Cell repair through cell fusion in the red algaGriffithsia pacifica

Summary

When an intercalary shoot cell of the red algaGriffithsia pacifica is killed, the cell may be replaced through the wound-healing process of cell repair. During cell repair the cells on either side of the dead cell cut off new cells towards the dead cell. The superjacent cell produces a rhizoid; the subjacent cell produces an atypical shoot cell. The two new cells grow towards each other through the lumen of the dead cell. When they meet, they fuse; the resulting cell expands laterally to fill the cavity of the dead cell and is transformed into a typical intercalary shoot cell, morphologically and physiologically indistinguishable from the killed cell it replaces. The entire cell repair process takes 24–30 hours. Three aspects of cell repair suggest that intercellular communication occurs across the dead cell; these are a precocious division of the cell below the dead cell, a reversible change in the morphology and growth of the shoot cell which participates in repair, and a definite attraction between the two cells which fuse. Thus during cell repair we find evidence not only for cellular redifferentiation through cell fusion, but also for extracellular substances which change pathways of morphogenesis.