Lifeact-mEGFP in Plant Cells advantage of this to examine branch formation in a chloronemal cell (Figure 8A). As the branch begins to emerge, a focal point of actin develops at the tip. Behind this, the actin caging around the chloroplasts is clearly evident. This focal point increases in size as the branch lengthens, resembling the apical actin structure observed in chloronemal cells at the apex of a filament. Finally, a phragmoplast forms at the cell junction (Figure 8A). We collected z-stacks of subapical caulonemal cells. Not surprisingly, the cages around chloroplasts are less prominent as these cells have many fewer chloroplasts. However longitudinal cortical filaments are evident as is a striking accumulation of Lifeact-mEGFP at the cell plate. We also examined cells in gametophore leaflets. Labeling of cortical microfilaments is apparent as is caging around the chloroplasts. Taken together these images demonstrate that Lifeact-mEGFP enables live imaging of actin in a variety of cell types. Conclusions In this report we use Lifeact-mEGFP as a live cell probe for actin in the moss Physcomitrella patens as well as in pollen from two species, Lilium formasanum and Nicotiana tobaccum. Our data indicate that Lifeact-mEGFP possesses significant advantages in tip growing cells over other commonly used live-cell probes. At Figure 8. Maximal projections of Lifeact-mEGFP labeling in moss subapical protonemal and gametophore cells. (A) shows a sequence of maximal projections of z-stacks documenting branch emergence from a moss chloronemal cell expressing Lifeact-mEGFP. (B) shows representative subapical caulonemal cells expressing Lifeact-mEGFP. (C) Representative gametophores cells expressing Lifeact-mEGFP. Bars are 5 mm. doi:10.1371/journal.pone.0005744.g008 PLoS ONE | www.plosone.org 11 May 2009 | Volume 4 | Issue 5 | e5744