title: The Calvin cycle inevitably produces sugar-derived reactive carbonyl methylglyoxal during photosynthesis: a potential cause of plant diabetes.
abstract: Sugar-derived reactive carbonyls (RCs), including methylglyoxal (MG), are aggressive by-products of oxidative stress known to impair the functions of multiple proteins. These advanced glycation end-products accumulate in patients with diabetes mellitus and cause major complications, including arteriosclerosis and cardiac insufficiency. In the glycolytic pathway, the equilibration reactions between dihydroxyacetone phosphate and glyceraldehyde 3-phosphate (GAP) have recently been shown to generate MG as a by-product. Because plants produce vast amounts of sugars and support the same reaction in the Calvin cycle, we hypothesized that MG also accumulates in chloroplasts. Incubating isolated chloroplasts with excess 3-phosphoglycerate (3-PGA) as the GAP precursor drove the equilibration reaction toward MG production. The rate of oxygen (O2) evolution was used as an index of 3-PGA-mediated photosynthesis. The 3-PGA- and time-dependent accumulation of MG in chloroplasts was confirmed by HPLC. In addition, MG production increased with an increase in light intensity. We also observed a positive linear relationship between the rates of MG production and O2 evolution (R = 0.88; P < 0.0001). These data provide evidence that MG is produced by the Calvin cycle and that sugar-derived RC production is inevitable during photosynthesis. Furthermore, we found that MG production is enhanced under high-CO2 conditions in illuminated wheat leaves.
authors.affiliation: Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai, Nada, Kobe, 657-8501 Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Takagi
authors.forename: Hironori
authors.initials: H
authors.lastname: Inoue
authors.forename: Mizue
authors.initials: M
authors.lastname: Odawara
authors.forename: Ginga
authors.initials: G
authors.lastname: Shimakawa
authors.forename: Chikahiro
authors.initials: C
authors.lastname: Miyake
mesh_terms: D050260:Carbohydrate Metabolism; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism; D004099:Dihydroxyacetone Phosphate / Q000378:metabolism; D017127:Glycation End Products, Advanced / Q000378:metabolism; D005986:Glyceraldehyde 3-Phosphate / Q000378:metabolism; D008027:Light; D010100:Oxygen / Q000378:metabolism*; D010788:Photosynthesis; D018515:Plant Leaves / Q000502:physiology / Q000528:radiation effects; D010940:Plant Proteins / Q000378:metabolism; D018526:Plant Transpiration; D011765:Pyruvaldehyde / Q000378:metabolism*; D014305:Triose-Phosphate Isomerase / Q000378:metabolism; D014908:Triticum / Q000502:physiology* / Q000528:radiation effects
chemical_list: D017127:Glycation End Products, Advanced; D010940:Plant Proteins; D005986:Glyceraldehyde 3-Phosphate; D002245:Carbon Dioxide; D004099:Dihydroxyacetone Phosphate; D011765:Pyruvaldehyde; D014305:Triose-Phosphate Isomerase; D010100:Oxygen
keywords: Advanced glycation end-products; Methylglyoxal; Photosynthesis; Triose phosphate isomerase