A cellular model for studying accommodation to environmental stressors: protection and potentiation by cadmium and other metals.

Exposure of P. pdyrphczlum to a subthreshold challenge of Cd’+, which did not delay mitosis. elicited a protective response against a mitotic delay resulting from subsequent exposure to a suprathreshold challenge of Cd2+. Some characteristics of this protective response are herein identified. The concentration of Cd2+ in the subthreshold challenge could be lowered to lo-” M and maintain complete protection against a suprathreshold challenge of 5 X IO-’ M Cd?+. A subthreshold challenge of lOed M provided full protection against a Cd?concentration of 7 x IOM. A subthreshold challenge of lo-” M Cd’+ could be placed anywhere in the cell cycle approaching but not abutting a suprathreshold challenge of 5 X 10eJ M Cd’+ in late G, and still provide complete protection with the exception of one point in early S. At that point, 10.’ M Cdrf by itself was toxic to the cell: partial protection. however, developed. Other responses developed when metals were substituted for cadmium. C@+ protected against exposure to HgY+ and NiY+ but potentiated exposures to Co’+, Cu”, PW’, or Zn’+. A curious observation is that exposure to Hg’+ and NiY+ protected against exposure to Cd+, while exposure to Co”, PbY+, or Zn’+ potentiated exposure to Cd’+. HgL+ and Ni’+ protected against reexposure to themselves.