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

Cryobiology: The Freezing of Biological Systems

Energy conversion in the functional membrane of photosynthesis. Analysis by light pulse and electric pulse methods: The central role of the electric field

DR. C. E. K. MEES, with the help of the Kodak Research Laboratories, has written a book that will be for many years the standard authority on the photographic process. His title describes the book as an account of the theory; but theory is not conceived in a narrow sense as the counterpart of experiment, but rather as including almost everything about photography except its practice. The first chapters deal with the emulsions, what they are made of and how they are prepared; the action of light is then described, the processes that take place in photographic materials under its influence and the large number of theories which has been advanced to account for them. Development and fixation are then discussed, again with the emphasis on the details of changes that take place in emulsions and on attempts to explain them in terms of physics and chemistry. There are further chapters on sensitometry, on the nature of the developed image and on the photographic aspects of sound recording. Finally an, account is given of the use of dyestuffs for the production of colour-sensitive film, and for desensitization. The Theory of the Photographic Process By Dr. C. E. Kenneth Mees. Pp. xi + 1124. (New York: The Macmillan Company, 1942.) 60s. net.

The Theory of the Photographic Process

Membrane surface charges and potentials in relation to photosynthesis

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.

— Green plants, after illumination, emit light at times far too long to be fluorescence. This delayed light is closely connected with the process of photosynthesis and seems to be one of the few ways of studying the first steps in that process. In this paper we argue that there are at least 3 or maybe 4 mechanisms producing delayed light. (1) The delayed light in the range of 1–100 msec seems to come from the recombination of electrons and holes. The photosynthetic unit must absorb 2 quanta for this process. (2) At longer times the delayed light can come from thermal fluctuations lifting an electron from the level of ferredoxin to that of chlorophyll. The unit need only absorb 1 light quantum for this kind of delayed light. (3) Similarly, a part of the long-time delayed light comes from the untrapping of holes. (4) A part of the delayed light emitted at times longer than a few minutes seems to involve molecular oxygen. Finally, we shall describe a new phenomenon involving the effect of electric fields on chloroplasts, that we feel will be helpful in understanding the untrapping mechanisms of delayed light production.

The mechanism of delayed light production by photosynthetic organisms and a new effect of electric fields on chloroplasts

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

Chlorophyll, energy levels and electron flow in photosynthesis*

An electrical field across a suspension of Chenopodium chloroplasts stimulates the emission of delayed light during the time the field is on. This stimulation can be used to calculate the distance over which the electron moves in the untrapping process that gives the delayed light. An electrical field applied at the time of illumination gives a polarization to the suspension of chloroplasts that lasts for some seconds. This polarization is a new way to study delayed light and fluorescence from chloroplasts.

Two effects of electrical fields on chloroplasts.

During green plant photosynthesis not all of the energy of the light absorbed by chlorophyll is used. A part, 2–3%, is re-emitted as fluorescence. A somewhat smaller part that we call delayed light is emitted at times of 10−5 sec to 3 hr after illumination, far too long to be fluorescence (1). This delayed light is closely connected with the process of photosynthesis and seems to be one of the few ways of studying the first steps in that process (2). While making such studies with “broken” chloroplasts, we observed that the delayed light could be stimulated by an electric field across the chloroplast suspension. This new effect is surprisingly large. A field of a few hundred volts/cm can increase the light emission by 50 times. We made a preliminary announcement of this phenomenon at the International Conference on the Photosynthetic Unit, held in Gatlinburg a year ago (3).

Electric Field and Chloroplast Membranes

The photochemistry done by single chloroplasts can be measured when the chloroplasts are embedded in nuclear track emulsion. It has been known for more than 50 years that certain chemicals will blacken photographic plates (chemical fogging). Although this effect has been little used to measure chemical reactions, it may be particulary useful in photochemistry and electrochemistry, since as little as 10(-18) mole can be measured.

http://science.sciencemag.org/content/sci/185/4145/59.full.pdf

Jim Azzi

Papers

The mechanism of delayed light production by photosynthetic organisms and a new effect of electric fields on chloroplasts

Chlorophyll, energy levels and electron flow in photosynthesis*

Two effects of electrical fields on chloroplasts.

Electric Field and Chloroplast Membranes

Photochemical Activity of Single Chloroplasts Recorded by the Use of Nuclear Track Emulsion