Photosynthetic Electron Transport Inhibitors: Some Problems Related to an Accurate Determination of the Molecular Site of Action

1984 ◽  
Vol 39 (5) ◽  
pp. 338-341 ◽  
Author(s):  
C. J. van Assche
Keyword(s):  
Accurate Determination ◽  
Photosynthetic Electron Transport ◽  
Threshold Value ◽  
Fluorescence Induction ◽  
Back Reaction ◽  
Ps Ii ◽  
Chlorophyll Fluorescence Parameters ◽  
Transport Inhibitors ◽  
Kinetics Of

When DCMU and DCMU-type inhibitor concentrations vary over a large range, different effects may be observed on chlorophyll fluorescence parameters such as fluorescence transients, areas over fluorescence induction curves as well as kinetics of area accumulation. These results would indicate a heterogeneity of PS II electron acceptors, or an inhibitor partitioning behavior dependent on the concentration. Also, a threshold value can be reached at supra-optimal concentrations, beyond which the back reaction is almost completely blocked. Such an approach makes it possible to find out inconsistencies in the results, brought about by dual effects of some inhibitors such as phenol-type herbicides, as previously proposed.

scholarly journals Photosystem II: Thermodynamics and Kinetics of Electron Transport from QA- to QB(QB- ) and Deleterious Effects of Copper(II)

1993 ◽  
Vol 48 (3-4) ◽  
pp. 234-240 ◽  
Author(s):  
G. Renger ◽  
H. M. Gleiter ◽  
E. Haag ◽  
F. Reifarth
Keyword(s):  
Oxygen Evolution ◽  
Manganese Content ◽  
Fluorescence Emission ◽  
Laser Flash ◽  
Fluorescence Induction ◽  
Oxygen Evolving Complex ◽  
Ps Ii ◽  
Thermodynamics And Kinetics ◽  
Redox Active ◽  
Kinetics Of

Studies on thermodynamics and kinetics of electron transfer from QA- to QB(QB-) were performed by monitoring laser flash induced changes of the relative fluorescence emission as a function of temperature (220 K < T < 310 K) in isolated thylakoids and PS II membrane fragments.In addition, effects of bivalent metal ions on PS II were investigated by measuring conventional fluorescence induction curves, oxygen evolution, manganese content and atrazine binding mostly in PS II membrane fragments. It was found: a) the normalized level of the fluorescence remaining 10 s after the actinic flash (Ft/F0) steeply increases at temperatures below -10 to - 20 °C, b) the fast phase of the transient fluorescence change becomes markedly retarded with decreasing temperatures, c) among different cations (Cu2+, Zn2+, Cd2+, Ni2+, Co2+) only Cu2+ exhibits marked effects in the concentration range below 100 μᴍ and d) Cu2+ decreases the normalized variable fluorescence, inhibits oxygen evolution and diminishes the affinity to atrazine binding without affecting the number of binding sites. The content of about four manganeses per functionally competent oxygen evolving complex is not changed by [Cu2+] < 70 μᴍ.Based on these findings it is concluded: i) a temperature dependent equilibrium between an inactive (I) and active (A) state of QA- reoxidation by QB(QB- ) is characterized by standard enthalpies ΔH° of 95 kJ mol-1 and 60 kJ mol-1 and standard entropies ΔS° of 370 kJ K-1 mol-1 and 240 kJ K-1 mol-1 in isolated thylakoids and PS II membrane fragments, respectively, ii) the activation energies of QA- reoxidation by plastoquinone bound to the QB site are about 30 kJ mol-1 (thylakoids) and 40 kJ mol-1 (PS II membrane fragments) in 220 K < T < 300 K, and iii) Cu2+ causes at least a two-fold effect on PS II by modifying the atrazine binding affinity at lower concentrations ( ~ 5 μᴍ) and interference with the redox active tyrosine Yz at slightly higher concentration ( ~ 10 μᴍ) leading to blockage of oxygen evolution.

