Adenine complexes of thymine and uracil: electron spin resonance and thermoluminescence investigations

Electron spin resonance (E.S.R.) and thermoluminescence (T1) studies following irradiation with high-energy electrons and 60Co λ-rays have been carried out at room temperature and at low (77°Κ) temperature. Adenine, thymine and uracil and their two equimolecular complexes, adenine-thymine and adenine-uracil, have been used in these investigations. E.S.R. measurements at room temperature showed that the complexes were more resistant to radiation, and the differences in the free-radical yields of the complexes on the one hand, and their constituents on the other, follow dose-response patterns that are specific to the complexes. Low-temperature E.S.R. measurements carried out before and after T1 have indicated that the E.S.R. signal originates in at least two groups of electrons, probably only one of which is active for T1. These studies also show that the modes of transfer of radiation damage in the two complexes are different. These results are further substantiated by quantitative measurements on the photo-bleaching characteristics of thermoluminescence of the samples

Characterization of the low temperature thermoluminescence band Z<SUB>v</SUB> in leaf an explanation for its variable nature

Out of the six thermoluminescence bands reported for a mature leaf, one band (Z<SUB>v</SUB>) appearing at the lowest temperatures is dependent on the temperature of illumination. The characteristics of this band in fresh leaf are compared with those in a leaf heated to 60&#176; C for 5 min. It is concluded here that this band, following illumination at temperatures lower than 173 K, is part of Arnold and Azzi's Z band (Arnold, W. and Azzi, J.R. (1971) Photochem. Photobiol. 14, 233-240). However, it is a part of peak I when observed subsequent to illumination beyond 173 K. An explanation for the appearance of this band at different temperatures is proposed

Isothermal luminescence and thermo-luminescence of nucleic acid bases following γ -irradiation

The emission spectra of radiation induced isothermal luminescence (ITL) and the thermolu-minescence (TL) of purines and pyrimidines of nucleic acids and analogue 6-azauracil in the form of pellets of dry polycrystalline powders have been studied at 77 K, and compared with their low temperature fluorescence and phosphorescence spectra. The qualitative and quantitative measurements of isothermal luminescence and thermoluminescence show that the two result from the same radiative transitions. The thermoluminescence emission was observed to coincide with the phosphorescence emission of the compounds in all the cases. The thermoluminescence of the pyrimidines and their analogue, however, have shown an additional component corresponding to their fluorescence in the ultraviolet region. An extension of the Weissbluth model based on the location of the electron traps in relation to the excited states of the compounds is proposed to explain their thermoluminescence emission

Thermoluminescence studies on spinach leaves and euglena

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

Pergamon Press. Printed In Great Britain A NEW GLOW PEAK, IN RHODOPSEUDOMONAS SPHAEROIDES

Abstract-A new glow peak at 120 K has been observed in Rhodopseudomanas sphaeroides and in its carotenoidless green mutant. This peak (labelled Zn), which is composed of two peaks at 120 and 150 K, appears when the bacteria are illuminated with white light while being cooled to 77 K and then warmed in darkness at a heating rate of 10 K per min. Delayed light emission and prompt fluorescence spectra show peaks around 530, 610 and 660 nm. The action spectra of light emission show a major peak at 410 nm and a smaller peak around 545 nm. The pigment responsible for the light emission is also leached out in the suspension medium. The chromophore responsible for the light emission appears to be magnesium protoporphyrin IX, not bacteriochlorophyll

On the origin ofglow peaks in euglena cells, spinach chloroplasts and subchloroplast fragments enriched in system I or II

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 μ M) 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 (&gt;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

Microspectrophotometric studies on the pigments in vivo of single algal cells-I. Pigments of Chlorella Pyrenoidosa

The pigments in vivo of single cells of Chlorella pyrenoidosa were studied by the microspectrophotometric technique. An accessory recording the first derivative of absorption was used to obtain fine resolution and enhanced accuracy. The results suggest that there are several long-wavelength components of Chl a in vivo. In addition, there seem to be four short-wave forms of Chl a. It is also likely that Chl b exists in vivo in two different forms. The existence of all these forms was demonstrated at room temperature

Derivative microspectrophotometry of single cells in vivo

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Identification of far-red-induced relative increase in the decay of delayed light emission from photosynthetic membranes with thermoluminescence peak V appearing at 321 K

The relative increase in the decay of delayed light emission from photosynthetic membranes following far-red light excitation is shown to be related to thermoluminescence peak V appearing at 321 K. Peak V and the relative increase in the decay of delayed light emission show parallel changes in their intensities following far-red excitation