Protoplasts were isolated from four strains of a primitive filamentous brown alga, Pilayella littoralis (L.) Kjellm. (Phaeophyceae) cultured in the same axenic conditions. Protoplast yields were different according to the strain and the concentrations of sodium citrate, a chelator of Ca2+ ions which are known to be involved in the cohesion of the alginate matrix. All protoplasts were able to regenerate and to produce new thalli. Regeneration times varied with the strain, but the modalities were the same. One of the strains, "Pil-Hel", is always fertile, bearing unilocular and plurilocular zoidangia. After enzymatic digestion of "Pil-Hel", protoplasts and zoids were recognizable and showed a different pattern of development. Protoplasts developed as did the zoids from unilocular sporangia. Differences observed between strains could be related to differences in the genotype, a hypothesis which seems supported by the existence of differences between the restriction patterns of chloroplastic DNA in two of these strains.