Reactive Diffusion upon Planar Dissolving Copper in Solder Melts

2011 ◽  
Vol 309-310 ◽  
pp. 127-134 ◽  
Author(s):  
Jaromír Drápala ◽  
Pavel Jopek ◽  
Daniel Petlák ◽  
Petr Harcuba ◽  
Petr Kubíček
Keyword(s):  
Interphase Boundary ◽  
Time Course ◽  
Solid Phase ◽  
Accurate Determination ◽  
Theoretical Description ◽  
Reactive Diffusion ◽  
Boundary Movement ◽  
Original Metal ◽  
Kinetics Of

Problems of reactive diffusion at a solid phase - melt contact were studied theoretically. The main intention was to calculate the time course of the solid phase dissolving in the case of planar dissolving. In our work we give heed especially to the dominating process, which is the solid metal A dissolving in solder melt B. During the dissolving, melt B saturates with metal A, and the process is influenced by convections which are characteristic for a given experimental configuration. A theoretical description of the kinetics of solid phase dissolving in the melt will be presented for the case of planar dissolving. The aim is to derive a relation for the interphase boundary movement (t) depending on time and a time course of growth of the element A concentration in the melt B. There are difficulties in accurate determination of the interphase boundary movement after heating of specimens for certain time intervals. It should be performed experimentally, since intermetallic phases are formed in original metal A both via diffusion and upon cooling and some phases segregate upon cooling of the solidifying melt. The main intention was to study experimentally the copper dissolving in melts of various solder alloys and the related reactive diffusion. We used pure Sn and Sn-Cu, Sn-Ag-Cu, Sn-Sb, Sn-Zn alloys as solder materials. Experiments aimed at the study of a Cu plate dissolving in the solder melt were carried out at various selected temperatures and times. The problems of reactive diffusion were studied both theoretically and experimentally and the problems that have to be solved preferably were emphasized. Concentration profiles of elements and thickness of layers of phases can be determined with SEM and X-ray microanalyses (WDX, EDX) of specimens after their diffusion heating.

Rapid and accurate prediction of the frequencies of Bursaphelenchus xylophilus and B. mucronatus in mixed nematode samples using real-time species-specific PCR

Nematology ◽  
2009 ◽  
Vol 11 (2) ◽  
pp. 289-299 ◽  
Author(s):  
Si Hyeock Lee ◽  
Il Sung Moon ◽  
Jae Soon Kang ◽  
Sang Chul Shin ◽  
Sang Gil Lee
Keyword(s):  
Real Time ◽  
Detection System ◽  
Accurate Determination ◽  
Marker Gene ◽  
Threshold Value ◽  
Nematode Species ◽  
Bursaphelenchus Xylophilus ◽  
Specific Pcr ◽  
Species Specific

AbstractAccurate detection of Bursaphelenchus xylophilus and prediction of its frequency in crude nematode samples is often hindered by the coexistence of related nematode species, such as B. mucronatus, that are morphologically similar but non-pathogenic. To establish a detection system enabling determination of the relative frequencies of B. xylophilus and B. mucronatus from field nematode samples, we developed a real-time species-specific PCR (rtssPCR) protocol which targets the substantial sequence differences in the 5S rRNA marker gene between the two nematode species. Using standard DNA mixtures of B. xylophilus and B. mucronatus in various ratios, plots of percent species proportion vs cycle threshold value (Ct value) were generated for the prediction of species frequency. The rtssPCR protocol enables the detection of target nematode frequencies as low as 0.16% at the 95% confidence level. When nematode DNA samples were extracted from the mixed specimens of B. xylophilus and B. mucronatus in various ratios and analysed by rtssPCR, the semi-log plot was nearly identical to the plot generated from standard mixed DNA samples, demonstrating that field populations of the nematodes can be directly used for rtssPCR analysis. The rapid and accurate determination of B. xylophilus or B. mucronatus frequencies by this rtssPCR protocol makes it ideal for routine monitoring and quarantine of B. xylophilus in the field.

scholarly journals An automated flow platform for accurate determination of gas–liquid–solid reaction kinetics

2020 ◽  
Vol 5 (9) ◽  
pp. 1751-1758
Author(s):  
Xiaonan Duan ◽  
Jiacheng Tu ◽  
Andrew R. Teixeira ◽  
Le Sang ◽  
Klavs F. Jensen ◽  
...  
Keyword(s):  
Reaction Kinetics ◽  
Accurate Determination ◽  
Packed Bed ◽  
Packed Bed Reactor ◽  
Solid Reaction ◽  
Hydrogenation Reactions ◽  
Kinetics Of

An automated flow platform based on a tube-in-tube contactor and micro-packed bed reactor is developed to measure the kinetics of gas–liquid–solid hydrogenation reactions.

