Phys. Rev. Lett. 101, 178102 (2008)

Credit: J.-W. VAN DE MEENT, M. POLIN, R. E. GOLDSTEIN/UNIV. CAMBRIDGE

The tubular cells of the aquatic plant Chara corallina are several centimetres long and about 1 millimetre wide — too big for diffusion to effectively disperse nutrients within them, but too small for the pumping circulatory systems of large organisms. So the cytoplasm of such a cell circulates by advection. This is driven by the movement of myosin motor proteins along 'tracks' of the filamentous protein actin on the cell's inner walls. But the details of how this works have been unclear.

Jan-Willem van de Meent and his colleagues at the University of Cambridge, UK, now present a model in which advection by the myosin 'conveyor belts' generates two counterflowing, helically entwined vortices. These mix and homogenize solutes much faster than would diffusion. The idea could be copied in microfluidic systems, in which generating rapid mixing is difficult.