Thermoluminescence studies on the facultative crassulacean-acid-metabolism plant Mesembryanthemum crystallinum L.

Krieger A, Bolte S, Dietz K-J, Ducruet JM. Thermoluminescence studies on the facultative crassulacean-acid-metabolism plant Mesembryanthemum crystallinum L. Planta. 1998;205(4):587-594.Thermoluminescence (TL) signals were measured from leaves of the facultative CAM (crassulacean acid metabolism) plant Mesembryanthermum crystallinum L.. Following the induction of CAM by salt treatment, a TL band at 46 degrees C was induced, which was charged by a single-turnover flash. The intensity of the 46 degrees C-band depends on the number of excitation flashes and oscillates with a period of four. A similar band was induced in Cg plants by far-red illumination. Under CAM conditions, the intensity of the 46 degrees C-band underlies a diurnal rhythm. The maximal intensity of the 46 degrees C-band is observed in the morning after onset of the light and in the evening. At around 12 a.m. it is suppressed. The intensity of the 46 degrees C-band relates to diurnal changes in the ratio of dihydroxy acetone phosphate/3-phosphoglycerate (DHAP/PGA) which is an indicator of the energy status of the chloroplast. During high-intensity illumination, the 46 degrees C-band disappears, but it is restored in the dark. We propose that the 46 degrees C-band is an indicator of the metabolic state of the leaf, originating from photosystem II centres initially in the S-2(S-3)Q(B) oxidation state, in which the electron acceptor QB becomes reduced either by reverse electron flow or reduction of the plastoquinone pool via an NAD(P)H plastoquinone oxidoreductase. We present evidence that the redox state of the electron-transport chain is different under conditions of CAM compared to C-3 metabolism and that changes induced by CAM can be monitored by measuring the amplitude of the 46 degrees C-band after flash excitation