No abstract

Abstract— The origin of glow peaks (thermoluminescence) was investigated in isolated spinach chloroplasts and Euglena cells by pretreatment with various concentrations of 3‐(3,4 dichlorophenyl)‐1,1‐dimethylurea (DCMU)†, different light intensities, and after mild heating at various temperatures. Experiments are also reported on subchloroplast fractions enriched in pigment systems I (PSI) or II (PSII) (prepared under conditions to reduce destruction of membranes by excessive detergent contact). These results provide the following, most likely, suggestion for the origin of glow peaks: (1) Z peak originates in metastable states; it is insensitive to DCMU, temperature (320–328 K), and appears only when other peaks are saturated (10 Wm‐2). (2) Peak I involves the use of a reducing entity A (plastoquinone) beyond Q (the primary electron acceptor of pigment system II, PSII), or, of a high “S” state (charge accumulator) of oxygen evolving system; its intensity is dramatically reduced by low concentrations (1 μM) of DCMU, and, there is more of it in PSII than in PSI particles. (3) Peak II is due to reaction of Q‐ with the “S” states of the oxygen evolving system; its intensity increases upon the addition of low concentrations of DCMU, at the expense of peak I; it is most sensitive to mild heating, and there is more of it in PSII than in PSI particles. (4) Peak III was not studied here as it was not resolved in most of our preparations. (5) Peak IV is from both pigment system I and II; it is sensitive to heating (>50°C), is somewhat sensitive to DCMU, and is present in both PSI and PSII particles. (6) Peak V is from PSI; it is least sensitive to mild heating, and it is enriched in PSI particles. The present studies have extended our knowledge regarding the origin of glow peaks in spinach chloroplasts and Euglena cells; in particular, the involvement of the charge accumulating “S” states of oxygen evolution (for peaks I and II) and of system I (for peak V) are emphasized in this paper.

No abstract

Abstract— Spinach leaves and Euglena cells when frozen in light to 77 K emit light during slow warming in the dark to give 6 peaks. The peak appearing at 118 K is observed even after DCMU or heat treatment and also in aged chloroplasts that are inactive in electron transport. The data indicate that peaks appearing at 261 and 321 K are due to back reactions of primary acceptors of PS II and PS I respectively with oxidized chlorophylls. The DCMU sensitivity of Tl peaks at 283 and 298 K suggests that they are associated with the flow of electrons between PS II and PS I. Evidence has been presented to show that the PS 1 chlorophylls are involved in part of the luminescence observed during the temperature rise. A mechanism involving the return of the thermally detrapped electrons to the ground state of chlorophylls through their excited states has been proposed to explain some of the Tl peaks.

Pre-illumination of Chlorella cells at room temperature with light primarily absorbed by PSII (650 nm) produces a state called state II. This is characterized by high fluorescence at 715 nm (high F715/F685) at liquid nitrogen temperature. Alternately if the cells are pre-illuminated by light primarily absorbed by PSI (710 nm) then state I with high fluorescence at 685 nm (low F715/ F685) at 77K is produced. We have investigated the role of photophosphorylation in the development of state I/II in chlorella cells using uncoupler and energy transfer inhibitors. The results suggested that the development of state I depends upon the energization of the membrane. Both DCCD and TPTC which permit build up of proton gradient block the adaptation to state I in­ dicating that proton gradient formation alone is not sufficient to develop state I. The data obtain­ ed by us as also published in the literature indicate that redox states o f the electron transport carriers are responsible for the development of state II.