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.

The pyridine nucleotide levels and reduction charges in selected species of the plant kingdom are described. Data, determined in plants growing under natural conditions (without any treatment) are discussed from physiological and evolutionary aspects. The conclusions are based on the interpretation of data from representative plants of 40 species, using own results of 17 species and data from literature.

The pyridine nucleotide pattern and the reduction charges in wheat seedlings are described with regard to different photosynthetic conditions. The charges were examined during ontogenesis, after interruption of photosynthesis and under kinetin or DCMU treatment. The induced changes in catabolism or anabolism led to a specific pattern of pyridine nucleotides. The anabolic reduction charge remained relative constant after a long-term interruption of photosynthesis in the range of 0.70 in comparison with the control, but it changed during a short-term interruption. Independent of the duration of interruption the catabolic reduction charge value remained also constant in the range of 0.07–0.09 (7-day-old seedlings). DCMU and kinetin treatment did not change the redox state between the pyridine nucleotides. Interconversions between the pyridine nucleotide pools and the hexose monophosphate shunt are discussed as compensating mechanisms in order to maintain the redox level.

Intensity-dependent transmission measurements were carried out in vitro with chlorophyll solutions and in vivo with leaf segments of primary leaves of Triticum aestivum L. The results are discussed in relation to the size of the primary absorption unit (∼ 106 chlorophyll molecules) and the relative homogeneity of the red absorption band of chlorophyll in vivo.

The intensity-dependent transmission of primary leaves of Triticum aestivum seedlings at lambda = 694 nm was measured with single pulses of a Q-switch ruby laser. At photon flux densities above 2 x 10(17) cm-2s-1 a decrease of transmission was observed. The result is interpreted as a two-step absorption of cooperative units of 10(5)-10(6) chlorophyll molecules.

The changes of characteristic key enzymes of the nitrogen and carbon metabolism were studied during the greening process of isolated leaves of Triticum aestivum.

Stimulated emission of chlorophyll-a is observed in the spectral range around 670 nm. The calculated wavelength at the threshold turns out to be shifted by 20 nm towards longer wavelengths. To clarify this discrepancy, extrinsic-loss variations at the laser as well as measurements of nonlinear are carried out. The results indicate an excited singlet state absorption (σ > 10 17 cm 2 within the range from 670 to 700 nm).