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Oat (Avena sativa) plants were grown in the field near the urban area of Valencia, Eastern Spain. The data on air quality showed that ozone was the main phytotoxic pollutant present in ambient air reaching a 7-h mean of 46 nl l(-1) and a maximum hourly peak of 322 nl l(-1). The effect of ambient ozone on PSII activity was examined by measurements of chlorophyll (Chl) a fluorescence. In leaves with visible symptoms, the function of PSII was changed at high actinic irradiances. Nonphotochemical quenching (NPQ) was higher and quantum efficiency of PSII (Phi(PSII)), photochemical quenching (q(p)), quantum efficiency of excitation capture and PSII electron flow (F(v)'/F(m)') were lower. An enhanced susceptibility to photoinhibition was observed for symptom-exhibiting leaves compared to leaves that remain free of visible symptoms. Both the lowering of photosynthesis efficiency and the increased sensitivity to photoinhibition probably contribute to reduced crop yield in the field, to different extents, depending on growth conditions. To our knowledge, this is the first report that demonstrates that quantum efficiency of exciton trapping in PSII is associated with foliar injury in oat leaves in response to ambient concentration of ozone.

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An immortal, cloned cell line (RCMH), obtained from human skeletal muscle was established in our laboratory and shown to express muscle specific proteins. We measured ligand binding to ion channels, ion currents using whole cell patch clamp and intracellular calcium both in cells grown in complete media and in cells grown for 4-40 days in media supplemented with hormones and nutrients (differentiating media). Markers for differentiated muscle, such as the muscle isoform of creatine kinase and the cytoskeletal proteins alpha-actinin, alpha-sarcomeric actin, myosin and titin were present in early stages. Receptors for gamma toxin from Tityus serrulatus scorpion venom, a specific modulator for voltage dependent sodium channels, were present (0.9-1.0 pmol mg-1 protein) during stage 1 (0-6 days in culture with differentiating media) and increased by 50% in stage 3 (more than 10 days in differentiating media). High and low affinity dihydropyridine receptors present in stage 1 convert into a single type of high affinity receptors in stage 3. Both intracellular calcium release and InsP3 receptors were evident in stage 1 but ryanodine receptors were expressed only in stage 3. RCMH cells showed no voltage sensitive currents in stage 1. Between 7 and 10 days in differentiating media (stage 2), an outward potassium current was observed. Small inward currents appeared only in stage 3; we identified both tetrodotoxin sensitive and tetrodotoxin resistant sodium currents as well as calcium currents. This pattern is consistent with the expression of voltage dependent calcium release before appearance of both the action potential and ryanodine receptors.

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A cell line (RCMH) in permanent culture was established from surgically removed adult normal human skeletal muscle by exposure to conditioned media obtained from thyroid cells. Cells proliferated indefinitely but displayed density inhibition of growth while maintaining some differentiated markers. Under certain incubation conditions, cells fused into myotube-like structures, with a concomitant increase in muscle specific proteins, such as human myoglobin, skeletal muscle myosin, desmin and dystrophin, as identified using immunocytochemical procedures. In addition, RCMH cells displayed high affinity receptors for alpha-bungarotoxin (Bmax = 0.7 pmol/mg protein, Kd = 1.5 nM) and dihydropyridines (Bmax = 0.3 pmol/mg protein, Kd = 0.5 nM for [3H]PN200-110); these values are comparable to those reported for muscle cells in primary culture. Patch-clamp studies showed the presence of 42 pS carbachol gated channels and of 5 pS calcium channels (current carried by barium); chloride and potassium channels were also seen. This new cell line appears to be a convenient model system to study skeletal muscle function.

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Zea mays L. cv INRA 5a coleoptile segments ecidify the incubation medium on the addition of 1-naphthyl acetate (1-NA). The buffering capacity of the bathing solution increases during 1-NA stimulated medium acidification. The solution bathing the 1-NA treated coleoptile segment was analyzed by high performance liquid chromatography. A considerable amount of acetic acid was detected in the bathing solution used to measure 1-NA-dependent medium acidification. For the first time, the data demonstrate directly the release of acetic acid from 1-NA. The extent of medium acidification was proportional to 1-NA concentration. Simultaneous measurement of medium acidification and acetate content upon addition of 1-NA showed that both processes were temporally correlated. The stoichiometry of proton equivalents to acetate ion was 0.966. Addition of 50 micromolar N,N'-dicyclohexylcarbodiimide had little effect on 1-NA-dependent medium acidification. The results indicate that 1-NA is hydrolyzed in the extracellular space of coleoptile cells.

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The content of cytochrome c-420 in Rhodospirillum rubrum chromatophores prepared by grinding with alumina is 5--10% of that in whole cells, and 20--40% in chromatophores by 'French' pressing. Flash-induced phosphorylation of various chromatophores which varied in cytochrome content from 7 to 40% is proportional to the cytochrome content. Extrapolating the cytochrome c-420 content to that observed in whole cells, a ratio ATP/P+X- near 1 is calculated. At low flash intensity the phosphorylation per flash is proportional to flash energy. Photophosphorylation in flashes given after a time of several minutes is only slightly dependent on the number of flashes. If the flashes are spaced from 0.1 to 10 s, relative phosphorylation in the first flash is about 70% and in the second 90+ of that observed in the following flashes. Proton binding is not affected by the cytochrome c-420 content and a ratio of H+/P+x- of 2.3 was found. These results can be explained by a working hypothesis in which charge separation occurring at one reaction centre and the resulting electron transport mediated amongst others by c-420, results in the injection of two protons into an ATPase, this in contrast to a chemiosmotic mechanism, where the protons are released in the chromatophore inner space.

