Plants photosynthetic systems

In the light-driven primary charge separation processes of photosynthesis, the initial step involves irreversible electron transfer from the primary electron donor to an acceptor within 10 picoseconds [50]. In bacterial photosynthetic systems, it has been established that a BChl special pair acts as the primary electron donor, and that BChl and BPheo monomers act as acceptors [51]. Moreover, electron transfer in green plant photosynthetic systems is in generally known to involve Chi and Pheo moieties [41]. 

Photosynthesis is the reverse of reaction (30.1) the formation of carbohydrates and oxygen from water and carbon dioxide with solar energy. Photosynthesis occurs in the chloroplasts contained in the cells of green plants. The chloroplasts hold two types of photosynthetic systems, which are called PSl and PS 11. These systems... 

From a fundamental viewpoint, carbon dioxide reduction is a model reaction which can help us to understand better the mechanism of natural photosynthesis.11 Development of artificial photosynthetic systems, by mimicking functions of green plants, is one of... 

Photochemical fixation of carbon dioxide is a function of green plants and some bacteria in nature in the form of photosynthesis. All living organisms on the Earth are indebted directly or indirectly to photosynthesis. Thus, many attempts have been made to simulate the photosynthetic system and make artificial systems, although to date very little success has been achieved. 

Such a process can naturally be expected to play a certain part in the mechanism of directed energy transport in biological systems, in particular, in the transfer of absorbed energy from the antenna chlorophyll molecules to the reactive center in the photosynthetic system of plants. In Ref. [30], energy exchange between molecules of the photosynthetic pigments chlorophyll a and pheophytin a was studied experimentally with pigments introduced into the polar matrix. 

Although studied in great detail, the action of chlorophyll is still not fully understood however, steady progress towards a more complete understanding has taken place over the past several decades. Two photosynthetic systems (photosystems I and II) are present in green plants - each incorporating a different chlorophyll type. When a photon is absorbed by a chlorophyll molecule, its energy is transformed and... 

For the formation of one 02 molecule four electrons have to be transferred. This requires a "quantum storage device". In the photosynthetic system of green plants this is achieved with two photosystems that are linked through an electron transport chain, Fig. 10.2, and by means of the thylakoid-membrane that enables the separation of the photoproducts 02 and the reduced form of nicotinamide adenine dinucleotide phosphate, NADPH. 

The oxygen-evolving photosynthetic systems are exposed to the damaging effects of light, and without the repair machinery present in the plant, soon lose activity. Plants have mechanisms to minimize the damage, but these reduce the conversion efficiency. 

Cytochrome b(6)f protein complex, found in green plants, is part of the photosynthetic system—the principal producer of both oxygen and organic... 

It was hoped that structurally similar systems that would exhibit enhanced stability under experimental conditions could be produced in this fashion. (The Mn4 species present in the actual photosynthetic system has been difficult to study because of its instability when removed from the environment of the plant cell.)... 

Figure 5.4 Energy diagram of the two linked photosynthetic systems of green plants. The vertical scale is the energy (in eV) of an electron at the various stages of electron transport. P700 (pigment 700) and P680 (pigment 680) are chlorophylls with absorption maxima at 700 nm and 680 nm, respectively...

Photoelectrochemical conversion from visible light to electric and/or chemical energy using dye-sensitized semiconductor or metal electrodes is a promising system for the in vitro simulation of the plant photosynthetic conversion process, which is considered one of the fundamental subjects of modern and future photoelectrochemistry. Use of chlorophylls(Chls) and related compounds such as porphyrins in photoelectric and photoelectrochemical devices also has been of growing interest because of its close relevance to the photoacts of reaction center Chls in photosynthesis. 

Fujita, Y. and Murakami, A. 1987. Regulation of electron transport composition in cyano-bacterial photosynthetic system stoichiometry among PSI and PSII complexes and their light harvesting antenna and Cyt bt, f complex. Plant Cell Physiol. 28, 1547-1553. 

The oxidation of water to 02 in photosynthetic systems in plants has been greatly studied13 as have synthetic models such as those of manganese complexes the oxidation seems most likely to proceed via H202 rather than OH- radicals and probably two or four manganese centers are involved.14... 

Figure 2.14. Schematic picture of the components of the photosynthetic system in green plants and cyanobacteria, see text for explanation (Sorensen, 2004c with use of Protein Data Bank IDs IIZL (Kamiya and Shen, 2003), 1UM3 (Kurisu et al., 2003) and IJBO (Jordan et al, 2001)).

Fujita Y., Murakami A., and Ohki K. (1990) Regulation of the stoichiometry of thylakoid components in the photosynthetic system of cyanophytes model experiments showing that control of the synthesis or supply of Ch A can change the stoichiometric relationship between the two photosystems. Plant. Cell. Physiol. 31, 145-153. 

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