  Many cells exhibit large-scale active circulation of their entire fluid
contents, a process termed cytoplasmic streaming. This phenomenon is
particularly prevalent in plant cells, often presenting strikingly regimented
flow patterns. The driving mechanism in such cells is known: myosin-coated
organelles entrain cytoplasm as they process along actin filament bundles fixed
at the periphery. Still unknown, however, is the developmental process which
constructs the well-ordered actin configurations required for coherent
cell-scale flow. Previous experimental works on streaming regeneration in cells
of Characean algae, whose longitudinal flow is perhaps the most regimented of
all, hint at an autonomous process of microfilament self-organization driving
the formation of streaming patterns during morphogenesis. Working from first
principles, we propose a robust model of streaming emergence that combines
motor dynamics with both micro- and macroscopic hydrodynamics to explain how
several independent processes, each ineffectual on its own, can reinforce to
ultimately develop the patterns of streaming observed in the Characeae and
other streaming species.
