Redox Status of Pyridine Nucleotides and O2 Gas Exchange of Picea abies (L.) Karst. Seedlings under Experimentally Induced Oxidative Stress

The amount and the redox status of pyridine nucleotides as well as OZ gas exchange and delayed fluorescence in spruce seedlings were examined after prolonged exposure to methyl viologen (25–200 ppm). During a period of 24 h, methyl viologen induced a significant decrease of NADPH + H⁺ compared with the control, resulting in a marked decrease of ARC (anabolic reduction charge: [NADPH + H⁺]/[NADPH + H+ + NADP⁺]). Later on, the ARC of treated samples remained on a constant level at least until 72 h, though the total content of phosphorylated pyridine nucleotides decreased. The CRC (catabolic reduction charge: [NADH + H⁺]/[NADH + H⁺ + NAD⁺]) of treated seedlings was lowered only transiently. This indicates that reducing equivalents contribute to the detoxification of reactive oxygen species only initially during methyl viologen application. The decrease of functions — photosynthesis, respiration — supports the view that after prolonged treatment the progressive damage of cell components rather than the availability of reducing equivalents limits the capacity of the plant tissue to detoxify methyl viologen-induced reactive oxygen species.