Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Diuron”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 883 records · Page 49Linked to original sources
PubMed1998

Model for the fluorescence induction curve of photoinhibited thylakoids.

The fluorescence induction curve of photoinhibited thylakoids measured in the presence of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea was modeled using an extension of the model of Lavergne and Trissl (Biophys. J. 68:2474-2492), which takes into account the reversible exciton trapping by photosystem II (PSII) reaction centers and exciton exchange between PSII units. The model of Trissl and Lavergne was modified by assuming that PSII consists of photosynthetically active and photoinhibited (inactive in oxygen evolution) units and that the inactive PSII units can efficiently dissipate energy even if they still retain the capacity for the charge separation reaction. Comparison of theoretical and experimental fluorescence induction curves of thylakoids, which had been subjected to strong light in the presence of the uncoupler nigericin, suggests connectivity between the photoinhibited and active PSII units. The model predicts that photoinhibition lowers the yield of radical pair formation in the remaining active PSII centers. However, the kinetics of PSII inactivation in nigericin-treated thylakoids upon exposure to photoinhibitory light ranging from 185 to 2650 micromol photons m-2 s-1 was strictly exponential. This may suggest that photoinhibition occurs independently of the primary electron transfer reactions of PSII or that increased production of harmful substances by photoinhibited PSII units compensates for the protection afforded by the quenching of excitation energy in photoinhibited centers.

Biophysical Phenomena↗
PubMed2000

Evidence for the presence of a component of the Mn complex of the photosystem II reaction centre which is exposed to water in the S(2) state of the water oxidation complex.

The interaction of water oxidising photosystem II preparations with the aqueous environment has been investigated using electron spin echo envelope modulation spectroscopy in the presence of 2H(2)O. The spectra show interaction of 2H of 2H(2)O with the preparation in the S(2) state. The component interacting with water decays during 1-4 weeks storage at 77 K. No interaction of water with the classical multiline S(2) Mn signal, which is more stable on storage at 77 K, was detected. The results show that a component of the water oxidation complex, possibly involving the Mn centre, is accessible to water and may be the water binding site for photosynthetic water oxidation.

Binding Sites↗
PubMed2001

Leucine and its keto acid enhance the coordinated expression of genes for branched-chain amino acid catabolism in Arabidopsis under sugar starvation.

Branched-chain alpha-keto acid dehydrogenase (BCKDH), a multienzyme complex, plays a key role in branched-chain amino acid catabolism. However, it remains unclear whether expression of each subunit is coordinately regulated in plants, which should be important for the efficient assembly of subunits into a functional multienzyme complex. We show that the transcripts from the Arabidopsis E1alpha subunit gene accumulated in dark-adapted leaves and in sugar-starved suspension cells. These results are complementary to our previous report that the transcripts for the E1beta and E2 subunit genes accumulated in sugar-starved cells. Expression of the E1alpha gene is likely to be regulated by hexokinase-mediated sugar signaling, indicating that sugar plays a regulatory role in the coordinated expression of BCKDH subunit genes. Furthermore, Leu and its metabolite alpha-ketoisocaproate have synergistic effects on the enhanced expression of BCKDH subunit genes under sugar starvation. We hence suggest that branched-chain amino acids activate their own degradation pathway in sugar-starved cells through co-induction of each subunit gene of BCKDH.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed2002

Singlet oxygen production in herbicide-treated photosystem II.

Photo-generated reactive oxygen species in herbicide-treated photosystem II were investigated by spin-trapping. While the production of .OH and O2-* was herbicide-independent, 1O2 with a phenolic was twice that with a urea herbicide. This correlates with the reported influence of these herbicides on the redox properties of the semiquinone QA-* and fits with the hypothesis that 1O2 is produced by charge recombination reactions that are stimulated by herbicide binding and modulated by the nature of the herbicide. When phenolic herbicides are bound, charge recombination at the level of P+*Pheo-* is thermodynamically favoured forming a chlorophyll triplet and hence 1O2. With urea herbicides this pathway is less favourable.

Binding Sites↗
PubMed2003

EPR study of light-induced regulation of photosynthetic electron transport in Synechocystis sp. strain PCC 6803.

The kinetics of the light-induced redox changes of the photosystem 1 (PS 1) primary donor P(700) in whole cells of the cyanobacteria Synechocystis sp. PCC 6803 were studied by the electron paramagnetic resonance method. It was shown that the linear photosynthetic electron transport in cyanobacteria was controlled by two main mechanisms: (i) oxygen-dependent acceleration of electron transfer from PS 1 to NADP(+) due to activation of the Calvin cycle reactions and (ii) retardation of electron flow between two photosystems governed by a transmembrane proton gradient. In addition to the linear photosynthetic electron transport, cyanobacteria were capable of maintaining alternative pathways involving cyclic electron transfer around PS 1 and respiratory chains.

Anti-Bacterial Agents↗
PubMed2003

Antagonistic dark/light-induced SigB/SigD, group 2 sigma factors, expression through redox potential and their roles in cyanobacteria.

