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 [15], 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. The regulation
of structural proteins is further discussed in the following section.