ACTIVITY OF PYRUVATE-KINASE AND MALATE-DEHYDROGENASE IN DAPHNIA-MAGNAUNDER 3,4-DICHLOROANILINE STRESS

Stressors can induce specific responses in enzyme function and energet ic equilibrium. The hypothesis is tested that there are metabolic resp onses to stress, measured by a change in specific activity of piruvate kinase (PK) and malate dehydrogenase (MDH). Individual D. magna clone s were exposed to 3,4-dichloroaniline for 7, 14, or 21 days. Other per formed experiments persued the probable adaptation of the organisms bo rne 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 individu als born under 3,4-DCA stress and reared in a DCA-free medium were com pared with enzyme activities from individuals born and reared under co ntrol-M4 conditions. The inhibition of MDH at 7 and 21 days in these a nimals is similar to the responses of stressed animals in the initial phase of increased production. There was no significant effect on fecu ndity in DCA-tolerant animals. However, when the first generation of p arents (under stress) were compared to DCA-tolerant animals (offspring s grown under normal culture conditions), a significant increase in fe cundity was observed. This agrees with the decreased respiration under non-toxic conditions, hence, lower metabolic costs result during unst ressed conditions, which may be an adaptative response to an environme nt free of stress.