Summary• Whereas mycorrhizal fungi are acknowledged to be the sources of nitrogen (N) and carbon (C) in achlorophyllous (myco-heterotrophic) orchids, the sources of these elements in autotrophic orchids are unknown. We have determined the stable isotope abundance of N and C to quantify their gain from different sources in these two functional groups and in non-orchids of distinctive mycorrhizal types.• Leaves of each plant were collected from four forest and four grassland sites in Europe. The N and C isotope abundance, and total N concentrations of their tissues and of associated soils were determined.• Myco-heterotrophic orchids were significantly more enriched in 15 N ( ε MHO-R = 11.5‰) and 13 C ( ε MHO-R = 8.4‰) than co-occurring non-orchids. δ 15 N and δ 13 C signatures of autotrophic orchids ranged from values typical of non-orchids to those more representative of myco-heterotrophic orchids.• Utilization of fungi-derived N and C probably explains the relative 15 N and 13 C enrichment in the myco-heterotrophs. A linear two-source isotopic mixing model was used to estimate N and C gain of autotrophic orchids from their fungal associates. Of the putatively autotrophic species, Cephalanthera damasonium obtained the most N and C by the fungal route, but several other species also fell into the partially myco-heterotrophic category.

The presented results facilitate the integration of pregnancy-dependent changes in anatomy and physiology into mechanistic population physiologically based pharmacokinetic models. Such models can ultimately provide a valuable tool to investigate the pharmacokinetics during pregnancy in silico and support informed decision making regarding optimal dosing regimens in this vulnerable special population.

The primary electron transfer in reaction centers ofRhodobacter sphaeroides is studied by subpicosecond absorption spectroscopy with polarized light in the spectral range of 920-1040 nm. Here the bacteriochlorophyll anion radical has an absorption band while the other pigments of the reaction center have vanishing ground-state absorption. The transient absorption data exhibit a pronounced 0.9-ps kinetic component which shows a strong dichroism. Evaluation of the data yields an angle between the transition moments of the special pair and the species related with the 0.9-ps kinetic component of 26 ± 8. This angle compares favorably with the value of 29°expected for the reduced accessory bacteriochlorophyll. Extensive transient absorbance data are fufly consistent with a stepwise electron ransfer via the accessory bacteriochlorophyll.In the primary processes of bacterial photosynthesis, absorbed light energy is stored via an electron transfer within the reaction center (RC). While the molecular structure of two bacterial reaction centers has been known for a number of years (1-3), the detailed molecular mechanism of the electron transfer is still the subject of intense investigations (4-20). There is general agreement that the first electron transfer process starts at a pair of bacteriochlorophyll (BChl) molecules-the special pair P-which acts as the primary donor. The

The modification of reaction centers from Rhodobacter sphaeroides by the introduction of pheophytins instead of bacteriopheophytins leads to interesting changes in the primary photosynthetic reaction: long-living populations of the excited electronic state of the special pair P* and the bacteriochlorophyll anion Bi show up. The data allow the determination of the energetics in the reaction center. The free energy of the first intermediate P+Br , where the electron has reached the accessory bacteriochlorophyll BA lies = 450 cm-' below the initially excited special pair P*.

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