Main Objectives: Glycation is a non-enzymatic post-translational modification formed by reaction of reducing sugars (aldoses and ketoses) with amino groups of proteins, and resulting so-called Amadori and Heyns compounds, respectively. Their further oxidation and formation of α-dicarbonyls (glycoxidation) yield advanced glycation end-products (AGEs) known for their pro-inflammatory effects in humans. Though AGEs readily form during thermal processing of foods, it may occur also during the life time of crop plants. In this context, it is important to know the patterns of AGEs in crop plants and effect of environmental stress on their dynamics.

Strategy and Methods: The models of high light, drought and metal stress were established with Arabidopsis thaliana and Brassica napus. The leaves were harvested before stress application and in multiple points throughout the stress period. The analytical strategy (applied to A. thaliana and B. napus) relied on the combination of LC-based bottom-up proteomics (LC x LC-ESI-Orbitrap-LIT-MS/MS data dependent acquisition experiments), untargeted and targeted metabolomics (GC-EI-Q-MS) and model glycation experiments with synthetic peptides (LC-QqTOF-MS and MS/MS).

Main Results: Even unstressed plants displayed rich patterns of glycated and glycoxidated proteins (up to 400 and 900 modified peptides, respectively) mostly involved in regulatory pathways, protein and nucleic acid metabolism. The product structures were comprehensively characterized with ESI-MS/MS. Light and metal stress resulted in increased Amadori/Heyns product (mostly triose- and pentose-derived) formation. The number of AGE-modified sites (dominating with arginine residues) was essentially increased under drought and high metal concentrations (44 and 65 unique sequences, respectively), while all stresses resulted in significantly higher abundances of corresponding products. However, the majority of AGE-modified sites did not resemble glycated ones. Remarkably, all stresses caused significant up-regulation of tissue carbohydrates. As it was not accompanied with the elevation of free α-dicarbonyl levels, autoxidation of the carbohydrates followed by immediate binding of generated intermediates to cellular proteins and metabolites might be the most probable scenario. Reactivities, glycation and AGE-formation potentials of individual sugars were characterized by in vitro experiments with synthetic peptides. Thereby, D-glucoso-6-phosphate showed the highest reactivity, while dihydroxyacetone phosphate, D-glyceraldehyde and D-ribose demonstrated the highest potential for AGE formation.

Conclusions: The character and the scale of the changes in the protein glycation and glycoxidation patterns depended on the nature of environmental stress. Thus, oxidative glycosylation of proteins, rather than their glycoxidation or lipid peroxidation, was the main source of AGEs. Dihydroxyacetone phosphate, D-glyceraldehyde and D-ribose demonstrated the highest potential for AGE formation.