A panel structure for a demountable partition system usable for dividing a room or for forming rooms and/or corridors or other structures, the panel structure having two opposite major faces and in use being positioned in a generally upright orientation with other such panel structures of the system, in which there are provided one or more rolling elements movable using a gearbox mechanism between an extended, ground-contacting position, and a retracted position within the panel structure, wherein the rolling elements and the gearbox mechanism are disposed in relation to the panel structure to preserve an operating characteristic of the panel structure.