Comparative EPR and thermoluminescence study of anoxic photoinhibition in Photosystem II particles

Photosystem II particles were exposed to 800 W m^–2 white light at 20 °C under anoxic conditions. The F_o level of fluorescence was considerably enhanced indicating formation of stable-reduced forms of the primary quinone electron acceptor, Q_A. The F_m level of fluorescence declined only a little. The g=1.9 and g=1.82 EPR forms characteristic of the bicarbonate-bound and bicarbonate-depleted semiquinone-iron complex, Q_A ^–Fe²⁺, respectively, exhibited differential sensitivity against photoinhibition. The large g=1.9 signal was rapidly diminished but the small g=1.82 signal decreased more slowly. The S₂-state multiline signal, the oxygen evolution and photooxidation of the high potential form of cytochrome b-559 were inhibited approximately with the same kinetics as the g=1.9 signal. The low potential form of oxidized cytochrome b-559 and Signal II_slow arising from Tyr_D ⁺ decreased considerably slower than the g=1.9 semiquinone-iron signal. The high potential form of oxidized cytochrome b-559 was diminished faster than the low potential form. Photoinhibition of the g=1.9 and g=1.82 forms of Q_A was accompanied with the appearance and gradual saturation of the spin-polarized triplet signal of P 680. The amplitude of the radical signal from photoreducible pheophytin remained constant during the 3 hour illumination period. In the thermoluminescence glow curves of particles the Q band (S₂Q_A ^– charge recombination) was almost completely abolished. To the contrary, the C band (Tyr_D ⁺Q_A ^– charge recombination) increased a little upon illumination. The EPR and thermoluminescence observations suggest that the Photosystem II reaction centers can be classified into two groups with different susceptibility against photoinhibition.Abbreviations C band thermoluminescence band associated with Tyr-D⁺Q _a ^– charge recombination - Chl chlorophyll - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - EPR electron paramagnetic resonance - F_o initial fluorescence - F_m maximum fluorescence - Q band thermoluminescence band originating from S₂Q _a -charge recombination - Q _a the primary quinone electron acceptor of PS II - P 680 the primary electron donor chlorophyll of PS II - S₂ oxidation state of the water-splitting system - Phe pheophytin - TL thermoluminescence - Tyr _d redox active tyrosine-160 of the D₂ protein     

The effect of fish and aquatic habitat complexity on amphibians

Fish introductions are considered one of the most widespread anthropogenic threats to aquatic ecosystems. Their negative impact on native amphibian communities has received increasing attention in recent years. We investigated the relationship between the introduced fish, emergent vegetation cover and native amphibians in man-made ponds generated by regulation and dam building along the Tarnava Mare Valley (Romania) during the last 40 years. We inventoried amphibians and fish inhabiting 85 permanent ponds and estimated habitat complexity focusing on emergent vegetation cover. Four amphibian species were found to be negatively associated with the presence of predatory fish. Species richness of ponds without fish and ponds without predatory fish did not differ significantly, whereas ponds containing only predatory fish had significantly lower amphibian richness. A significant positive relationship was found between the emergent vegetation cover and pond occupancy of six amphibian species and amphibian species richness. As a management recommendation, we suggest the restriction of fish introductions to non predatory fish and the maintenance of high emergent vegetation cover in the ponds. Handling editor: S. Declerck     

Late Upper Pleistocene human peopling of the Far East: multivariate analysis and geographic patterns of variation

This research deals with the History of the human peopling of Far East Asia during the Late Upper Pleistocene. It brings some new answers to the question of modern human migrations in the Far East. This study is based on morphometric analysis of 45 fossil crania. The results of the multivariate analyses, combined with the recognition of geographic patterns of variation, separate the fossils into three morphological classes. These three clusters enable us to propose a likely scenario for the human peopling of the Far East from about 67 000 years ago. To cite this article: F. Demeter et al., C. R. Palevol 2 (2003).     

Elemental analysis of samples of biological origin relative to their protein content by means of charged particle bombardment

The particle-induced X-ray emission (PIXE) method and the 14N(d,p)15N nuclear reaction are combined for simultaneous trace element and nitrogen determination. Measurement of nitrogen content often allows the relating of the elemental concentrations determined by PIXE to the protein content of the sample. For the measurements only a small amount of sample material is needed; therefore, it is possible to keep track of the quantity of a certain element in the successive steps of a biomedical separation process. In about 10 min, trace element concentrations in the ppm range can be determined with a statistical accuracy of about 10%.     

Flash oxygen yield patterns of autotrophically and photoheterotrophically grown Chlamydobotrys stellata in the presence and absence of lipophilic acceptors

The obligate phototrophic green alga Chlamydobotrys stellata does not evolve oxygen when grown in CO₂-free atmosphere on acetate. With the application of the lipophilic acceptor 2,6-dichloro-p-benzoquinone it was investigated whether this phenomenon is caused by the inactivation of the water-splitting system or by an inhibition of the electron transport chain. It was found that in the presence of DCQ, the photoheterotrophic alga exhibited a normal period-4 flash oxygen pattern, but the steady state yield was only 25% of that measured in the autotrophic cells. After DCQ addition, the initial distribution of S-states and the values of the transition probabilities proved to be the same in the autotrophic and photoheterotrophic algae. These results indicate that photoheterotrophic growth conditions inhibit the electron transport of Chl. stellata behind the acceptor site of DCQ, but the water-splitting system remains active with a reduced oxygen evolving capacity.Abbreviations Chl chlorophyll - DCQ 2,6-dichloro-p-benzoquinone - DCMU 3-(3,4)-dichlorophenyl)-1,1-dimethylurea - DBMIB 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone - pBQ 1,4-benzoquinone - PS I photosystem I - PS II photosystem II