The photoreduction of H(2)O(2) by Synechococcus sp. PCC 7942 and UTEX 625.
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It has been claimed that the sole H(2)O(2)-scavenging system in the cyanobacterium Synechococcus sp. PCC 7942 is a cytosolic catalase-peroxidase. We have measured in vivo activity of a light-dependent peroxidase in Synechococcus sp. PCC 7942 and UTEX 625. The addition of small amounts of H(2)O(2) (2.5 microM) to illuminated cells caused photochemical quenching (qP) of chlorophyll fluorescence that was relieved as the H(2)O(2) was consumed. The qP was maximal at about 50 microM H(2)O(2) with a Michaelis constant of about 7 microM. The H(2)O(2)-dependent qP strongly indicates that photoreduction can be involved in H(2)O(2) decomposition. Catalase-peroxidase activity was found to be almost completely inhibited by 10 microM NH(2)OH with no inhibition of the H(2)O(2)-dependent qP, which actually increased, presumably due to the light-dependent reaction now being the only route for H(2)O(2)-decomposition. When (18)O-labeled H(2)O(2) was presented to cells in the light there was an evolution of (16)O(2), indicative of H(2)(16)O oxidation by PS 2 and formation of photoreductant. In the dark (18)O(2) was evolved from added H(2)(18)O(2) as expected for decomposition by the catalase-peroxidase. This evolution was completely blocked by NH(2)OH, whereas the light-dependent evolution of (16)O(2) during H(2)(18)O(2) decomposition was unaffected. (+info)
A three-state model for energy trapping and chlorophyll fluorescence in photosystem II incorporating radical pair recombination.
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The multiphasic fluorescence induction kinetics upon a high intensity light pulse have been measured and analyzed at a time resolution of 10 micros in intact leaves of Peperomia metallica and Chenopodium album and in chloroplasts isolated from the latter. Current theories and models on the relation between chlorophyll fluorescence yield and primary photochemistry in photosystem II (PSII) are inadequate to describe changes in the initial phase of fluorescence induction and in the dark fluorescence level F(0) caused by pre-energization of the system with single turnover excitation(s). A novel model is presented, which gives a quantitative relation between the efficiencies of primary photochemistry, energy trapping, and radical pair recombination in PSII. The model takes into account that at least two turnovers are required for stationary closure of a reaction center. An open reaction center is transferred with high efficiency into its semiclosed (-open) state. This state is characterized by Q(A) and P680 in the fully reduced state and a lifetime equal to the inverse of the rate constant of Q(A)(-) oxidation (approx. 250 micros). The fluorescence yield of the system with 100% of the centers in the semiclosed state is 50% of the maximal yield with all centers in the closed state at fluorescence level F(m). A situation with approximately 100% of the centers in the semiclosed state is reached after a single turnover excitation in the presence of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU). The lifetime of this state under these conditions is approximately 10 s. Closure of a semiclosed (-open) center occurs with low efficiency in a second turnover. The low(er) efficiency is caused by the rate of P(+) reduction by the secondary donor Y(Z) being competitive with the rate of radical pair recombination in second and following turnovers. The single-turnover-induced alterations in the initial kinetics of the fluorescence concomitantly with a 15-25% increase in F(o) can be simulated with the present so called three-state model of energy trapping. The experimental data suggest evidence for an electrostatic effect of local charges in the vicinity of the reaction center affecting the rate of radical pair recombination in the reaction center. (+info)
Humboldt penguins outmanoeuvring El Nino.
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We satellite-tracked five Humboldt penguins during the strong 1997/98 El Nino Southern Oscillation (ENSO) from their breeding island Pan de Azucar (26 degrees 09'S, 70 degrees 40'W) in Northern Chile and related their activities at sea to satellite-derived information on sea surface temperature (SST), sea surface temperature anomaly (SSTA), wind direction and speed, chlorophyll a concentrations and statistical data on fishery landings. We found that Humboldt penguins migrated by up to 895 km as marine productivity decreased. The total daily dive duration was highly correlated with SSTA, ranging from 3.1 to 12.5 h when the water was at its warmest (+4 degrees C). Birds travelled between 2 and 116 km every day, travelling further when SSTA was highest. Diving depths (maximum 54 m), however, were not increased with respect to previous years. Two penguins migrated south and, independently of each other, located an area of high chlorophyll a concentration 150 km off the coast. Humboldt penguins seem to use day length, temperature gradients, wind direction and olfaction to adapt to changing environmental conditions and to find suitable feeding grounds. This makes Humboldt penguins biological in situ detectors of highly productive marine areas, with a potential use in the verification of trends detected by remote sensors on board satellites. (+info)
Ionic and osmotic effects of NaCl-induced inactivation of photosystems I and II in Synechococcus sp.
