The role of cytoplasmic streaming in symplastic transport

Abstract

The distributing of materials throughout a symplastic domain must involve at least two classes of transport steps: plasmodesmatal and cytoplasmic. To underpin the latter, the most obvious candidate mechanisms are cytoplasmic streaming and diffusion. The thesis will be here advanced that, although both candidates clearly do transport cytoplasmic entities, the cytoplasmic streaming per se is not of primary importance in symplastic transport but that its underlying molecular motor activity (of which the streaming is a readily visible consequence) is . Following brief tutorials on low Reynolds number flow, diffusion, and targeted intracytoplasmic transport, the hypothesis is broached that macromolecular and vesicular transport along actin trackways is both the cause of visible streaming and the essential metabolically driven cytoplasmic step in symplastic transport. The concluding discussion highlights four underdeveloped aspects of the active cytoplasmic step: (i) visualization of the real-time transport of messages and metabolites; (ii) enumeration of the entities trafficked; (iii) elucidation of the routing of the messages and metabolites within the cytoplasm; and (iv) transference of the trafficked entities from cytoplasm into plasmodesmata.

Movement and Remodeling of the Endoplasmic Reticulum in Nondividing Cells of Tobacco Leaves

“…The fact that directional diffusion occurs after BFA treatment helps establish that directional diffusion is not a property of tubules alone. This process of directional diffusion within tubules (near one-dimensional) and cisternae (near two-dimensional) may provide a mechanism whereby proteins and metabolites can be more efficiently transferred through the cell with minimal expenditure of energy at rates that far exceed those of nondirectional diffusion in three dimensions (Adam and Delbruck, 1968;Loverdo et al, 2008;Mirny, 2008;Pickard, 2003).…”

Hydrodynamic flow caused by active transport along cytoskeletal elements

“…In particular, for cytoplasmic streaming in plant cells collective hydrodynamic effects could explain the rapid transport of organelles [7][8][9][10]. Here unidirectional active transport takes place trough cytoplasmic strands.…”

Coupled oscillations of a protein microtubule immersed in cytoplasm: an orthotropic elastic shell modeling

“…This work was possible owing to a recently obtained experimental and numerical body of data coming from several groups and describing a number of physical and structural properties of the microtubule and the cytoplasm [18,19,25,30,33]. A first-order shear deformation shell theory for orthotropic materials was developed for microtubules to predict the coupled frequencies of the microtubule-cytoplasm system.…”

“…We use the Navier-Stokes equations for incompressible fluids in cylindrical coordinates to obtain the cytosol equations of motion. It has been shown by several researchers that the Reynolds number is very low for cytoplasmic streaming, for instance, Re = 10 −3 [25] and the inertia terms in the Navier-Stokes equations are negligible. With these approximations and neglecting the axial motion of the cytosol, the momentum-balance equation for the cytosol motion can be described by the well-known Stokes equations as…”