http://science.sciencemag.org/content/sci/168/3934/939.full.pdf

Chlorophyll, energy levels and electron flow in photosynthesis*

Cryobiology: The Freezing of Biological Systems

1
The relation between the “high energy state” of photophosphorylation and delayed fluorescence has been studied in spinach chloroplasts.

2
In the presence of an electron acceptor or cofactors, the kinetics of the rise in intensity of light emitted 1 millisecond after illumination showed two distinct phases,-a rapid phase complete in less than 0.1 s, and a sigmoidal slow phase with a halfrise time of about 0.3 s.

3
The maximal intensity and time course of emission were found to vary with electron flow and the degree of coupling. With nigericin or with NH4CI, the slow phase of the intensity rise was abolished but the rapid phase was unaffected. With valinomycin the rapid phase was substantially inhibited, but the extent of the slow phase was increased to give the same maximal intensity as observed in the absence of ionophore. With carbony cyanide p-trifluoromethoxy-phenylhydrazone (FCCP), or a combination of valinomycin and nigericin, both phases were substantially inhibited. This spectrum of sensitivities has been interpreted as showing that the slow phase depends on the pH component, and a part of the rapid phase on the electrical component, of the electro-chemical H+-gradient. Addition of 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea always inhibited emission.

4
A mechanism relating delayed fluorescence to the “high energy state” is suggested. The photochemical act of System II is envisaged as occurring between acceptor and donor sites on opposite sides of the thylakoid membrane and in equilibrium with pools the mid point potentials of which are dependent on the pH of the phase. It is shown that in such a system the energy conserved in the oxido reductive poise and in the electrochemical H+ gradient are additive and that both contribute to a decreased activation energy for delayed fluorescence. By dissipating the H+ gradient, the activation energy requirement is increased so that the intensity of emission falls.

5
It is concluded that other mechanisms for emission also operate, in particular one dependent on electron flow as such.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1971.tb01328.x

Delayed fluorescence and the high-energy state of chloroplasts.

The Evolution of Photosynthesis

One of the fundamental discoveries of W. Arnold was the detection of thermally stimulated light emission from preilluminated photosynthetic material (Arnold and Sherwood (1957) Proc Natl Acad Sci USA 43: 105–114). This phenomenon, called thermoluminescence (TL), is characteristic of a wide range of materials (semiconductors, minerals, inorganic and organic crystals, and complex biological systems such as the photosynthetic apparatus) which share the common ability of storing radiant energy in thermally stabilized trap states. The original discovery of TL in dried chloroplasts later proved to be a phenomenon common to all photosynthetic organisms: photosynthetic bacteria, cyanobacteria, algae and higher plants. Following the pioneering work of Arnold, considerable effort has been devoted to identification and characterization of photosynthetic TL components. This work has firmly established the participation of various redox states of the water-oxidizing complex and the quinone electron acceptors of Photosystem II in the generation of photosynthetic glow curves. Since TL characteristics are very sensitive to subtle changes in redox properties of the involved electron transport components, the TL method has become a powerful tool in probing a wide range of PS II redox reactions. In this paper, we will review the impact of Arnold's work in initiating and promoting TL studies in photosynthesis and will cover the most important developments of this field of research until the present day.

background or methods

Thermoluminescence from the photosynthetic apparatus

Chapter 1 – CHLOROPHYLL FLUORESCENCE AND PHOTOSYNTHESIS: FLUORESCENCE TRANSIENTS

https://www.pnas.org/content/pnas/61/1/29.full.pdf

Chlorophyll, energy levels and electron flow in photosynthesis*

Citations

Cryobiology: The Freezing of Biological Systems

Delayed fluorescence and the high-energy state of chloroplasts.

The Evolution of Photosynthesis

Thermoluminescence from the photosynthetic apparatus

Chapter 1 – CHLOROPHYLL FLUORESCENCE AND PHOTOSYNTHESIS: FLUORESCENCE TRANSIENTS

References

Ions in solution

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