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We report here that osmotic effects and ionic effects are both involved in the NaCl-induced inactivation of the photosynthetic machinery in the cyanobacterium Synechococcus sp. PCC 7942. Incubation of the cyanobacterial cells in 0.5 M NaCl induced a rapid and reversible decline and subsequent slow and irreversible loss of the oxygen-evolving activity of photosystem (PS) II and the electron transport activity of PSI. An Na(+)-channel blocker protected both PSII and PSI against the slow, but not the rapid, inactivation. The rapid decline resembled the effect of 1.0 M sorbitol. The presence of both an Na(+)-channel blocker and a water-channel blocker protected PSI and PSII against the short- and long-term effects of NaCl. Salt stress also decreased cytoplasmic volume and this effect was enhanced by the Na(+)-channel blocker. Our observations suggested that NaCl had both osmotic and ionic effects. The osmotic effect decreased the amount of water in the cytosol, rapidly increasing the intracellular concentration of salts. The ionic effect was caused by an influx of Na(+) ions through potassium/Na(+) channels that also increased concentrations of salts in the cytosol and irreversibly inactivated PSI and PSII. (+info)
Elevated CO(2) induces biochemical and ultrastructural changes in leaves of the C(4) cereal sorghum.
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We analyzed the impact of growth at either 350 (ambient) or 700 (elevated) microL L(-1) CO(2) on key elements of the C(4) pathway (photosynthesis, carbon isotope discrimination, and leaf anatomy) using the C(4) cereal sorghum (Sorghum bicolor L. Moench.). Gas-exchange analysis of the CO(2) response of photosynthesis indicated that both carboxylation efficiency and the CO(2) saturated rate of photosynthesis were lower in plants grown at elevated relative to ambient CO(2). This was accompanied by a 49% reduction in the phosphoenolpyruvate carboxylase content of leaves (area basis) in the elevated CO(2)-grown plants, but no change in Rubisco content. Despite the lower phosphoenolpyruvate carboxylase content, there was a 3-fold increase in C isotope discrimination in leaves of plants grown at elevated CO(2) and bundle sheath leakiness was estimated to be 24% and 33%, respectively, for the ambient and elevated CO(2)-grown plants. However, we could detect no difference in quantum yield. The ratio of quantum yield of CO(2) fixation to PSII efficiency was lower in plants grown at elevated CO(2), but only when leaf internal was below 50 microL L(-1). This suggests a reduction in the efficiency of the C(4) cycle when [CO(2)] is low, and also implies increased electron transport to acceptors other than CO(2). Analysis of leaf sections using a transmission electron microscope indicated a 2-fold decrease in the thickness of the bundle sheath cell walls in plants grown at elevated relative to ambient CO(2). These results suggest that significant acclimation to increased CO(2) concentrations occurs in sorghum. (+info)
Two types of functionally distinct NAD(P)H dehydrogenases in Synechocystis sp. strain PCC6803.
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The ndhD gene encodes a membrane protein component of NAD(P)H dehydrogenase. The genome of Synechocystis sp. PCC6803 contains 6 ndhD genes. Three mutants were constructed by disrupting highly homologous ndhD genes in pairs. Only the DeltandhD1/DeltandhD2 (DeltandhD1/D2) mutant was unable to grow under photoheterotrophic conditions and exhibited low respiration rate, although the mutant grew normally under photoautotrophic conditions in air. The DeltandhD3/DeltandhD4 (DeltandhD3/D4) mutant grew very slowly in air and did not take up CO(2). The results demonstrated the presence of two types of functionally distinct NAD(P)H dehydrogenases in Synechocystis PCC6803 cells. TheDeltandhD5/DeltandhD6 (DeltandhD5/D6) mutant grew like the wild-type strain. Under far-red light (>710 nm), the level of P700(+) was high in DeltandhD1/D2 and M55 (ndhB-less mutant) at low intensities. The capacity of Q(A) (tightly bound plastoquinone) reduction by plastoquinone pool, as measured by the fluorescence increase in darkness upon addition of KCN, was much less in DeltandhD1/D2 and M55 than in DeltandhD3/D4 and DeltandhD5/D6. We conclude that electrons from NADPH are transferred to the plastoquinone pool mainly by the NdhD1.NdhD2 type of NAD(P)H dehydrogenases. (+info)
Genetic analyses of two independent chlorophyll-deficient mutants identified among the progeny of a single chimeric foliage soybean plant.
