Immunolocalization of myosin in intact and wounded cells of the green alga Ernodesmis verticillata (Kützing) Borgesen.

Myosin localization was examined in the coenocytic green alga E. verticillata using indirect immunofluorescence microscopy. A polyclonal antibody affinity-purified against the heavy chain of slime-mold myosin recognizes a 220000 to 230000 Mr protein that electrophoretically migrates slightly behind rabbit myosin. A second polypeptide of 85000 Mr is also consistently detected in immunoblots, indicating that two forms of myosin-like proteins may be present in these cells. In intact cells, myosin immunofluorescence is present on the chloroplast surfaces, in nuclei and in cytoplasmic strands between plastids. Myosin labeling also occurs in association with pyrenoids primarily in apical chloroplasts. During wound-induced cytoplasmic contractions, myosin is localized near the plasma membrane in longitudinal arrays superimposed over a reticulate pattern of fluorescence; both these patterns become apparent upon wounding. Double-label immunofluorescence of actin and myosin demonstrates that these arrays represent the longitudinal bundles of actin microfilaments and the actin-containing reticulum, the former being directly associated with contraction in these cells. These results indicate that both actin and myosin are associated with contractility in Ernodesmis, probably representing the apparatus and "molecular motor", respectively, which effect motility.