The expression of group 2 sigma factors is characterized in a cyanobacterium Synechocystis sp. PCC 6803 grown in culture, changing light conditions (white, red and blue light, and darkness), or the presence of drugs (rifampicin, chloramphenicol, DCMU, and DBMIB), and the roles of these sigma factors are elucidated. The expression of dark/light-induced SigB/SigD was accelerated under opposite redox (oxidation/reduction) states in an electron transport chain of photosynthesis. Expression of the dark-induced lrtA and light-induced psbA2/3 transcript was significantly reduced in the sigB and sigD knockout strains, respectively. Abundant amounts of sigB transcript and protein were observed in the sigC knockout strain, implying that SigC represses SigB expression under light. These findings clearly showed that SigB/SigD with another group 2 sigma, SigC, contribute to transcription for a subset of dark/light-responsive genes in the cyanobacterium. A possible model for SigB/SigD is presented and the potential ability for promoter recognition is also discussed.

Bacterial Proteins↗
PubMed1997

Light-harvesting in Acaryochloris marina--spectroscopic characterization of a chlorophyll d-dominated photosynthetic antenna system.

Oxygenic photosynthesis of the prokaryote Acaryochloris marina involves chlorophyll d (Chl d) as the major pigment [Miyashita et al. (1996) Nature 383, 402]. Four spectral forms of Chl d (peak wavelengths: 694, 714, 726 and 740 nm) are resolvable by low-temperature absorption spectroscopy on intact cells. Based on fluorescence spectra (at 290 K and 77 K) and on analysis of fluorescence induction curves we conclude: (1) excitation energy is efficiently transferred between the various spectral forms of Chl d and the PS II reaction center; (2) Chl d serves as a light-harvesting pigment for both, Photosystem II (PS II) and PS I; (3) excitation energy transfer between PS II units occurs.

Chlorophyll↗
PubMed1997

Evidence for light-dependent and light-independent protein dephosphorylation in chloroplasts.

A number of photosystem II (PSII) associated proteins, including core proteins D1, D2 and CP43, and several proteins of the LHCII complex, are phosphorylated by a thylakoid-bound, redox-regulated kinase(s). We demonstrate here that the compound propyl gallate is an effective inhibitor of LHCII phosphorylation in vivo while having little effect on PSII core protein phosphorylation. Using this inhibitor, we demonstrate that LHCII dephosphorylation is insensitive to light in vivo. Taken together with our previous conclusion (Elich et al., EMBO J. 12 (1993) 4857-4862) that PSII core protein dephosphorylation is light-stimulated, our data suggest the presence of multiple phosphatases responsible for thylakoid protein dephosphorylation in vivo.

Cells, Cultured↗
PubMed1998

Exposure of Synechocystis 6803 cells to series of single turnover flashes increases the psbA transcript level by activating transcription and down-regulating psbA mRNA degradation.

Exposure of Synechocystis sp. PCC 6803 cells to series of single turnover flashes increases specifically the level of psbA and psbD2 messages, encoding the D1 and D2 proteins of photosystem II, as compared to light exposed cells. This increase is due to maintenance the transcription rate as high as in growth light and to the down-regulation of transcript degradation as in darkness. Inhibition of the plastoquinone pool reduction by DCMU or its oxidation by DBMIB does not diminish the transcription of the psbA gene under growth conditions. However, the degradation rate of psbA transcript, as well as of other transcripts encoding proteins of thylakoid complexes, is down-regulated in all conditions leading to the oxidation of the plastoquinone pool. We conclude that single turnover flashes are sensed as 'light' by transcription machinery of the cells irrespective of the plastoquinone pool reduction state and as 'dark' by the transcript degradation system.

Cyanobacteria↗
PubMed1999

Voltammetric detection of superoxide production by photosystem II.

Oxygen radicals play both pathological and physiological roles in biological systems. The detection of such radicals is difficult due to their transient nature and the presence of highly efficient antioxidant mechanisms. In plants the physiological role of oxygen is twofold, oxygen is produced by the oxidation of water and consumed as an electron acceptor. The direct involvement of oxygen in photosynthetic events exposes the photosynthetic apparatus to a high probability of damage by oxygen radicals. We report here a direct, simple and rapid method for the measurement of superoxide in vitro based on voltammetric detection. It has potential applications for other in vitro systems investigating superoxide production. We show that in addition to the well established production of superoxide from photosystem I, under reducing conditions superoxide is also produced by photosystem II, probably from the Q(A) site.

Benzoquinones↗
PubMed2002

Comparative environmental assessment of biocides used in antifouling paints.

