Compared thermoluminescence characteristics of pea thylakoids studied in vitro and in situ (in leaves). The effect of photoinhibitory treatments

Abstract

Characteristics of thermoluminescence (TL) glow curves were studied in thylakoids (isolated from pea leaves) or in intact pea leaves after an exposure to very high light for 2 min in the TL device. The inhibition of photosynthesis was detected as decreases of oxygen evolution rates and/or of variable fluorescence.In thylakoids exposed to high light, then dark adapted for 5 min, a flash regime induced TL glow curves which can be interpreted as corresponding to special B bands since: 1) they can be fitted by a single B band (leaving a residual band at -5°C) with a lower activation energy and a shift of the peak maximum by -5 to -6°C and, 2) the pattern of oscillation of their amplitudes was normal with a period of 4 and maxima on flashes 2 and 6. During a 1 h dark adaptation, no recovery of PS II activity occurred but the shift of the peak maximum was decreased to -1 to -2°C, while the activation energy of B bands increased. It is supposed that centers which remained active after the photoinhibitory treatment were subjected to reversible and probably conformational changes.Conversely, in intact leaves exposed to high light and kept only some minutes in the dark, TL bands induced by a flash regime were composite and could be deconvoluted into a special B band peaking near 30°C and a complex band with maximum at 2-5°C. In the case of charging bands by one flash, this low temperature band was largely decreased in size after a 10 min dark adaptation period; parallely, an increase of the B band type component appeared. Whatever was the flash number, bands at 2-5°C were suppressed by a short far red illumination given during the dark adaptation period and only remained a main band a 20°C; therefore, the origin of the low temperature band was tentatively ascribed to recombinations in centers blocked in state S2QA (-)QB (2-). In vivo, the recovery of a moderately reduced state in the PQ pool, after an illumination, would be slow and under the dependence of a poising mechanism, probably involving an electron transfer between cytosol and chloroplasts or the so-called 'chlororespiration' process.

Photoprotection of Photosystem II: Reaction Center Quenching Versus Antenna Quenching

“…This is consistent with the thesis that Q − A accumulates in PS II reaction centers of cold hardened pine needles to a greater extent than that in non-hardened pine needles due to an over-reduced PQ pool. These results are in agreement with earlier reports indicating that DCMU mimics the effects of low temperature photoinhibition of PS II in pine (Öquist and Martin, 1980), Pisum sativum (Farineau, 1993), and Chlamydomonas reinhardtii (Ohad et al, 1988). The lower total TL emission from winter pine needles and the relatively strong Z v band accounting for almost 60% of the total luminescence is indicative of a preferred back reaction of Q A with primary donors and a low probability of transfer of electrons from Q A to Q B ).…”

Effects of dark- and light-induced proton gradients in thylakoids on the Q and B thermoluminescence bands

“…Two major differences exist between the experiments reported here and the photoinhibitory experiments of Ohad et al (1988) and Farineau (1993), in which (i) continuous illumination represents a much higher amount of light energy than we used (ii) their TL recording was started at freezing temperatures while we always maintained the sample above 0 °C (iii) some time elapsed between illumination and TL recording. Although some of our experiments (not shown) indicate that the proton gradient can withstand a short freezing period in pea or spinach thylakoids or leaves, the downshift observed using the usual freezing TL conditions probably results mainly from a reduction of the PQ pool.…”

“…The appearance of a B-band at lower temperature has been reported after illumination at chilling temperatures in algae (Ohad et al 1988), in thylakoids and leaves (Farineau 1993). This can be explained as a reduction of the PQ pool, leading to a faster luminescence decay, an effect which can be suppressed by adding an electron acceptor such as methylviologen (Rutherford and Inoue 1984).…”

Seasonal responses of photosynthetic electron transport in Scots pine ( Pinus sylvestris L.) studied by thermoluminescence

“…5) and are presented as a percentage of the total TL light emission. Mean values ± SE were calculated from three to five independent experiments (Briantais et al 1992), and in pea thylakoids and leaves photoinhibited at chilling temperatures (Farineau 1993). The temperature shift of S 2 Q B -was interpreted in terms of production of inactive ''missing'' PSII reaction centers during cold acclimation and photoinhibitory treatment (Briantais et al 1992).…”