Different Modes of Cell Sterilization: Cell Killing and Early Differentiation

Abstract

Investigations in plants and parallel observations in animals suggest that specific interference with endocellular control of differentiation due to cytoplasmic growth during mitotic delay is involved in the sterilizing effect of radiation. A comparison was made of the effect of x and uv radiation on 3-day-old prothalli of Osmunda regalis (the royal fern). After increasing x-ray doses, an increasing proportion of cells reach terminal differentiation early, i.e., enlarge, form central vacuoles, and cease mitotic activity after fewer mitotic cycles than normal. This is defined as early differentiation. After 4 krad of x radiation most cells have reached terminal differentiation before the end of mitotic delay, and remain alive although they are sterile since mitotic activity is permanently inhibited. By contrast, uv radiation does not induce early differentiation, although mitotic delay is four times as long as after comparable sterilizing doses of x rays. Protein synthesis is normal or increased after x irradiation but is depressed after uv irradiation. Cells enlarge after x irradiation but not after uv irradiation. It is concluded that normal cytoplasmic growth continues after x irradiation and early differentiation is induced, but uv damage, presumably to mitochondria and proplastids, precludes this possibility. Ultraviolet radiation thus sterilizes bymore » prompt cell killing, whereas an efficient means of sterilization by x rays, even in certain tumors, is by the induction of early differentiation.« less