Third-stage larvae of Pseudoterranova decipiens commonly infect whitefish such as cod, and the parasite can be transferred to humans through lightly prepared (sushi) meals. Because little is known about the nematode's cold tolerance capacity, we examined the nematode's ability to supercool, and whether or not cold acclimation could induce physiological changes that might increase its ability to tolerate freezing conditions. Even if third-stage Pseudoterranova decipiens larvae have some supercooling ability, they show no potential for freezing avoidance because they are not able to withstand inoculative freezing. Still, they have the ability to survive freezing at high subzero temperatures, something which suggests that these nematodes have a moderate freeze tolerance. We also show that acclimation to high temperatures triggers trehalose accumulation to an even greater extent than cold acclimation. Trehalose is a potential cryoprotectant which has been shown to play a vital role in the freeze tolerance of nematodes. We suggest that the trehalose accumulation observed for the cold acclimation is a general response to thermal stress, and that the nematode's moderate freeze tolerance may be acquired through adaptation to heat rather than coldness.

Wheat and barley seeds were subjected to accelerated aging conditions at 12% moisture content and 35°C temperature over 28 days of storage, and to heat-shock treatment carried out by 4 h of incubation at 40°C following 16 h of imbibition at 20°C. Heat-treated, aged seeds showed altered germination behaviour and increasing leakage electroconductivity as well as a reduced incorporation of [35S]-methionine into embryo proteins, in comparison with the corresponding untreated seeds. Two-dimensional electrophoresis of labelled proteins from embryos gave evidence of further quantitative and qualitative changes: (a) ‘normal’ germination protein synthesis in wheat and barley was slightly modified by age, but following heat-shock treatment a general reduction of most of the control polypeptides occurred; (b) heat-shock response resulted in the production of several HSPs with different MW and pl, but a uniform general decline in their synthesis was not observed. Highly labelled HSPs (e.g., those with MW 66.7 or 89.3–66.7 kDa in wheat or barley, respectively) did not change over the entire period of aging, while some smaller HSPs with MW >29 kDa either decreased in intensity or disappeared. Conversely, specific low molecular weight HSPs (MW 17–14.2 kDa) were synthesized more in extremely aged embryos of both species. The hypothesis that these polypeptides may be used as biochemical markers in monitoring both vigour loss and heat-shock induced tolerance in aged seeds is discussed.