DIFFERENTIAL CYTOPLASM-PLASMA MEMBRANE-CELL WALL ADHESION PATTERNS AND THEIR RELATIONSHIPS TO HYPHAL TIP GROWTH AND ORGANELLE MOTILITY

Plasmolysis of hyphae of the oomycetes Saprolegnia ferax and Achlya am bisexualis and the ascomycete Neurospora crassa produced abundant cyto plasmic strands between the retracted cytoplasm and punctate adhesions of the plasma membrane to the cell wall. These strands formed through out the length of mature hyphae and are the first demonstration of Hec htian strands in hyphae. In contrast to similar strands in various pla nt cells, the strands in Saprolegnia lacked endoplasmic reticulum but contained F-actin, suggesting similarity between their adhesion sites and focal contacts in animal cells. However, strand adhesion to the wa ll was insensitive to RGD-containing peptides, suggesting that the tra ns-membrane adhesion molecules differ from animal integrins. The patte rn of plasma membrane-cell wall adhesion varied in different zones alo ng hyphae. with broad, irregular connections in the extreme apex, unif orm and continuous connection in a transition zone, end small, punctat e adhesions in the mature subapical zone, suggesting differential func tions in these different regions. The apical adhesions are important i n tip growth, as diverse inhibitors induced concomitant changes in hyp hal growth and the adhesions in the apical and transition zones. Plasm olysis also induced cytoplasmic migrations throughout hyphae. Such mig rations were dominated by the central cytoplasm, and produced distorte d organelles which spanned central and peripheral cytoplasm, thus supp orting the idea that the adhesions in mature zones of hyphae anchor th e peripheral cytoplasm and facilitate cytoplasmic and organelle migrat ions.