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

Abstract

Exposure of P. polycephalum to a subthreshold challenge of Cd2+, 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 10-5 m and maintain complete protection against a suprathreshold challenge of 5 x 10-4 m Cd2+. A subthreshold challenge of 10-4 m provided full protection against a Cd2+ concentration of 7 x 10-4 m. A subthreshold challenge of 10-4 m Cd2+ could be placed anywhere in the cell cycle approaching but not abutting a suprathreshold challenge of 5 x 10-4 m Cd2+ in late G2 and still provide complete protection with the exception of one point in early S. At that point, 10-4 m Cd2+ by itself was toxic to the cell; partial protection, however, developed. Other responses developed when metals were substituted for cadmium. Cd2+ protected against exposure to Hg2+ and Ni2+ but potentiated exposures to Co2+, Cu2+, Pb2+, or Zn2+. A curious observ ation is that exposure to Hg2+ and Ni2+ protected against exposure to Cd2+, while exposure to Co2+, Pb2+, or Zn2+ potentiated exposure to Cd2+. Hg2+ and Ni2+ protected against reexposure to themselves.