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The aerobic photooxidations of reduced 2,6-dichlorophenolindophenol and of reaction-center bacteriochlorophyll (P-870) have been investigated in membrane vesicles (chromatophores) isolated from a non-phototrophic Rhodospirillum rubrum strain. In aerobic suspensions of wild-type chromatophores, continuous light elicits an increase of the levels of 2,6-dichlorophenolindophenol and of oxidized P-870, which reach steady-state values shortly after the onset of illumination. In contrast, light induces in mutant suspensions a transient increase of the levels of 2,6-dichlorophenol-indophenol and of oxidized P-870, which fall to low steady-state values within a few seconds. These observations suggest that the mutation has altered a redox constituent located on the low-potential side of the photochemical reaction center, between a pool of acceptors and oxygen. Since endogenous cyclic photophosphorylation is catalyzed by mutant chromatophores at normal rates, it appears that the constituent altered by the mutation does not belong to the cyclic electron-transfer chain responsible for photophosphorylation. However, the system which mediates the aerobic photooxidations and the cyclic system are not completely independent: endogenous photophosphorylation is inhibited by oxygen in wild-type chromatophores but not in mutant chromatophores; in addition, the inhibitor of cyclic electron flow, 2-heptyl-4-hydroxyquinoline-N-oxide, enhances the aerobic photooxidation of reduced 2,6-dichlorophenolindophenol by chromatophores from both strains. These results support a tentative branched model for light-driven electron transfer. In that model, the constituent altered in the mutant strain is located in a side electron-transfer chain which connects the cyclic acceptors to oxygen.

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Anaerobic suspensions of Rhodospirillum rubrum cells which had been grown in the dark under low oxygen tension showed only a small increase of their ATP content when illuminated for 30 s. The same suspensions failed to start immediate growth in the light. Both high light-induced ATP levels and immediate phototrophic growth were elicited by small amounts of oxygen which were insufficient by themselves to raise the ATP levels or to support growth in the dark. The oxygen requirement for growth disappeared after some time of anaerobic illumination and was not observed in suspensions of cells which had been grown in the light under anaerobiosis. Furthermore, these phototrophic cells reached the maximum levels of ATP when illuminated in the absence of oxygen. Strain F11, a mutant derivative of Rhodospirillum rubrum which lacked the ability to photoreduce oxygen in vitro, needed abnormally high amounts of oxygen to increase its ATP levels and to grow in the light. Besides, KCN inhibited the increase of ATP levels in illuminated mutant cells but not in wild type cells. An additional difference between both strains was that the oxygen requirement for growth did not disappear in the mutant after some time of anaerobic incubation in the light. To explain these observations, it is proposed that the photosynthetic system of semiaerobically-grown Rhodospirillum rubrum becomes overreduced under anaerobiosis. The oxygen-photoreducing system, which is impaired in the mutant is apparently used to oxidize the photosynthetic system to its optimal redox state, carrying electrons to oxygen or to other endogenous acceptors which are formed during incubation in the light. The mutant seems to replace the defective system by a cyanide-sensitive pathway which may reduce oxygen but not the alternative endogenous acceptors.

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The oxygen uptake which is observed when Rhodospirillum rubrum chromatophores are illuminated under air and in the presence of reduced 2, 6-dichlorophenolindophenol (DCIP), 2, 3, 5, 6-tetra-methyl-P-phenylenediamine (diaminodurene, DAD) or N, N'-tetramethyl-p-phenylenediamine (TMDP) depends on the electron-donor concentration according to the equation of Michaelis-Menten. The apparent Km for the donor is lowered by the electron-transfer inhibitor 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) which causes therefore a stimulation of the rate of the reaction at non-saturating concentrations of the donors. In contrast, the ATP formation which takes place simultaneously to oxygen uptake does not show an enzyme-like dependence on donor concentration. Moreover it is inhibited by HQNO to a variable extent, depending on the particular donor present and on its concentration. Therefore it appears that the HQNO-sensitive phosphorylation is coupled to a cyclic flow which coexists and competes with the non-cyclic flow from donor to oxygen. In the presence of HQNO, substrates and uncouplers of ATP formation accelerate somewhat the rate of the oxygen uptake supported by reduced DCIP and DAD. Thus part of the HQNO-resistant phosphorylation seems to be associated with the non-cyclic flow from those tow donors to oxygen. The lack of stimulation by phosphorylation or by uncoupling of the TMPD-supported oxygen uptake does not permit a conclusion as to whether this reaction is coupled to ATP formation or not. Another part of the HQNO-resistant ATP formation is independent of the presence of oxygen and appears to be associated to cyclic flows which bypass the HQNO site. This type of phosphorylation is most important in the presence of TMPD.

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