Investigating Mechanisms of Cytoplasmic Flow in Hyphal Growth

Cytoplasm within hyphae exhibits a mass flow towards the apical tip. It has been hypothesized that these flows are driven by pressure gradients along the length of the hypha, but the mechanism by which such gradients are established remains unclear. In this study, I explore potential mechanisms for generating pressure gradients and compare them to alternative explanations for cytoplasmic flow within hyphae. Using Particle Image Velocimetry  (PIV) and Mean Squared Displacement (MSD), I measure flow velocities in the hyphae of the water mold Achlya bisexualis. Our analysis reveals that hyphae exhibit plug-like flow with relatively uniform velocity profiles. These flow velocities correlate with hyphal growth rates. When growth is halted via hyperosmotic shock, flow slows and flow polarity is disorganized. In some cases, flow reversal is observed, consistent with the idea that hyperosmotic shock can invert the pressure gradient. It is thought that spatially segregated ion fluxes between the apical and basal regions of the hypha may establish this pressure gradient. I will present models demonstrating the conditions under which differential ion fluxes can generate such gradients, along with experimental data supporting this mechanism and testing the predictions of these models.