A pressure gradient facilitates mass flow in the oomycete Achlya bisexualis

Abstract

We have used a single cell pressure probe and observed movement of microinjected oil droplets to investigate mass flow in the oomycete Achlya bisexualis. To facilitate these experiments, split Petri dishes that had media containing different sorbitol concentrations (and hence a different osmotic potential) on each side of the dish were inoculated with a single zoospore. An initial germ tube grew out from this and formed a mycelium that extended over both sides of the Petri dish. Hyphae growing on the 0 M sorbitol side of the dish had a mean turgor (¡SEM) of 0.53¡0.03 MPa (n513) and on the 0.3 M sorbitol side had a mean turgor (¡SEM) of 0.3¡0.027 MPa (n59). Oil droplets that had been microinjected into the hyphae moved towards the lower turgor area of the mycelia (i.e. retrograde movement when microinjected into hyphae on the 0 M sorbitol side of the split Petri dish and anterograde movement when microinjected into hyphae on the 0.3 M sorbitol side of the Petri dish). In contrast, the movement of small refractile vesicles occurred in both directions irrespective of the pressure gradient. Experiments with neutral red indicate that the dye is able to move through the mycelia from one side of a split Petri dish to the other, suggesting that there is no compartmentation. This study shows that hyphae that are part of the same mycelia can have different turgor pressures and that this pressure gradient can drive mass flow.

An elastomeric micropillar platform for the study of protrusive forces in hyphal invasion

“…Growth rates of oomycetes and fungi can be variable, typically ranging from 1 -10 µm/min 40 ). For the isolate of A. bisexualis used in the current study, rates around 6-8 µm/min have been previously reported 41 , which is consistent with those observed on our platform.…”

A Monolithic Polydimethylsiloxane Platform for Zoospore Capture, Germination and Single Hypha Force Sensing

“…A. bisexualis zoospores were produced through a starvation cycle of A. bisexualis [16]. In brief, six inoculum plugs from a fresh culture growing edge of A. bisexualis were evenly spread around on a nappy liner, which was placed on peptoneyeastglucose (PYG) agar Petrie dish.…”

“…Then it was swirled on an orbital shaker at 150 rpm for 24 hours at 26 °C. The PYG broth in the flask was exchanged with a mineral salt solution [16] six times and swirled again at 150 rpm at 26 °C overnight. The content of the flask was filtered by sterile Kimwipes and vortexed for 10 s to collect fully developed zoosporangia and released zoospores in solution.…”

What actually is the Münch hypothesis? A short history of assimilate transport by mass flow

“…Unless Pfeffer's mechanism is a fallacy we all fell victim to, hyphae of fungi with perforated septa are free‐living sieve tubes, biophysically speaking. Osmotically induced mass flow in such hyphae is an established fact (Ternetz ; Jennings ; Abadeh and Lew ; Muralidhar et al ), but phloem and fungal physiologists seem to enjoy limited scientific interaction, to judge from the reference lists in their papers. We feel that the potential conceptual and methodological benefits that can result from occasional shifts of our focus from the phloem of higher plants to other systems showing translocation by Pfeffer's mechanism might be underestimated.…”