Thermoluminescence and P700 redox kinetics as complementary tools to investigate the cyclic/chlororespiratory electron pathways in stress conditions in barley leaves

Abstract

Cyclic electron flow around photosystem I drives additional proton pumping into the thylakoid lumen, which enhances the protective non-photochemical quenching and increases ATP synthesis. It involves several pathways activated independently. In whole barley leaves, P700 oxidation under far-red illumination and subsequent P700(+) dark reduction kinetics provide a major probe of the activation of cyclic pathways. Two 'intermediate' and 'slow' exponential reduction phases are always observed and they become faster after high light illumination, but dark inactivation of the Benson-Calvin cycle causes the emergence of both a transient in the P700 oxidation and a 'fast' phase in the P700(+) reduction. We investigate here the afterglow (AG) thermoluminescence emission as another tool to detect the activation of cyclic electron pathways from stroma reductants to the acceptor side of photosystem II. This transfer is activated by warming, yielding an AG band at about 45°C. However, treatments that accelerate the 'intermediate' and 'slow' P700(+) reduction phases (brief anoxia, hexose infiltration, fast dehydration of excised leaves) also produced a downshift of this AG band. This pathway ascribable to NADPH dehydrogenase (NDH) would be triggered by a deficit in ATP, while the 'fast' reduction phase corresponding to the ferredoxin plastoquinone reductase pathway is triggered by an overreduction of the photosystem I acceptor pool and is undetected in thermoluminescence. Contrastingly, slow dehydration of unwatered plants did not cause faster reduction of P700(+) nor temperature downshift of the AG band, that is no induction of the NDH pathway, whereas an increased intensity of the AG band indicated a strong NADPH + ATP assimilatory potential.

Lumen Thiol Oxidoreductase1, a Disulfide Bond-Forming Catalyst, Is Required for the Assembly of Photosystem II inArabidopsis

“…This would allow the mutants to use PSI and cytochrome b 6 f to pump protons and thereby synthesize ATP in the absence of significant levels of linear electron flow due to the deficiency in PSII. This would explain both the elevated F 0 level and the fact that P 700 + is rereduced much faster in the lto1 mutants compared with the wild type (see Supplemental Figure 2 online), an expected finding if cyclic electron transfer is elevated (Finazzi and Forti, 2004;Iwai et al, 2010;Peeva et al, 2010).…”

Photosynthetic proton and electron transport in wheat leaves under prolonged moderate drought stress

“…Therefore, the probability that an electron generated on the PSI acceptor side will be transferred to the linear pathway during the dark to light transition is proportional to the rate of P700 oxidation. In turn, the area above the P700 kinetic can be used for the relative amount of electrons (number of turnovers) recycled toward the intersystem chain and P700 + under FR light [52], hence, the increase of the area above the P700 kinetic curve is proportional to the fraction of P700 engaged in CET. For this purpose, we have analyzed the P700 kinetics of far-red pulses applied originally for ChlF F 0 0 determination.…”

Thioredoxin m4 Controls Photosynthetic Alternative Electron Pathways in Arabidopsis

“…In Arabidopsis, NDH-mediated electron transport in the dark can also be probed by measuring the afterglow (AG) luminescence signal Lintala et al, 2009;Peeva et al, 2012). Following FR illumination at 0°C, an AG thermoluminescence signal peaking at approximately 40°C was detected in control leaves in addition to the B band appearing at approximately 18°C to 20°C (Fig.…”

“…This band shift indicates a stimulated electron transfer rate from stroma to the PQ pool: electrons are rapidly transferred to the secondary quinone acceptor at room temperature, leading to charge recombinations within PSII and to an AG thermoluminescence band merged with the B band Apostol et al, 2006;Peeva et al, 2012). In previous works Peeva et al, 2012), the downward shift of the peak temperature of the AG band was correlated with an acceleration of CEF, as measured by the rate of rereduction of the oxidized primary electron donor in PSI (P 700 + ) in the dark following a FR light illumination. Leaf absorbance measurements at 820 nm, which reflects changes in the redox state of P 700 , were performed on Arabidopsis leaves (Fig.…”