An investigation into plasmolysis in the oomycete Achlya bisexualis reveals that membrane-wall attachment points are sensitive to peptides containing the sequence RGD and that cell wall deposition can occur despite retraction of the protoplast.

The structure and function of membrane-wall attachment sites in walled cells, and how these relate to animal focal adhesions, is an area that is poorly understood. In view of this, we investigated how membrane-wall attachments that form upon plasmolysis, respond to peptides that disrupt animal focal adhesions. The degree of cytoplasmic disruption during plasmolysis was also investigated. Upon hyperosmotic challenge, the protoplast in hyphae of the oomycete Achlya bisexualis typically retracted incompletely due to membrane-wall attachments. The inclusion, in the plasmolysing solution, of peptides containing the sequence RGD disrupted these attachments in a dose-dependent manner. In some hyphae, protoplast retraction stopped temporarily at attachment points - upon resumption of retraction, material was left that traced the outline of the static protoplast. Staining of this material with fluorescence brightener indicated the presence of cellulose, which suggests that wall deposition was able to occur despite plasmolysis. The F-actin cytoskeleton was disrupted during plasmolysis; peripheral F-actin staining was observed, but there was no distinct F-actin cap; staining was more diffuse; and there were fewer plaques compared with nonplasmolysed hyphae. Our data indicate that membrane-wall attachment points are sensitive to RGD-containing peptides and that wall deposition continues despite protoplast retraction and F-actin disruption.