoxime, an inhibitor of myosin, also suppressed the CA-induced formation of cytoplasmic spherica l bodies. These results indicate that the actin cytoskeleton is intimately involved in the morphological changes of the cytoplasm induced by CA.