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First published online June 15, 2006
Journal of Experimental Biology 209, 2462-2471 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02268
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Mitochondrial mechanisms of cold adaptation in cod (Gadus morhua L.) populations from different climatic zones

M. Lucassen*, N. Koschnick, L. G. Eckerle and H.-O. Pörtner

Alfred-Wegener-Institute for Polar and Marine Research, Physiology of Marine Animals, Am Handelshafen 12, 27570 Bremerhaven, Germany


Figure 1
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  		Fig. 1. Effects of temperature acclimation on mRNA levels of (A) citrate synthase and (B) cytochrome c oxidase subunit 2 in white muscle of G. morhua from North Sea (NSC) and Barents Sea (NEAC). The relative quantities of CISY and COX2 were determined from ribonuclease protection assays. Data were corrected for loading differences using the 18S rRNA signal. Values are means ± s.e.m. (N=5–6) and expressed relative to the warm-acclimated control group (NSC, 10°C), which was set to 1. The data were tested for outliers at the 95% significance level using Nalimov's test (Noack, 1980Go). *Significant difference from the warm-acclimated control group within a population; *significant difference between populations at the same acclimation temperature.

 

Figure 2
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  		Fig. 2. mRNA levels of (A) citrate synthase and (B) cytochrome c oxidase subunit 2 in the liver of G. morhua from North Sea (NSC) and Barents Sea (NEAC), respectively, acclimated to 4°C and 10°C. The relative quantities of CISY and COX2 were determined from ribonuclease protection assays. Data were corrected for loading differences using the 18S rRNA signal. Values are means ± s.e.m. (N=5–6) and expressed relative to the warm-acclimated control group (NSC, 10°C), which was set to 1. The data were tested for outliers at the 95% significance level using Nalimov's test (Noack, 1980Go). *Significant difference from the warm-acclimated control group within a population; *significant difference between populations at the same acclimation temperature.

 

Figure 3
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  		Fig. 3. Effects of temperature acclimation on maximum activities of (A) citrate synthase and (B) cytochrome c oxidase in white muscle of G. morhua. Activities were measured at 10°C. Values are means ± s.e.m. (N=5–6). The data were tested for outliers at the 95% significance level using Nalimov'stest (Noack, 1980Go). *Significant difference from the warm-acclimated control group within a population; *significant difference between populations at the same acclimation temperature.

 

Figure 4
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  		Fig. 4. Maximum activities of (A,B) citrate synthase and (C,D) cytochrome c oxidase in liver of G. morhua after acclimation to 4°C and 10°C. Activities were measured at 10°C. The values in A and C are expressed relative to wet mass. For the calculation of activities in total liver (B,D) individual enzyme activities determined per g wet mass were multiplied by the hepatosomatic index thus yielding an activity value for all liver in 100 g fish. Values are means ± s.e.m. (N=5–6). The data were tested for outliers at the 95% significance level using Nalimov'stest (Noack, 1980Go). *Significant difference from the warm-acclimated control group within a population; *significant difference between populations at the same acclimation temperature.

 

Figure 5
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  		Fig. 5. Enzymatic activities versus mRNA levels in liver of cold acclimated G. morhua. (A) Citrate synthase (CS); (B) Cytochrome c oxidase (COX). Enzyme activities (per g fresh mass; 10°C assay temperature) and mRNA levels (per g fresh mass) were normalized by setting the mean activity of warm-acclimated G. morhua from the North Sea population to 1. Cold acclimation led to increments in maximum activities of both enzymes, reflecting a higher aerobic capacity in the Arctic population. Citrate synthase activities were significantly correlated with the increase in mRNA levels in both populations, in line with transcriptional control of this enzyme. No such correlation was found for cytochrome c oxidase activity and COX2 mRNA levels despite a significant increase in mRNA levels for the Arctic population. Open circles, G. morhua (North Sea, NSC); filled triangles, G. morhua (north eastern Arctic Sea NEAC). Broken line, line of identity for COX (y=1.0x).

 




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