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 703 records · Page 39Linked to original sources
PubMed1976

Stimulation of photosystem I-induced oxidation of chloroplast cytochrome b-559 by pre-illumination and by low pH.

(1) The proportion of higher plant chloroplast cytochrome b-559 oxidizable during illumination by low intensity 732 nm light increases as the pH is decreased below 6.5. At pH 5.0-5.3 total oxidation is seen and subsequent red light can cause reduction of up to 2/3 of the oxidized cytochrome. The oxidation by far red light at pH 5 is inhibited by 2 muM 2,5-dibromo-3-methyl-6-isopropyl-rho-benzoquinone whereas the red light-induced reduction is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. In this pH range ferricyanide-oxidized cytochrome b-559 exists in a form not reducible by ferrocyanide. (2) An increase in the amplitude of far-red induced oxidation also occurs at higher pH (up to pH 7.8) after pre-treatment of chloroplasts with substantially higher levels of light (approx. 10(6) ergs-cm-2-s-1). The degree of light activation is pH dependent, being more pronounced at lower pH. After light activation, cytochrome b-559 can be completely oxidized by far-red light in a manner reversible by red light up to pH values of 6, and the curve describing the amplitude of far-red oxidation as a function of pH is shifted by 0.5-1.0 pH unit toward higher pH. Far-red oxidation and red light reduction are again inhibited by 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone and 3-(3,4-dichlorophenyl)-1,1-dimethylurea, respectively. (3) Light activation at pH 5.2-6.0 is also manifested in a small decrease in the amplitude of subsequent dark ferrocyanide reduction, and this decrease is inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea (10 muM). (4) The effect of intramembranal acidity on the effective redox potential of cytochrome b-559 and its function is discussed.

Carbonyl Cyanide p-Trifluoromethoxyphenylhydrazone↗
PubMed1976

Evidence against proton gradient formation being the cause of chlorophyll fluorescence quenching by N-methylphenazonium methosulfate.

In strong illumination, 3-(3, 4-dichlorophenyl)-1,1-dimethylurea (DCMU)-poisoned chloroplasts exhibit a high yield of chlorophyll fluorescence while P-700 turnover, proton uptake, and phosphorylation are inhibited and a pH gradient is undectectable. When 10muM N-methylphenazonium methosulfate (PMS) is included, the fluorescence yield in light is substantially reduced, and when 100 muM ascorbate is also included, the yield is diminished approximately to the level in darkness. Only very slight increases in P-700 turnover and proton uptake (but no detectable pH gradient) accompany the fluorescence yield decline. When 10muM PMS and 15 mM ascorbate are added to poisoned chloroplasts (the oxygen concentration being greatly reduced), P-700 turnover, proton uptake, the pH gradient and phosphorylation all reach high levels. In this case, the yield of chlorophyll fluorescence is low and is the same in both light and dark. Further addition of an uncoupler eliminates proton uptake, the pH gradient and phosphorylation but does not significantly elevate the fluorescence yield. From these observations we suggest that, in DCMU-poisoned chloroplasts, the fluorescence quenching with PMS occurrs by a mechanism unrelated to the generation of a phosphyorylation potential. With chloroplasts unpoisoned by DCMU, PMS quenches fluorescence and considerably stimulates proton uptake, the pH gradient and phosphorylation. However, in this case, PMS serves to restore net electron transport.

Ammonia↗
PubMed1977

Slow fluorescence quenching of type A chloroplasts. Resolution into two components.

