ON THE ORIGIN OF GLOW PEAKS IN EUGLENA CELLS, SPINACH CHLOROPLASTS AND SUBCHLOROPLAST FRAGMENTS ENRICHED IN SYSTEM I OR II

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.

Thermoluminescence in Chloroplast Thylakoid

“…This finding has been further corroborated by subsequent experimentation by several workers using bundle sheath chloroplasts of C-4 plants that apparently lack PSII and, therefore, show very weak TL. The inhibition of PSI activity by HgCl 2 does not affect the glow peak yield of isolated chloroplast (Sane et al, 1977;Horvath et al, 1978). Several other studies using herbicides and inhibitors that interact with PSI electron flow supports this conclusion.…”

“…Major TL bands are missing in etiolated leaves. Intermittent illumination to greening leaves which does not develop Mn clusture properly do not show the TL bands (Inoue et al, 1976;Sane et al, 1977). Misra et al (1998b) reported a gradual increase in the Q and B band from base to apex of that wheat leaves greening under continuous illumination, which confirms a developmental gradient across the wheat leaf lamina and a gradual development and organization of the photosynthetic PSII complexes.…”

TEMPERATURE DEPENDENCE OF DELAYED LIGHT EMISSION IN THE 6 to 340 MICROSECOND RANGE AFTER A SINGLE FLASH IN CHLOROPLASTS

“…Light emission can be obtained from preilluminated samples by slow heating [the glow curve technique (Arnold and Sherwood, 1957;Arnold and Azzi, 1968) with four or more bursts of emission at different temperatures (Shuvalov and Litvin, 1969;Arnold and Azzi, 1971;Desai et al, 1975;Sane et al, 1977)l. Rapid heating (temperature-jump) also causes preilluminated chloroplasts to emit a pulse of delayed light ; Jursinic and Govindjee, 1972;Malkin and Hardt, 1973).…”

Disorganization of the Mn4Ca complex of photosystem II by ruthenium red: a thermoluminescence study

“…Transformation of the B-band to Q-band occurs due to inhibition of electron transfer between Q A and Q B by DCMU, which enables the stabilization of Q A − as a negative charge detectable by TL instead of Q B − . Appearance of the Qband requires a functional water-splitting complex (40). Figure 2B shows the TL glow curves observed when 15 μM DCMU was added in control and RR-treated thylakoids.…”