Dynamics of heat-induced thermal stress resistance and Hsp70 expression in the springtail, Orchesella cincta

1. The relationship between thermal resistance and expression of inducible heat shock proteins, especially Hsp70, depends on the species and temperature treatments. The induction of Hsp70 has been shown to be essential for heat stress survival in a number of species, yet the maximum protein expression levels do not coincide with peak survival after heat hardening in Drosophila. 2. Here we study the functional relationship between heat-induced expression of the heat shock protein Hsp70, and thermal resistance in adult Orchesella cincta by comparing thermal resistance (survival of 37-4 degrees C for 60 min) with Hsp70 gene and protein expression levels, all three measured at time points 2, 4, 6, 23, 27, 49 h after a heat hardening treatment (35-4 degrees C for 60 min). 3. Thermotolerance increased over time after heat hardening until 49 h after exposure when the experiment ended. On the other hand the expression of hsp70 messenger RNA reached a peak within the first 2 h and then sharply decreased after 6 h. Within 23 h hsp70 expression was back to control levels. 4. Surprisingly, protein levels of Hsp70 followed thermotolerance and reached the highest levels 49 h after heat hardening. A significant positive association was found between thermotolerance and Hsp70 protein levels, but not with hsp70 mRNA levels. 5. Our results support a strong correlation between Hsp70 expression levels and thermal resistance following a heat hardening treatment. They also show that gene and protein expression follow different dynamics, a difference that may be important for our understanding of the role of candidate genes in functional studies.