The divalent-cation-specific ionophore A23187 is used to define two components of the slow fluorescence quenching of type a spinach chloroplasts: ionophore-reversible and ionophore-resistant quenching. Ionophore-reversible quenching predominates at relatively low light intensities and approaches saturation as light levels are increased. It is sensitive to uncouplers and to 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and is dark reversible. At high light intensities the bulk (greater than 80%) of slow fluorescence quenching is ionophore-resistant. Ionophore-resistant quenching is stimulated by carbonyl cyanide m-chlorophenyl hydrazone (CCCP) at pH 7.6 and by both CCCP and methylamine at pH 9.0. It is insensitive to DCMU and is not reversed in subsequent darkness. Taken together, the two components account for all quenching observed in Type A chloroplasts. Ionophore-reversible quenching is identified with the Mg2+-mediated fluorescence quenching described by Krause (Biochim. Biophys. Acta (1974) 333, 301-313) and by Barber and Telfer (in Membrane Transport in Plants (Dainty, J., AND Zimmermann, U., eds.), pp. 281-288, Springer-Verlag, Berlin, 1974). Ionophore-resistant quenching, a first-order process requiring high light, resembles the quenching reported by Jennings et al. (Biochim. Biophys. Acta (1976) 423, 264-274). The resolution of the fluorescence quenching phenomenon into two distinct components reconciles the apparently contradictory observations of these earlier investigations.

Calcimycin↗
PubMed1977

515 nm Absorption changes in Chlorella at short times (4--100 mus) after a flash.

Using Chlorella, three types of absorption changes at 515 nm have been studied in the 4-100 mus time range following a flash. (1) The absorption change observed when both photoreactions are blocked, probably due to the formation of the triplet state of a carotenoid, is show to depend on Photosystem II excitation only. (2) The absorption increase induced by photoreaction I is biphasic; first phase, complete in less than 4 mus, followed by a slower phase with a half-rise time of 15-20 mus. (3) On the other hand, photoreaction II induces only a fast absorption increase (lessthan 4 mus). The time course of the biphasic 515 nm absorption increase induced by photoreaction I is similar to the biphasic absorption decrease previously observed at 480 nm by Cox and Delosme (1976, C.R. Acad. Sci. Paris 282D, 775-778). No significant absorption change is observed at 490 nm. These results suggest that the transmembrane electric field induced by photoreaction I rises to its maximum value in at least two phases within 100 mus following flash excitation.

Chlorella↗
PubMed1977

The photochemical and fluorescence properties of whole cells, spheroplasts and spheroplast particles from the blue-green alga Phormidium luridum.

The photochemical activities and fluorescence properties of cells, spheroplasts and spheroplast particles from the blue-green alga Phormidium luridum were compared. The photochemical activities were measured in a whole range of wavelengths and expressed as quantum yield spectra (quantum yield vs. wavelength). The following reactions were measured. Photosynthesis (O2 evolution) in whole cells; Hill reaction (O2 evolution) with Fe(CN)63- and NADP as electron acceptors (Photosystem II and photosystem II + Photosystem I reactions); electron transfer from reduced 2,6-dichlorophenolindophenol to diquat (Photosystem I reaction). The fluorescence properties were emission spectra, quantum yield spectra and the induction pattern. On the basis of comparison between the quantum yield spectra and the pigments compositions the relative contribution of each pigment to each photosystem was estimated. In normal cells and spheroplasts it was found that Photosystem I (Photosystem II) contains about 90% (10%) of the chlorophyll a, 90% (10%) of the carotenoids and 15% (85%) of the phycocyanin. In spheroplast particles there is a reorganization of the pigments; they loose a certain fraction (about half) of the phycocyanin but the remaining phycocyanin attaches itself exclusively to Photosystem I (!). This is reflected by the loss of Photosystem II activity, a flat quantum yield vs. wavelength dependence and a loss of the fluorescence induction. The fluorescence quantum yield spectra conform qualitatively to the above conclusion. More quantitative estimation shows that only a fraction (20--40%) of the chlorophyll of Photosystem II is fluorescent. Total emission spectrum and the ratio of variable to constant fluorescence are in agreement with this conclusion. The fluorescence emission spectrum shows characteristic differences between the constant and variable components. The variable fluorescence comes exclusively from chlorophyll a; the constant fluorescence is contributed, in addition to chlorophyll a, by phycocyanine and an unidentified long wavelength component. The variable fluorescence does not change in the transition from whole cells to spheroplasts. However, the constant fluorescence increases considerably. This indicates the release of a small fraction of pigments from the photosynthetic photochemical apparatus which then become fluorescent.

