Figure 5.

Leaf metabolic amounts (A and B) and PPDK activity (C) in cocklebur, in the dark and in the light (400 μmol mol⁻¹ CO₂, 21% O₂, 23.5°C, 300 μmol mol⁻¹ PAR, no labeling). PEP content was determined by quantitative ³¹P-NMR from perchloric extracts. ATP-ADP and ATP-AMP ratios were measured on the same extracts with liquid-chromatography/time-of-flight mass spectrometry. In vitro PPDK activity (nmol PEP m⁻² s⁻¹) was measured on desalted leaf extracts using a PEPc-malate dehydrogenase coupled enzymatic assay. Values are mean ± se (n = 3).