Photosynthesis, field effects

This volume of the series focuses on the photochemistry and photophysics of metal-containing polymers. Metals imbedded within macromolecular protein matrices form the basis for the photosynthesis of plants. Metal-polymer complexes form the basis for many revolutionary advances occurring now. The contributors to many of these advances are authors of chapters in this volume. Application areas covered in this volume include nonlinear optical materials, solar cells, light-emitting diodes, photovoltaic cells, field-effect transistors, chemosensing devices, and biosensing devices. At the heart of each of these applications are metal atoms that allow the assembly to function as required. The use of boron-containing polymers in various electronic applications was described in Volume 8 of this series. 

Several chapters of this book show how magnetic field effects, as well as CIDEP and CIDNP spectral patterns, can be used to solve chemical problems. It should be noted that the study of how applied magnetic fields perturb chemical reactivity is a topic that is highly relevant to biological processes involving radical pairs, for example, photosynthesis. ... 

Electric field effects play an important role in many biological cell processes. Phenomena as different as nerve excitation, electrogenic ion transport, neurostimulated secretion of hormones and transmitter substances, or the photosynthesis of involve cell functions in which... 

Until recently, the accumulated experimental information [2,3] provided strong support for the unistep superexchange mechanism. This evidence rested on direct information from fsec spectroscopy [2] and on supplementary information for electric field effects on fluorescence polarization [3]. Recent results [5,6] shed doubt on previous conclusions [2,3]. The direct fsec data of Holzapfel et al [5] demonstrate that the primary ET in Rb.sphaeraides at T = 300K can be analysed within the sequential mechanism (II) with = (3.5 psec) and = (0.9 psec) i, while the analysis of the electric field effects [3] is inconclusive [6]. At this exciting stage of the development of the field it is useful to turn to the theory regarding the elucidation of the primary process in photosynthesis. 

Haberkom, R., Michel-Beyerle, M.E. On the mechanism of magnetic field effects in bacterial photosynthesis. Biophys. J. 26, 489 98 (1979)... 

Plumley, EG. and D.E. Davis. 1980. The effect of a photosynthesis inhibitor atrazine, on salt marsh edaphic algae, in culture, microecosystems, and in the field. Estuaries 3 271-277. 

Such a photoinduced charge separation can proceed effectively provided an electric field (potential gradient) has been established at the position where the primary photoexcitation takes place. In general, a potential gradient can be produced at the interface between two different substances (or different phases). For example, a very thin (ca. 50 A) lipid membrane separating two aqueous solutions inside the chloroplasts of green plants is believed to play the essential role in the process of photosynthesis, which is the cheapest and perhaps the most successful solar conversion system available. 

As pointed out above, the bioassay design depends on the objective(s) of the study. A bioassay to determine allelopathic interactions in the field or in an ecological setting may have a quite different design than one used to determine PGR activity of a compound or to determine its molecular mode of action. Specific bioassays can be used to follow the isolation/purification of allelochemicals, evaluate their phytotoxic (or growth simulation) effects (i.e., visual effects), determine their host range/selectivity, evaluate allelopathic action of volatile compounds, or examine physiological/biochemical effects, such as photodynamic and membrane effects, effects on photosynthesis, specific enzyme sites, and effects at the ultrastructural level to locate receptor sites or sites of injury. Several examples of useful bioassays will be presented later. 

Plastoquinone is one of the most important components of the photosynthetic electron transport chain. It shuttles both electrons and protons across the photosynthetic membrane system of the thylakoid. In photosynthetic electron flow, plastoquinone is reduced at the acceptor side of photosystem II and reoxidized by the cytochrome bg/f-complex. Herbicides that interfere with photosynthesis have been shown to specifically and effectively block plastoquinone reduction. However, the mechanisms of action of these herbicides, i. e., how inhibition of plastoquinone reduction is brought about, has not been established. Recent developments haVe brought a substantial increase to our knowledge in this field and one objective of this article will be to summarize the recent progress. 

Microcosm and in situ field experimental studies of nutrient Hmitation of tropical algae have had conflicting results, adding fuel to this controversy. Across many systems and scales, effects of nutrient additions have varied from no effects (Delgado et al., 1996 Koop et al., 2001 Larkum and Koop, 1997) to orders of magnitude differences in effects on photosynthesis, growth, and biomass accumulation... 

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