Cyanobacteria↗
PubMed1977

Estimation of chlorophyll a distribution in the photosynthetic pigment systems I and II of the blue-green alga Anabaena variabilis.

Chlorophyll a distribution in pigment systems I and II was estimated with the blue-green alga Anabaena variabilis by two methods: first, with intact cells using delayed light emission as an index reaction; second, by measuring the 2,6-dichlorophenolindophenol-Hill reaction and the cytochrome c photooxidation in membrane fragments. The first estimation indicated that 0.053+/-0.014 of total chlorophyll a functions as a component of pigment system II, and the second method 0.086+/-0.012. Though the values were somewhat different in the two methods, both estimations indicated that pigment system II chlorophyll a occupies a very small fraction of total chlorophyll a.

Chlorophyll↗
PubMed1977

Electron transport between plastoquinone and chlorophyll Ai in chloroplasts. II. Reaction kinetics and the function of plastocyanin in situ.

The light-induced reaction kinetics of electron carriers between the two light reactions were studied in spinach chloroplasts. 1. The difference spectrum of the absorbance changes of plastocyanin in situ was separated from superimposing absorbance changes by flash titration described in the preceding paper (Haehnel, W. (1973) Biochim. Biophys. Acta 305, 618-631). Relative amounts of 2 : 1 electron equivalents were observed for plastocyanin and chlorophyll a1 (P-700). 2. A balance of the electron equivalents released from reduced plastoquinone and simultaneously accepted by oxidized plastocyanin, cytochrome f and chlorophyll a1 indicated a quantitative electron transfer. Additional electron carriers between plastoquinone and light reaction I can be excluded with an accuracy of about +/-0.3 electron equivalents per light reaction II. 3. The time course of the absorbance changes of plastocyanin was measured at 584 nm with negligible interference with other absorbance changes. The reduction kinetics show an initial lag followed by a rise with a half time of about 20 ms. The redox states of plastocyanin and chlorophyll a1 during this reduction via the rate-limiting step between the light reactions and during oxidation by weak far-red light suggest a true equilibrium constant of about 20. 4. The simultaneous oxidation and reduction kinetics of plastoquinone, cytochrome f, plastocyanin and chlorophyll a1 induced by two successive groups of saturating flashes after far-red illumination were measured. The oxidation kinetics of plastocyanin and the simultaneous reduction kinetics of chlorophyll a1 after the single flashes indicate a quantitative electron transfer with a half time of 200 mus. 5. The fast reduction of chlorophyll a1 by plastocyanin showed no effect of the inhibitors 3-(3',4'-dichlorophenyl)-1,1-dimethylurea and 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone or of reduced phenazine methosulfate. But it was completed inhibited after KCN incubation. 6. The oxidation kinetics of cytochrome f were reinvestigated with high time resolution from the difference of absorbance changes at 554 minus 540 nm to minimize the disturbing interference with other absorbance changes. Absorbance changes measured 554 nm alone do not reflect kinetics of cytochrome f. The half time of the oxidation was faster than 40 microns. 7. The observed reaction kinetics gave evidence for a function of cytochrome f between plastoquinone and chlorophyll a1 in parallel to plastocyanin. In addition, they indicate that the greater portion of linear electron transport passes plastocyanin. The complex interaction between cytochrome f and chlorophyll a1 is discussed.

Chlorophyll↗
PubMed1977

Flash-induced 515 nm absorbance change in chloroplasts with various granum contents.

The 515 nm absorbance change was studied in mesophyll and bundle sheath chloroplasts of maize, which contain different amounts of grana. The amplitude of the 515 nm signal (induced by 3 micro seconds flashes repeated at 4 s intervals) has shown a correlation with the granum content of the samples. However, upon addition of N-methylphenazonium methosulphate the 515 nm signal became independent of the amount of grana: in agranal thylakoids a large pool of silent Photosystem I was activated and, as a result, the amplitude of the 515 nm signal of agranal chloroplasts increased to the level exhibited by granal chloroplasts. These data show that the 515 nm absorbance change is not limited to small closed vesicles like grana, but in the presence of suitable electron donors single lamellae of bundle sheath chloroplasts can also be active.