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Chimeric (variegated) foliage plants are frequently observed in many species. In soybean [Glycine max(L.) Merr.], progeny of chimeric plants are a source of nuclear and cytoplasmically inherited mutants. Self-pollinated progeny of a single chimeric plant derived from tissue culture of PI 427099 (Jilin 3) included plants with green foliage, chimeric foliage, yellow foliage (viable), and yellow foliage (lethal). Our objectives were to determine (1) inheritance, linkage, and allelism of the lethal-yellow mutant with known chlorophyll-deficient mutants; (2) inheritance, linkage, and allelism of the viable-yellow mutant with known chlorophyll-deficient mutants; (3) allelism of the lethal-yellow mutant with the viable-yellow mutant; and (4) male and female gamete transmission of the viable-yellow mutant trait. The viable-yellow mutant was allelic to T323, y20 y20 (Ames 2) Mdh1-n Mdh1-n (Ames 2) and was assigned genetic type collection number T361 and gene symbol y20 y20 (Ames 24) Mdh1-n Mdh1-n (Ames 22). The lethal-yellow mutant was allelic to T225H (Y18 y18) and was assigned genetic type collection number T362H and gene symbol Y18 y18 (Ames 2). T225H became Y18 y18 (Ames 1). The two chlorophyll-deficient mutants were not linked to each other. There was no significant difference in F(1) male or female gamete transmission of the viable-yellow mutant. However, many cross-combinations gave significant deviations from the expected 3 green plants:1 viable-yellow plant in the F(2) generation. The allelism of these two chlorophyll-deficient mutants with mutants T225H and T323, derived from putative transposable element systems, is intriguing. An explanation of this phenomenon awaits molecular experimentation. (+info)
Decay kinetics and quantum yields of fluorescence in photosystem I from Synechococcus elongatus with P700 in the reduced and oxidized state: are the kinetics of excited state decay trap-limited or transfer-limited?
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Transfer and trapping of excitation energy in photosystem I (PS I) trimers isolated from Synechococcus elongatus have been studied by an approach combining fluorescence induction experiments with picosecond time-resolved fluorescence measurements, both at room temperature (RT) and at low temperature (5 K). Special attention was paid to the influence of the oxidation state of the primary electron donor P700. A fluorescence induction effect has been observed, showing a approximately 12% increase in fluorescence quantum yield upon P700 oxidation at RT, whereas at temperatures below 160 K oxidation of P700 leads to a decrease in fluorescence quantum yield ( approximately 50% at 5 K). The fluorescence quantum yield for open PS I (with P700 reduced) at 5 K is increased by approximately 20-fold and that for closed PS I (with P700 oxidized) is increased by approximately 10-fold, as compared to RT. Picosecond fluorescence decay kinetics at RT reveal a difference in lifetime of the main decay component: 34 +/- 1 ps for open PS I and 37 +/- 1 ps for closed PS I. At 5 K the fluorescence yield is mainly associated with long-lived components (lifetimes of 401 ps and 1.5 ns in closed PS I and of 377 ps, 1.3 ns, and 4.1 ns in samples containing approximately 50% open and 50% closed PS I). The spectra associated with energy transfer and the steady-state emission spectra suggest that the excitation energy is not completely thermally equilibrated over the core-antenna-RC complex before being trapped. Structure-based modeling indicates that the so-called red antenna pigments (A708 and A720, i.e., those with absorption maxima at 708 nm and 720 nm, respectively) play a decisive role in the observed fluorescence kinetics. The A720 are preferentially located at the periphery of the PS I core-antenna-RC complex; the A708 must essentially connect the A720 to the reaction center. The excited-state decay kinetics turn out to be neither purely trap limited nor purely transfer (to the trap) limited, but seem to be rather balanced. (+info)