Oxygen-evolving system and secondary quinonic acceptors are highly reduced in dark adapted Euglena cells: A thermoluminescence study

Effects of NiO, SnO2, and Ni-doped SnO2 semiconductor metal oxides on the oxygen sensing capacity of H2TPP

Improving the performance of optical oxygen sensors can be accomplished by adding metal oxide semiconductors (MOSs) additives to the composition comprising an oxygen-sensing agent immobilized in a polymeric thin film. For several decades, MOSs have attracted great interest in gas sensors due to their high sensitivity to many target gasses. Herein, meso-tetraphenylporphyrin (H₂TPP) dye was immobilized into the poly(1-trimethylsilyl-1-propyne) (poly(TMSP)) silicone rubber in the presence of NiO, SnO₂, Ni:SnO₂ metal oxide particles as additives, and their thin films were prepared to investigate oxygen-sensitive optical chemical sensor properties. The characterizations of the synthesized metal oxide powders were carried out through XPS, XRD, FT-IR, PL spectroscopy and SEM methods. Intensity-based spectra and decay kinetics of H₂TPP-based thin films were investigated for the concentration range of 0%-100% [O₂]. The oxygen sensitivity (I₀/I₁₀₀) of the porphyrin was calculated as 70%. Whereas the relative signal intensity values of H₂TPP-based sensor slides were measured as 75%, 80%, and 88% in the presence of NiO, SnO₂, Ni:SnO₂ additives, respectively. The H₂TPP in combination with Ni:SnO₂ semiconductor provided a higher I₀/I₁₀₀ value, larger response range, higher Stern-Volmer constant (K_SV) value, and faster response time compared to the undoped form, and also NiO and SnO₂ additive-doped forms of H₂TPP. The response and the recovery times of the porphyrin-based sensing slide along with Ni:SnO₂ additives have been measured as 12 and 50 s. These results make the H₂TPP along with the MOSs promising candidates as oxygen probes.

The role of transmembrane electrochemical potential and phosphorylation of PS II proteins in temperature induced light emission from ATP-treated lettuce thylakoids

Changes in characteristics of flash-induced thermoluminescence (TL) glow curves in thylakoids of lettuce following incubation of the organelles with ATP, under illumination or in the dark, were investigated. TL bands were induced by 1 or 2 flashes fired at -10°C or 1°C in thylakoids: TL curves in control thylakoids which were dark-adapted or submitted to an illumination without ATP, can be deconvoluted as the sum of one single B band and minor contributions. In thylakoids incubated for 90 s with 0.5 mM ATP, either under light or in the dark (after a 90 s preillumination), bands presented complex shapes; after deconvolution, they appeared composed of a B band with a low Ea (activation energy): 0.6 e.v. as compared to 0.75 in control, and a supplementary band peaking at about 10°C. The band at low temperature was suppressed by low concentrations (10-20 nM) of valinomycin, nigericin or FCCP as well as by 10 mM ammonium chloride, leaving B bands with the same characteristics as in control material. Finally with higher nigericin concentrations, the bands became single B bands with high Ea (0.9 e.v.). These characteristics would define 3 different energized states (in the form of a transmembrane electrochemical potential) for thylakoids based upon the presence of the 10°C band and the value of the activation energy for the B band component. The presence of a large 10°C band was also correlated to the existence of a larger transmembrane pH gradient, in the dark, after an ATP-treatment, than in controls. The 10°C band was specifically suppressed by the action of low concentrations of alkaline phosphatase with minor changes in characteristics of the remaining B band suggesting that phosphorylation of PS II proteins is also involved in the appearance of this low temperature band. The main mechanism at the origin of the low temperature band would be a destabilization of S2/3QB (-) charge pairs in energized membranes.

Evolution of PS IIα and PS IIβ centers during the greening of Euglena gracilis Z: Correlations with changes in lipid content

The building up of the two types of reaction centers, PS IIα and PS IIβ, was investigated during the greening of Euglena gracilis Z cells in resting medium. The maximal values in the proportion of PS IIα centers (55%) and in the oxygen evolved per chlorophyll were reached at the outbreak of greening, when accumulation of galactolipids (MGDG and DGDG) rich in unsaturated fatty acids occurred, and when anionic lipids (SQDG and PG) emerged. As the greening progressed, the chlorophyll accumulation corresponded to a secondary enrichment in PS IIβ centers, which built up more rapidly than PS IIα centers; correlatively, a general saturation of the fatty acids constitutive of all lipid classes took place.

Compared thermoluminescence characteristics of pea thylakoids studied in vitro and in situ (in leaves). The effect of photoinhibitory treatments

Characteristics of thermoluminescence (TL) glow curves were studied in thylakoids (isolated from pea leaves) or in intact pea leaves after an exposure to very high light for 2 min in the TL device. The inhibition of photosynthesis was detected as decreases of oxygen evolution rates and/or of variable fluorescence.In thylakoids exposed to high light, then dark adapted for 5 min, a flash regime induced TL glow curves which can be interpreted as corresponding to special B bands since: 1) they can be fitted by a single B band (leaving a residual band at -5°C) with a lower activation energy and a shift of the peak maximum by -5 to -6°C and, 2) the pattern of oscillation of their amplitudes was normal with a period of 4 and maxima on flashes 2 and 6. During a 1 h dark adaptation, no recovery of PS II activity occurred but the shift of the peak maximum was decreased to -1 to -2°C, while the activation energy of B bands increased. It is supposed that centers which remained active after the photoinhibitory treatment were subjected to reversible and probably conformational changes.Conversely, in intact leaves exposed to high light and kept only some minutes in the dark, TL bands induced by a flash regime were composite and could be deconvoluted into a special B band peaking near 30°C and a complex band with maximum at 2-5°C. In the case of charging bands by one flash, this low temperature band was largely decreased in size after a 10 min dark adaptation period; parallely, an increase of the B band type component appeared. Whatever was the flash number, bands at 2-5°C were suppressed by a short far red illumination given during the dark adaptation period and only remained a main band a 20°C; therefore, the origin of the low temperature band was tentatively ascribed to recombinations in centers blocked in state S2QA (-)QB (2-). In vivo, the recovery of a moderately reduced state in the PQ pool, after an illumination, would be slow and under the dependence of a poising mechanism, probably involving an electron transfer between cytosol and chloroplasts or the so-called 'chlororespiration' process.