MICROTUBULES REGULATE THE ORGANIZATION OF ACTIN-FILAMENTS AT THE CORTICAL REGION IN ROOT HAIR-CELLS OF HYDROCHARIS

We studied the mechanism controlling the organization of actin filamen ts (AFs) in Hydrocharis root hair cells, in which reverse fountain str eaming occurs. The distribution of AFs and microtubules (MTs) in root hair cells were analyzed by fluorescence microscopy and electron micro scopy. AFs and MTs were found running in the longitudinal direction of the cell at the cortical region. AFs were observed in the transvacuol ar strand, but not MTs. Ultrastructural studies revealed that AFs and MTs were colocalized and that MTs were closer to the plasma membrane t han AFs. To examine if MTs regulate the organization of AFs, we carrie d out a double inhibitor experiment using cytochalasin B (CB) and prop yzamide, which are inhibitors of AFs and MTs, respectively. CB reversi bly inhibited cytoplasmic streaming while propyzamide alone had no eff ect on it. However, after treatment with both CB and propyzamide, remo val of CB alone did not lead to recovery of cytoplasmic streaming. In these cells, AFs showed a meshwork structure. When propyzamide was als o removed, cytoplasmic streaming and the original organization of AFs were recovered. These results strongly suggest that MTs are responsibl e for the organization of AFs in Hydrocharis root hair cells.