Fig. 5.

Chromatograms of o-phenylenediamine (OPD) derivatives of sugar-derived reactive carbonyls (RCs). Black line, 40 Pa CO₂; Red line, 90 Pa CO₂. Typical chromatograms of sugar-derived RCs are shown. AU indicates the relative absorbance units based on leaf area at 312 nm. Arrows indicate sugar-derived RCs, the levels of which increased at 90 Pa CO₂ (compared with 40 Pa CO₂). Glyoxal (GLO) and methyglyoxal (MG) were identified from the retention times of the commercially purchased compounds. Insets show typical MG and GLO peaks, which were normalized with the baseline. HPLC of sugar-derived RCs is described in the Materials and Method. R.T., retention time.