PROBING THE PLANT ACTIN CYTOSKELETON DURING CYTOKINESIS AND INTERPHASE BY PROFILIN MICROINJECTION

We have examined the cytological effects of microinjecting recombinant birch profilin in dividing and interphase stamen hair cells of Trades cantia virginiana. Microinjection of profilin at anaphase and telophas e led to a marked effect on cytokinesis; cell plate formation was ofte n delayed, blocked, or completely inhibited, In addition, the initial appearance of the cell plate was wrinkled, thin, and sometimes fragmen ted. Injection of profilin at interphase caused a thinning or the coll apse of cytoplasmic strands and a retardation or inhibition of cytopla smic streaming in a dose-dependent manner. Confocal laser scanning mic roscopy of rhodamine-phalloidin staining in vivo revealed that high le vels of microinjected profilin induced a degradation of the actin cyto skeleton in the phragmoplast, the perinuclear zone, and the cytoplasmi c strands, However, some cortical actin filaments remained intact, The data demonstrate that profilin has the ability to act as a regulator of actin-dependent events and that centrally located actin filaments a re more sensitive to microinjected profilin than are cortical actin fi laments. These results add new evidence supporting the hypothesis that actin filaments play a crucial role in the formation of the cell plat e and provide mechanical support for the cytoplasmic strands in interp hase cells.