Chloroplasts↗
PubMed1977

Identification of S2 as the sensitive state to alkaline photoinactivation of photosystem II in chloroplasts.

1. Chloroplasts have been preilluminated by a sequence of n short saturating flashes immediately before alkalinization to pH 9.3, and brought back 2 min later to pH 7.8. The assay of Photosystem II activity through dichlorophenolindophenol photoreduction, oxygen evolution, fluorescence induction, shows that part of the centers is inactivated and that this part depends on the number of preilluminating flashes (maximum inhibition after one flash) in a way which suggests identification of state S2 as the target for alkaline inactivation. 2. As shown by Reimer and Trebst ((1975) Biochem. Physiol. Pflanz. 168, 225-232) the inactivation necessitates the presence of gramicidin, which shows that the sensitive site is on the internal side of the thylakoid membrane. 3. The electron flow through inactivated Photosystem II is restored by artificial donor addition (diphenylcarbazide or hydroxylamine); this suggests that the water-splitting enzyme itself is blocked. The inactivation is accompanied by a solubilization of bound Mn2+ and by the occurence of EPR Signal II "fast". 4. Glutaraldehyde fixation before the treatment does not prevent the inactivation which thus does not seem to involve a protein structural change.

2,6-Dichloroindophenol↗
PubMed1977

Kinetics of chlorophyll fluorescence at 77K in Chlorella and chloroplasts. Effects of CCCP, ferricyanide and DCMU.

The kinetics of chlorophyll fluorescence at 77K were studied in Chlorella cells and spinach chloroplasts. During a first illumination, the rise is polyphasic with at least three phases. The slowest one is irreversible and corresponds to the cytochrome oxidation. The dark regeneration of half the variable fluorescence is biphasic, the fast phase being inhibited by 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) both in Chlorella and chloroplasts. The fluorescence rise during a second illumination is still biphasic. Carbonyl cyanide m-chlorophenylhydrazone (CCCP) slows down the fluorescence rise in Chlorella but has no effect on the dark regeneration. It does not affect the fluorescence of chloroplasts. Ferricyanide which oxidizes cytochrome beta-559 at room temperature produces a quenching of the variable fluorescence and an acceleration of the fluorescence rise during the first illumination. Our results fit the idea of the heterogeneity of the Photosystem II centers at low temperature.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1977

The binding of bicarbonate ions to washed chloroplast grana.

Radioactive labelling techniques show that isolated broken chloroplasts can take up HCO3-in the dark. There are two pools of binding sites for this ion on, or within, the thylakoid membranes. A smaller, high affinity pool exists at a concentration of one HCO3-bound per 380-400 chlorophyll molecules. Removal of HCO3-bound in this pool requires special conditions and results in greater than 90% inhibition of oxygen evolution. The inhibition is fully reversed when HCO3-is added back. HCO3-bound in the small pool does not necessarily exchange with free HCO3-in the dark or in light. Evidence presented suggests that this site is very near the site of action of 3-(3,4-dichlorophenyl)-1,1-dimethyl urea. A second, much larger, pool of HCO3-binding sites also exists in a concentration approaching that of the bulk chlorophyll. These sites have a much lower affinity for HCO3-, and their function has not yet been determined.

Bicarbonates↗
PubMed1977

Characterization of the low temperature thermoluminescence band Zv in leaf: an explanation for its variable nature.

