Temperature dependence and acclimatory response of amylase in the High Arctic springtail Onychiurus arcticus (Tullberg) compared with the temperate species Protaphorura armata (Tullberg)
Amylolytic activity was measured in whole body homogenates of High Arctic (Onychiurus arcticus) and temperate (Protaphorura armata) springtails (Collembola: Onychiuridae) in the temperature range 5–55°C. A pH of ca. 8 was optimum for amylolytic activity in both species. A higher weight-specific amylolytic activity was observed in P. armata. In O. arcticus, amylolytic activity depended on thermal acclimation, which increased during 2 and 9 weeks of cold acclimation (5°C) and decreased over 7 weeks of warming (15°C) of animals that were previously acclimated to cold for 2 weeks. In cold-acclimated O. arcticus, a slower decrease of amylolytic activity occurred with lowering of temperature in the range 5–20°C in comparison with warm-acclimated specimens and P. armata, which resulted in higher activity at 5°C. The activation energy calculated from an Arrhenius plot for P. armata was 68.7 kJ.mol−1. In O. arcticus it was between 30.2 and 61.5 kJ.mol−1, being lower in cold-acclimated samples. The temperature optimum for amylolytic activity was higher in the temperate species (40°C), whilst in O. arcticus it depended on the acclimation regime: it rose to 35°C after warm acclimation and decreased to 20°C after cold adaptation. The total soluble protein content of body tissues of O. arcticus also increased during cold acclimation. These differences between the two species suggest that amylolytic activity is an indicator of cold adaptation in the High Arctic O. arcticus.