Hypoxia response in barley - proteomics analysis

Hypoxia stress (<1% oxygen) followed by reoxygenation, is accompanied by formation of reactive oxygen species (ROS) and nitric oxide (NO), which act as signaling molecules, but also cause nitro-oxidative stress. The NO concentration is regulated by phytoglobins (formerly hemoglobins) in the NO cycle. To understand how changes in phytoglobin expression affect plant metabolism under hypoxia, we studied the proteome and metabolome of barley (Hordeum vulgare L., cv. Golden Promise) plants without (WT) or with (HO) overexpression of phytoglobins. WT plants were more susceptible to hypoxia than HO. The chlorophyll a+b content was lowered by 50% and biomass by 30% in WT24, compared to WT, while HO plants were unaffected. We observe increase in ROS production during hypoxia treatment in WT seedlings had that was not observed in HO seedlings. But most importantly we identified and quantified 9694 proteins out of which 1107 changed significantly in abundance in at least one of the four comparisons – HO/WT andHO24/WT24) (giving genotype differences), WT24/WT and HO24/HO giving treatment differences. The main proteome changes between genotypes shown that many proteins were downregulated in HO24/HO but not in WT24/WT, such as ion transporters, Ca2+ signal transduction, and proteins related to protein degradation. We also identified and quantified 1470 metabolites, and the abundance of >500 changed significantly. Hypoxia had a much larger overall effect on the metabolome than overexpression of phytoglobin. The metabolites that have the biggest influence on the differences between treatments were selected for further analysis, among them many amino acids, putrescine and metabolites taking part in glycolysis.