Heterogeneity and photoinhibition of photosystem II studied with thermoluminescence

Thermoluminescence (TL) signals were recorded from grana stacks, margins, and stroma lamellae from fractionated, dark-adapted thylakoid membranes of spinach (Spinacia oleracea L.) in the absence and in the presence of 2,6-dichlorphenylindophenol (DCMU). In the absence of DCMU, the TL signal from grana fractions consisted of a homogenous B-band, which originates from recombination of the semi-quinone QB- with the S2 state of the water-splitting complex and reflects active photosystem II (PSII). In the presence of DCMU, the B-band was replaced by the Q-band, which originates from an S2QA- recombination. Margin fractions mainly showed two TL-bands, the B- and C-bands, at approximately 50 degreesC in the absence of DCMU, and Q- and C-bands in the presence of DCMU. The C-band is ascribed to a TyrD+-QA- recombination. In the absence of DCMU, the fractions of stromal lamellae mainly gave rise to a TL emission at 42 degreesC. The intensity of this band was independent of the number of excitation flashes and was shifted to higher temperatures (52 degreesC) after the addition of DCMU. Based on these observations, this band was considered to be a C-band. After photoinhibitory light treatment of uncoupled thylakoid membranes, the TL intensities of the B- and Q-bands decreased, whereas the intensity at 45 degreesC (C-band) slightly increased. It is proposed that the 42 to 52 degreesC band that was observed in marginal and stromal lamellae and in photoinhibited thylakoid membranes reflects inactive PSII centers that are assumed to be equivalent to inactive PSII QB-nonreducing centers.