Figure 4

Nuclear lobes are bound by the ER membrane and contain ER lumen contents. A hypocotyl of the ER membrane marker line Q4 was wounded and imaged at 2-minute intervals by confocal microscopy. The simultaneous contraction and lobing of the nucleus are evident as a separation of the nuclear envelope. (A) 3D reconstruction of the contracting nucleus made with a brightest-point reconstruction of the acquired data set. (B) The same data set as in Fig. 4A at a single optical section through the mid-plane of the contracting nucleus, illuminating the double membrane structure (pointed to by arrows) and its separation. (C) A single optical section through the contracted nucleus shows propidium iodide staining (shown in red) of the interior, demonstrating that the nuclear lumen is interior to the lobes. (D, E) Hypocotyls of a line expressing the ER-lumenal GFP marker mGFP5 were wounded. Shown are contracting epidermal nuclei (white arrows) from two independent wound experiments using mGFP5 approximately 10 min after wounding. The inter-lobal space contains mGFP5 label (red arrows), indicating that this compartment is contiguous with the lumen of the ER. GFP fluorescence is shown in green and propidium iodide in red. Scale bars = 10 μm.