Activity of pyruvate kinase and malate dehydrogenase in Daphnia magna under 3,4-dichloroaniline stress

Abstract

Stressors can induce specific responses in enzyme function and energetic equilibrium. The hypothesis is tested that there are metabolic responses to stress, measured by a change in specific activity of piruvate kinase (PK) and malate dehydrogenase (MDH). Individual D. magna clones were exposed to 3,4-dichloroaniline for 7, 14, or 21 days. Other performed experiments persued the probable adaptation of the organisms borne under stress vs unstressed conditions. PK and MDH activity levels were inhibited after 7 days of 3,4-DCA exposure, whereas 14 and 21 day exposures induced enzyme activities. Enzymatic activities of individuals born under 3,4-DCA stress and reared in a DCA-free medium were compared with enzyme activities from individuals born and reared under control-M4 conditions. The inhibition of MDH at 7 and 21 days in these animals is similar to the responses of stressed animals in the initial phase of increased production. There was no significant effect on fecundity in DCA-tolerant animals. However, when the first generation of parents (under stress) were compared to DCA-tolerant animals (offsprings grown under normal culture conditions), a significant increase in fecundity was observed. This agrees with the decreased respiration under non-toxic conditions, hence, lower metabolic costs result during unstressed conditions, which may be an adaptative response to an environment free of stress.