Pejus range protein network regulation
Stress level specific responses fall into two broad categories; upregulation in energy metabolism and variable regulation of structural proteins. Pejus range regulation networks include one with mostly upregulated proteins, many of which participate in amino acid metabolism. Downregulation of the proteasome affects both energy and amino acid metabolism. It reduces protein turnover to redirect energy towards osmoregulation and it may reduce the availability of free amino acids liberated from degraded proteins. As noted earlier, specific markers for passing the critical threshold into the pessimum range during thermal stress may not apply during salinity stress. Thermal stress is predicted to lead to increased lactate through anaerobic metabolism only above the critical threshold (Sokolova et al., 2012), whereas our data show upregulation in LDH only occurs in the 75g/kg treatment. Energy demand required in hypersalinity appears to be supplied mainly through oxidative phosphorylation and carbohydrate metabolism with some additional fatty acid β-oxidation. In addition, in the Pejus range, amino acid metabolism is significantly affected, which may contribute to the regulation of energy metabolism (e.g. via regulation of gluconeogenesis).
The other major protein network includes structural proteins such as several myosin subunits which are significantly upregulated in pejus range salinities but significantly downregulated in pessimum range salinities. However, tropomyosin β is significantly downregulated in the pejus range and upregulated (n.s.) in the pessimum range, and is one of the proteins most highly correlated with blood osmolality. The regulation of structural proteins is further discussed in the following section.