Microinjection of pollen‐specific actin‐depolymerizing factor, ZmADF1, reorientates F‐actin strands in Tradescantia stamen hair cells

Summary Maize actin‐depolymerizing factor (ADF) binds both monomeric and filamentous actin and increases actin dynamics in vitro . To test its effects in vivo , recombinant pollen ADF1 was expressed in bacteria and microinjected into Tradescantia stamen hair cells. Initially, all cytoplasmic streaming ceased and the central, longitudinal transvacuolar strands were disrupted. After 20–45 min, streaming resumed but in the form of conspicuous transverse pathways of movement in the cortex. Staining the actin filaments by a second injection of fluorescein‐conjugated phalloidin showed that the longitudinal actin cables seen in controls had been replaced by a thickening of the transverse cortical arrays, whose orientation matched the new pattern of streaming. Microinjection of rhodamine–tubulin confirmed that the microtubules also formed a transverse cortical array and it is suggested that the spatial cues for re‐modelling the actin after ADF1 injection may be provided by the microtubular system.