The effects of temperature on specific dynamic action and protein synthesis rates in the Baltic isopod, Saduria entomon

The mean rate of oxygen consumption in fasted Saduria entomon increased between 4 degreesC and 13 degreesC with Q(10) of 2.33. After feeding, rates of oxygen uptake increased significantly by two- to threefold at both temperatures. However, the magnitude of the 'specific dynamic action of food' (SDA) response varied with temperature. At 4 degreesC, the magnitude was 45.5 +/- 4.2 mu mol, while at 13 degreesC, magnitude was significantly higher at 62.8 +/- 6.5 mu mol. In contrast, the duration of the response did not vary significantly with temperature in Saduria, with the consequence that the duration at 4 degreesC was considerably shorter than that measured at this temperature from an Antarctic isopod in a parallel study, and the duration at 13 degreesC was considerably longer than published values for temperate crustaceans at similar temperatures. Fasted rates of ammonia excretion increased with a Q(10) of 4.74 between 4 degreesC and 13 degreesC. The increase after feeding was sevenfold at 4 degreesC but only 2.6-fold at. 13 degreesC. Fasted O/N ratios for Saduria at 4 degreesC were about twice those at 13 degreesC. Fasted whole body protein synthesis rates (k(S)) increased with a Q(10) of 2.61 between 4 degreesC and 13 degreesC. Whole body k(S), measured at the peak of the SDA response, showed significant 2.7-and 1.9-fold increases at 4 degreesC and 13 degreesC, respectively, compared to fasted values, although the factorial rise at 130C was reduced compared to 4 degreesC. Alterations in k(S) rates after feeding at both temperatures resulted from significant increases in RNA activity (K-RNA) alone. However, the increase in k(S) between 4 degreesC and 13 degreesC was accompanied by increases in both K-RNA, and RNA/protein ratio, a measure of the capacity for protein synthesis (C-S). (C) 2001 Elsevier Science B.V. All rights reserved.