(98e) Asymmetric Cytoplasmic Streaming Across Septal Pore in Fungal Hyphae

We investigate the phenomenon of cytoplasmic streaming across a septal pore in the filamentous fungi, Neurospora crassa. Experimentally, we found that the flow profile across some septal pores in mature hyphae to be asymmetric, where the inlet flow resembles a long and narrow converging funnel in contrast with the broad diverging funnel at the outlet. The emergence of asymmetric flow behavior is somewhat surprising, since the Reynolds numbers are vanishingly small. To this, we propose and discuss two hypotheses. One considers the accumulation of organelles and other cytoplasmic deposits before the cross wall, which can be modeled as a porous region using Darcy-Brinkmann equations. With a perfectly impermeable deposition region, fluid is displaced towards the centerline so that the entrance bulk flow in the core approaches that of a converging pipe.  In practice, however, it is difficult to assess the extent of deposition and its effect on the flow. Another approach considers the non-Newtonian behavior of the cytoplasmic fluid, where the stretching of semi-rigid polymers could lead to extensional flow at the accelerating inlet side, and relaxation of polymers on the decelerating outlet side. This proposition appears simpler in requirements, but such anisotropic flow behavior in cytoplasmic fluids is neither widely observed, nor well-understood. Since both hypotheses are not mutually exclusive, the actual phenomena may in fact be attributed to some combination of the two effects. This work has implications in cytoplasmic streaming processes in fungi, as well as the transport of suspensions through a microfluidic orifice.