In the majority of plant cells the endoplasmic reticulum (ER) exists predominantly in the form of a cortical network of tubules with small cisternae.This network is dynamic, constantly changing shape, with new tubules growing a shrinking.We have shown that this movement is dependent on the actin network and driven by myosin motors.By mapping the distribution of ER tubules and cisternae with time, it can be seen that there are areas of ER that are static and others which are more mobile, and the network appears to be anchored at the cell cortex by a number of punctate anchor points.We have long suspected that Golgi bodies are involved somehow in the dynamics of the ER network as they are motile over the ER network and directional movement is linked to ER movement.By the application of infrared laser optical traps to individual Golgi bodies within living arabidopsis leaf cells, we have shown that Golgi bodies can be micromanipulated to reveal their association with the ER.Golgi bodies appear to be physically attached to ER tubules and displacement of individual Golgi bodies by moving the laser trap results in the rapid growth of any attached ER tubule.Thus, the ER network can be remodelled in living cells simply by movement of laser trapped Golgi dragging new ER tubules through the cytoplasm and new ER anchor sites can be established.Trapped Golgi ripped off the ER are "sticky" and can be docked on to and attached to ER tubules.Mutation of a putative tethering factor AtCASP loosens the link between the Golgi and the ER.Shaping of the tubular ER network is likely mediated by the reticulons, a recently described family of membrane proteins that have been shown to affect mammalian and yeast ER tubule formation.They are ubiquitous in eukaryotes and share a carboxy-terminal homology domain and two large hydrophobic regions.It is thought that these regions are transmembrane domains forming hairpins within the lipid bilayer with a wedge-like topology which induces curvature on the membrane.Little is known about the presence or function of plant reticulons but when fused to fluorescent proteins a number of them locate predominantly to tubular ER or the curved rims of cisternal ER in both tobacco leaf cells and Arabidopsis plants.When over-expressed along-side soluble ER markers, reticulons induce severe constriction of the ER lumen and reduce the diffusion of soluble proteins in the lumen.However, Golgi dynamics and secretion appear unperturbed.We have dissected the minimal structural RTN domain required to which reticulons may be targeted, and to constrict the tubular ER (number and length of TMDs) and confirmed the membrane topology of the proteins.