Intracellular Composition and Net Release Rates of Free Amino Acids in Daphnia magna

Publisher Website
Google Scholar
Abstract
Excretion of free amino acids and ammonia by Daphnia magna was measured by examining in vitro changes in concentration of the two forms of nitrogen over 4–6 h. Mean weight-specific amino acid release rate (± SE) for 32 healthy daphnids was 0.13 ± 0.03 nmol (mg dry wt)−1∙h−1 as compared with a mean ammonia excretion rate of 21 ± 2 nmol (mg dry wt)−1∙h−1. Net removal from solution was observed when low levels of amino acids (2 nmol/8 mL) were added to the water before incubation, indicating that measured net release rates could be reduced by amino acid uptake. Toxic levels (0.5 mg∙L−1) of lead, arsenic, Kepone, toxaphene, malathion, or pentachlorophenol, added to stress the animals, did not significantly affect release rates of amino acids or ammonia, but the addition of copper (as CuSO4) increased amino acid release by daphnids and hindered microbial removal of amino acids from incubation waters. Amino acids released from copper-exposed animals were similar in composition to those in intracellular amino acid pools of D. magna, suggesting that diffusion across cell membranes may have been the mechanism for amino acid release.Key words: amino acids, ammonia, cladocera, contaminants, copper, Daphnia, excretion, free amino acids, stress, zooplankton

This publication has 2 references indexed in Scilit: