PIGMENTS AND PLASTIDS IN CULTURES OF TOTIPOTENT CARROT CELLS

Cells from a strain of carrot which was prone to form deep-seated chlorophyll in its storage organ have been cultured in a manner that promoted them to organize into plantlets. Whereas the free cells contained only chloroplasts, the plantlets derived from these cells formed all types of plastids (“proplastids,” leucoplasts, chromoplasts, and chloroplasts) in accordance with the location of the cells in question in the developing plant body. The developmental history of the plastids has been traced with the electron microscope. The events of chloroplast development, previously described by Israel and Steward (1967) for cultured carrot explants, have been verified. The bearing of this new evidence upon the control of plastid development and biochemistry is discussed and related to other recent studies. The conclusion is that all totipotent carrot cells have plastids as essential organelles but that their final form and content are sharply defined by the factors inherent in the location of the cells in the plant body as it emerges.