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 Cd 2+, which did not delay mitosis, elicited a protective response against a mitotic delay resulting from subsequent exposure to a suprathreshold challenge of Cd 2+. Some characteristics of this protective response are herein identified. The concentration of Cd 2+ in the subthreshold challenge could be lowered to 10 −5 m and maintain complete protection against a suprathreshold challenge of 5 × 10 −4 m Cd 2+. A subthreshold challenge of 10 −4 m provided full protection against a Cd 2+ concentration of 7 × 10 −4 m. A subthreshold challenge of 10 −4 m Cd 2+ could be placed anywhere in the cell cycle approaching but not abutting a suprathreshold challenge of 5 × 10 −4 m Cd 2+ in late G 2 and still provide complete protection with the exception of one point in early S. At that point, 10 −4 m Cd 2+ by itself was toxic to the cell; partial protection, however, developed. Other responses developed when metals were substituted for cadmium. Cd 2+ protected against exposure to Hg 2+ and Ni 2+ but potentiated exposures to Co 2+, Cu 2+, Pb 2+, or Zn 2+. A curious observ ation is that exposure to Hg 2+ and Ni 2+ protected against exposure to Cd 2+, while exposure to Co 2+, Pb 2+, or Zn 2+ potentiated exposure to Cd 2+. Hg 2+ and Ni 2+ protected against reexposure to themselves.