Using in vitro peptide-based glycation models, reactivity and glycation potential of individual plant sugars were addressed and considered in the context of in vivo abundances of corresponding metabolites. Thus, approximately 800 individual AGE-modified proteins were annotated. The rates of glycation were increased under stress conditions and during the life span of experimental plants. Thereby, monosaccharide autoxidation was the major pathway of their formation, whereas dihydroxyacetone phosphate, glyceraldehyde-3-phosphate, ribulose, erythrose, and sucrose were the most probable plant AGE precursors. Analysis of α-dicarbonyl formation in model peptide-based glycation reactions performed with these sugars confirmed monosaccharide autoxidation as the principle glycation pathway in plants.