Increases in tissue amino acid levels in response to ammonia stress in the terrestrial isopodPorcellio scaber Latr.

Abstract

Terrestrial isopods excrete waste nitrogen by intermittent volatilization of ammonia and must therefore accumulate amino groups in a non-toxic form between excretory bouts. High-performance liquid chromatography (HPLC) was used to analyze concentrations of 23 amino acids in the oniscidean Porcellio scaber following a 7-day exposure to elevated PNH3 (“ammonia stressing”). Analyses were performed on four separate tissues: hindgut, hepatopancreas, pleopodal endopods, and the body wall. Concentrations of all free amino acids except histidine and cysteine increased in ammonia-stressed animals. The greatest whole-animal concentrations (30–40 μmol·g fw−1) were seen in glutamine and glycine, which also showed the largest increases (fourfold). Most glutamine and glycine is accumulated in the body wall and hepatopancreas with concentrations in the hepatopancreas reaching 400–500 μmol·g fw−1. Ammonia-stressed animals showed smaller but substantial accumulations of alanine, arginine, proline, and glutamate. Arginine, by virtue of its 3N R-group, constitutes the major nitrogen-storage compound, together with glutamine. Calculations based on these and our previous data indicate that the amino acids constitute the primary form in which nitrogen is accumulated under ammonia-stressing conditions. © 1996 Wiley-Liss, Inc.