Out of the six thermoluminescence bands reported for a mature leaf, one band (Zv) appearing at the lowest temperatures is dependent on the temperature of illumination. The characteristics of this band in fresh leaf are compared with those is a leaf heated to 60 degrees C for 5 min. It is concluded here that this band, following illumination at temperatures lower than 173 K, is part of Arnold and Azzi's Z band (Arnold, W. and Azzi, J.R. (1971) Photochem. Photobiol. 14, 233--240). However, it is part of peak I when observed subsequent to illumination beyond 173 K. An explanation for the appearance of this band at different temperatures is proposed.

Cold Temperature↗
PubMed1977

The light dependent uptake of N-methylphenazinium cations by the thylakoids of isolated chloroplasts.

The absorption of N-methylphenazinium methylsulfate (MP+ methylsulfate) in suspensions of envelope-free chloroplasts is reversibly lowered in the light. When the electron transport system of the chloroplasts is inhibited by 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU), the photobleaching reflects an uptake of MP+ into the thylakoids. Its magnitude is a function of the composition and of the pH of the suspension medium and, most importantly, is controlled by the availability of permeant anions which apparently accompany MP+ into the thylakoid as counterions. Consequently, the rate of the bleaching is strongly dependent on the permeability of the thylakoid to the available anion. At pH 7.5, the thylakoids of DCMU poisoned pokeweed chloroplasts are able to hold at least 6 MP+/chlorophyll. It is proposed that, in the presence of MP+, the light reaction of Photosystem I in DCMU-inhibited chloroplasts causes a conformational change of the membranes which exposes nucleophilic sites inside the thylakoids. These sites appear to have a high affinity for MP+, but may bind protons or other cations under certain experimental conditions. The uptake of MP+ has a hypochromic effect on its absorption band in the near ultraviolet due to the resulting heterogeneous distribution of the dye cation between medium and chloroplast grana.

Biological Transport↗
PubMed1977

Photooxidation of chlorophyll in spinach chloroplasts between 10 and 180 K.

Electron paramagnetic resonance (EPR) and optical absorbance difference spectra and kinetics upon illumination by saturating flashes and continuous light of spinach chloroplasts frozen under various conditions were measured between 10 and 180 K. 1. At 100 K illumination with continuous light caused an EPR signal which decayed during the light in about 30 ms. This change is probably due to the reduction of P+-680, the oxidized primary electron donor of Photosystem II, by a secondary electron donor, cytochrome b-559. Flash illumination yielded the previously observed rapid (2 ms) transient. This transient has been ascribed to a back-reaction of the two primary reagents of Photosystem II (Malkin, R. and Bearden, A.J. (1975) Biochim. Biophys. Acta 396, 250-259; Visser, J.W.M. (1975) Thesis, Leiden). 2. Between 10 and 40 K, illumination with continuous light showed a transient which decayed in about 500 ms. The extent decreased with increasing temperature. However, the half time appeared to be temperature independent. This signal was also attributed to P+-680. 3. At 180 K it appeared to be impossible to observe the 2 and 30 ms components in dark frozen chloroplasts. However, they could be observed again if two short saturating flashes were given shortly before freezing. These changes seem to be dependent on the S-state of the reaction center. 4. After oxidizing the sample with ferricyanide (Eh = 540 mV), the light induced absorbance difference spectrum showed a bleaching near 676 nm. This change is ascribed to the irreversible oxidation of a dimeric chlorophyll molecule which acts as electron donor to P+-680 under these conditions. 5. Titration curves of the irreversible light-induced absorbance change at 676 nm and the irreversible light-induced EPR change near g = 2.00 provide strong evidence that these two changes reflect the same compound. Finally, a model is given to explain the observed reactions of Photosystem II at 10-180 K. The model involves three different ultimate and one intermediate electron donor to P+-680 at these temperatures.

Chlorophyll↗
PubMed1977

Oxidation-reduction coupled phosphorylation in the dark with isolated spinach chloroplasts.