In response to increasing scientific evidence on the toxicity and persistence of organotin residues from antifouling paints in the aquatic environment, the use of triorganotin antifouling products was banned on boats of less than 25 m length in many countries during 1987. Alternatives to tributyltin (TBT) paint are mainly copper based coatings containing organic booster biocides to improve the efficacy of the formulation, and have been utilised on small boats for the last 10 years. With policies encouraging a total ban on TBT, it is expected that these biocides will be used to a greater extent in the future. Limited data and information are available on the environmental occurrence, fate, toxicity, and persistence of these biocides, and thus any decisions on policies regulating antifoulants cannot be fully informed. In this study, a multicriteria comparison of alternative biocides, based on a general assessment of available information in the literature, provided support for the use of the precautionary principle with respect to policies on antifouling products. This assessment was validated by a more detailed comparison of four selected biocides and TBT. Results indicate that TCMS pyridine and TCMTB demonstrate environmental characteristics similar to TBT and thus detail risk assessments are needed before their use is permitted. The widespread use of the other biocides should be allowed only after research to fill the gaps in knowledge with respect to their toxicity and persistence in aquatic environments.

Aniline Compounds↗
PubMed1985

Translational regulation of protein synthesis, in response to light, at a critical stage of Volvox development.

In Volvox cultures synchronized by a light-dark cycle, juveniles containing presumptive somatic and reproductive cells are produced during the dark, but their cells do not differentiate until after the lights come on. The pattern of protein synthesis changes rapidly after the lights come on. Action spectra and effects of photosynthesis inhibitors indicate that this protein synthetic change is not simply a consequence of renewed flow of energy from illuminated chloroplasts. Actinomycin, at a level adequate to block the response to heat shock, has virtually no effect on the response of the same cells to light; furthermore, RNAs isolated from unilluminated and illuminated juveniles yield indistinguishable in vitro translation products. We conclude, therefore, that this effect of light is exerted almost exclusively at the translational level, generating one of the most striking examples of translational regulation yet described.

Animals↗
PubMed2000

Inhibition of denitrification by ultraviolet radiation.

It has been shown that UV-A (lambda=320-400 nm) and UV-B (lambda=280-320 nm) inhibit photosynthesis, nitrogen fixation and nitrification. The purpose of this study was to determine the effects, if any, on denitrification in a microbial community inhabiting the intertidal. The community studied is the microbial mat consisting primarily of Lyngbya that inhabits the Pacific marine intertidal, Baja California, Mexico. Rates of denitrification were determined using the acetylene blockage technique. Pseudomonas fluorescens (ATCC #17400) was used as a control organism, and treated similarly to the mat samples. Samples were incubated either beneath a PAR transparent, UV opaque screen (OP3), or a mylar screen to block UV-B, or a UV transparent screen (UVT) for 2 to 3 hours. Sets of samples were also treated with nitrapyrin to inhibit nitrification, or DCMU to inhibit photosynthesis and treated similarly. Denitrification rates were greater in the UV protected samples than in the UV exposed samples the mat samples as well as for the Ps fluorescens cultures. Killed controls exhibited no activity. In the DCMU and nitrapyrin treated samples denitrification rates were the same as in the untreated samples. These data indicate that denitrification is directly inhibited by UV radiation.

Ammonia↗
PubMed2004

Photobleaching of photosynthetic pigments in spinach thylakoid membranes. Effect of temperature, oxygen and DCMU.

The time dependence of photobleaching of photosynthetic pigments under high light illumination of isolated spinach thylakoid membranes at 22 and 4 degrees C was investigated. At 22 degrees C, the bleaching at 678, 472 and 436 nm was prominent but lowering the temperature up to 4 degrees C during illumination prevented the pigments from bleaching almost completely. The accelerating effect on pigment photobleaching by the presence of 3-(3,4 dichlorophenyl)-1,1-dimethyl-urea)-(DCMU), a well-known inhibitor of the electron transport and known to prevent photosystem I (PSI) and photosystem II (PSII) against photoinhibitory damage, was also suppressed at low temperature. At 22 degrees C in the presence and absence of DCMU, the decrease of the absorption at 678 and 472 nm was accompanied by a shift to the shorter wavelengths. To check the involvement of reactive oxygen species in the process, pigment photobleaching was followed in anaerobiosis. The effects of the three different environmental factors--light, temperature and DCMU--on the dynamics of photobleaching are discussed in terms of different susceptibility of the main pigment-protein complexes to photoinhibition.

Aerobiosis↗
PubMed2002

Characterization of a stress-responsive operon in the cyanobacterium Synechocystis sp. strain PCC 6803.

We previously identified a gene, slr0374, in the unicellular cyanobacterium, Synechocystis sp. strain PCC 6803, that was highly expressed under iron-deficient conditions [J. Bacteriol. 182 (2000) 3536]. The gene product contains an AAA domain, a putative leucine zipper and a phosphorylation site and is part of an operon (with slr0373 and slr0376) that is responsive to various environmental stresses. Primer extension mapping and transcript analysis in insertion mutants showed that all transcripts from this operon originated upstream of slr0373 at four contiguous transcription start sites before being processed into individual transcripts. Both primary and processed transcripts were quite stable. The start sites were sensitive to changes in sulfur, light and redox agent, as well as iron. The structural and regulatory elements of this operon were highly conserved in phycobilisome-containing cyanobacteria that have been sequenced to date. Slr0374 and Slr0376 show homology with Ycf46 and Ycf35, respectively.

Amino Acid Sequence↗