Thermal Reaction between two Light Reactions in Photosynthesis

Energy Conservation in Photosynthetic Electron Transport of Chloroplasts

“…Artificial electron acceptors may be reduced by photosystem II to yield a Hill reaction (oxygen evolution and reduction of an acceptor) without the participation of photosystem I. Ferricyanide and DCIP were often considered in the past to be electron acceptors of photosystem II (16,188,190,197,220,249,257,312), but conflicting results emerged, particularly from measurement ofthe quantum require ment and enhancement because, contrary to the above authors, others did find enhancement (39,98,308). The problem of the specificity of photo reductions by photosystem II recently has been resolved.…”

Potentiometrically Measured Reduction of Low Concentrations of Dye by Illuminated Chloroplasts

“…In such a system a different dark reaction is rate limiting at normally used concentrations of oxidant (9,12). The photochemical evolution of oxygen is included in this age-inactivated part (9,18), but the data of Witt et al (18) indicate that the labile site is actually the temperature dependent component, E, catalyzing electron transport from the photochemical oxidation of OHto the photochemical reduction of TPN or added oxidants (see also 6,16). With the aging of chloroplasts the normal electron flux to cytochrome f is decreased, so the oxidized form of the cytochrome becomes increasingly available to react with reduced DPIP (18).…”

“…According to a wide convergence of evidence indophenol dyes are reduced more simply and rapidly than is ferricyanide, by illuminated chloroplasts (5,6,14,16,17,18). In fact it seems probable that the two oxidants are reduced by different sites of electron transport in the chloroplasts.…”

Electron Transport Pathways in Photosynthesis

“…Earlier workers had shown that the yield of oxygen from a long flash of light (25 to 35 msec) was more than doubled if a brief flash « 1 msec), which by itself yielded no oxygen, was presented about 30 to 700 msec ahead of the long fl ash (247 ). This was interpreted as an involvement of a photochemical activation step followed by a dark reaction which together yielded an active photochemical substrate for continuing oxygen evolution.…”