1. Spinach chloroplasts, pre-incubated with ferricyanide, acquire the ability to make ATP in the dark provided they are supplied with a reductant and a lipophilic mediator that can penetrate the membrane. The mediator must be of the type that, upon oxidation, releases protons into the surrounding medium such as 2,3,5,6-tetramethyl-p-phenylenediamine (DAD). 2. Dark phosphorylation is not affected by the electron transport inhibitor, 3(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) or 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB), but is inhibited by uncouplers of photophosphorylation (e.g. NH4Cl and carbonylcyanide-m-chlorophenylhydrazone (CCCP)) and high concentrations of the energy transfer inhibitor, Dio-9. 3. Because only catalytic amounts of the mediator DAD are required to saturate dark phosphorylation, it is concluded that DAD shuttles reducing equivalents across the membrane from the reductant, ascorbate, on the outside to ferricyanide, the oxidant, trapped on the inside. 4. The results are interpreted within the framework of the chemiosmotic hypothesis for the coupling of electron transport to phosphorylation.

Adenosine Triphosphate↗
PubMed1977

Relationship between inhibitor binding by chloroplasts and inhibition of photosynthetic electron transport.

The binding of radioactively labelled atrazin, metribuzin and phenmedipham by broken chloroplasts was studied. From the double-reciprocal plots (bound vs. free inhibitors) a high affinity binding reaction is graphically isolated which is related to the inhibition of photosynthetic electron transport. It is concluded that the specific binding sites correspond to the electron carrier molecules which are attacked by the inhibitors. The relative concentration of specific binding sites is 1 per 300-500 chlorophyll molecules. The binding of the labelled substances is competitively inhibited by each of the indicated unlabelled substances, by DCMU and by several pyridazinone derivatives. These results suggest that triazines, triazinones, pyridazinones, biscarbamates and phenylureas interfere with the same electron carrier of the photosynthetic electron transport chain, according to the same molecular mechanism.

Atrazine↗
PubMed1977

Flash induced fluorescence kinetics in chloroplasts in the 20 microseconds-100 s time range in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea. Effects of hydroxylamine.

Flash induced variations of the fluorescence yield have been studied at 2 degrees C over a long time range (at 1 microseconds and from 20 microseconds to 3 min) in chloroplasts in the presence of 3(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) with or without addition of hydroxylamine. 1. In the presence of DCMU, a polyphasic rise is observed. A first fast rise (less than 1 microseconds) is ascribed to the transfer of the positive charge from the primary Photosystem II donor Chl to a secondary donor Y. Two hypotheses are proposed to interpret the existence of the subsequent slower increase (t1/2 approximately equal to 70 microseconds) which then follows the initial fast rise. 2. The effects or various hydroxylamine concentrations have been studied with a sufficient incubation time to inactivate the secondary donors Y and Z. This inactivation leads to a complete inhibition of the ability to emit oxygen. Under these conditions, the initial fast rise (less than 1 microseconds) is inhibited as shown by den Haan, G.A., Duysens, L. N. M. and Egberts, D. J. N. (1974) Biochim. Biophs. Acta 368, 409-421, and the oxidized Chl+ is reduced by an auxiliary donor D. The slow fluorescence rise observed after destruction of Y and Z has a similar kinetic behaviour to that observed in the presence of DCMU only and is polyphasic. In the presence of 10 mM hydroxylamine, the constant rate of the back reaction k1 between Chl+ and the primary acceptor Q- is estimated to be approx. (135 microseconds)-1 while the transfer of the positive charge from Chl+ to D has a rate constant k2 of approx. (105 microseconds)-1. 3. In the presence of hydroxylamine concentrations higher than 10 mM, there appears a rise in the 1-20 microseconds range ascribed to a direct reduction of oxidized Chl+ by hydroxylamine. 4. In chloroplasts treated with 10 mM hydroxylamine for 15 min and washed afterwards, the rate constant k3 of the back reaction between D+ and Q- is estimated to be approx. (100 ms)-1 which leads to a value of about 700 for the equilibrium constant between Chl and D. Hydroxylamine added under these conditions is able to reduce D+. The rate constant k4 of this reduction is estimated to be (350 ms)-1 in 0.1 mM hydroxylamine.

Chlorophyll↗