Determination of Herbicide Inhibition of Photosynthetic Electron Transport by Fluorescence

Weed Science ◽  
1983 ◽  
Vol 31 (3) ◽  
pp. 361-367 ◽  
Author(s):  
Edward P. Richard ◽  
John R. Goss ◽  
Charles J. Arntzen ◽  
Fred W. Slife
Keyword(s):  
Electron Transport ◽  
Foliar Application ◽  
Photosynthetic Electron Transport ◽  
Fluorescence Measurements ◽  
Abaxial Leaf Surface ◽  
Terminal Level ◽  
Non Destructive ◽  
Kinetics Of ◽  
Chl Fluorescence

The kinetics of chlorophyll (Chl) fluorescence was used as a tool for detecting herbicide inhibition in studies using intact soybean [Glycine max(L.) Merr.] leaves. The terminal level of fluorescence (FT), obtained 150 s after the onset of illumination of the abaxial leaf surface, was found to be independent of the dark preadaptation interval and to vary little between leaflets and leaves within and among untreated plants. Increases in FTwere detected in plants following the foliar application of herbicides which inhibit photosynthetic electron transport. Fluorescence measurements indicated significant electron transport inhibition in leaves following treatment with 40-mM solutions of either atrazine [2-chloro-4-(ethylamino)-6-(isopropyiamino)-s-triazine] or diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] after 0.5 and 1 h, respectively. Results of this study indicate that Chl fluorescence can be used to measure injury qualitatively by photosynthetic electron transport-inhibiting herbicides in intact plants long before visual symptoms of injury occur. Possible uses of this sensitive, rapid, and non-destructive technique for studying herbicide penetration as affected by adjuvants and environmental factors are discussed.

Kinetic Evaluation of Carbon Formation in Steam/CO2-Natural Gas Reformers. Influence of the Catalyst Activity and Alkalinity

2002 ◽  
Vol 1 (1) ◽  
Author(s):  
Joost-Willem Snoeck ◽  
Gilbert Froment ◽  
Martin Fowles
Keyword(s):  
Natural Gas ◽  
Gas Phase ◽  
Catalyst Activity ◽  
Accurate Determination ◽  
Activity Level ◽  
Carbon Formation ◽  
Kinetic Evaluation ◽  
Detailed Kinetics ◽  
Kinetics Of

The production of synthesis gas with a low H2/CO ratio from natural gas requires recycling the produced CO2, but this enhances the risk of carbon formation. A simulation model for steam/CO2 reformers comprising detailed kinetics of the main reactions but also of the carbon formation and gasification was used to evaluate the potential of carbon formation in the bulk gas phase and inside the catalyst particles along the reactor tube. Simulation results are presented for a number of cases with varying amounts of CO2 in the feed. The model permits an accurate determination of the minimum amount of steam or the maximum amount of CO2 that can be tolerated in the feed. Thermodynamic and kinetic criteria are compared, and a strategy for the evaluation of the risk of carbon formation is proposed. The importance of the activity level of the catalyst and of its alkalinity is also illustrated.

scholarly journals Effects of Heavy Metals on the Fast Chlorophyll Fluorescence Induction Kinetics of Photosystem II: a Comparative Study

1999 ◽  
Vol 54 (9-10) ◽  
pp. 735-739 ◽  
Author(s):  
M. Ciscato ◽  
J. Vangronsveld ◽  
R. Valcke
Keyword(s):  
Time Course ◽  
Fluorescence Induction ◽  
Chlorophyll Fluorescence Induction ◽  
Ps Ii ◽  
Induction Kinetics ◽  
Fluorescence Induction Kinetics ◽  
Bean Plants ◽  
Chlorophyll Fluorescence Induction Kinetics ◽  
Toxic Concentrations ◽  
Kinetics Of

The effects of toxic concentrations of Cu, Zn and Cd on the fast induction kinetics of fluorescence from photosystem(PS)II were investigated in a comparative way. The fast fluorescence transient from primary leaves of metal-treated bean plants was studied. During several days after metal application, the time course of the changes induced by the different metals was monitored. The results evidenced not only a different time course of the changes in fluorescence related parameters for the three metals, but also different effects on the fluorescence induction kinetics, which could possibly be linked to different mechanisms of action of the metals

Fluorometric Detection of Photosystem II Herbicide Penetration and Detoxification in Whole Leaves

Weed Science ◽  
1984 ◽  
Vol 32 (5) ◽  
pp. 675-680 ◽  
Author(s):  
Manfred Voss ◽  
Gernot Renger ◽  
Clemens Kötter ◽  
Peter Gräber
Keyword(s):  
Photosystem Ii ◽  
Foliar Application ◽  
Fluorescence Induction ◽  
Fluorometric Detection ◽  
Variable Fluorescence ◽  
Ps Ii ◽  
Fluorescence Measurements ◽  
Detoxification Mechanism ◽  
Herbicide Effects ◽  
Kinetics Of

The applicability of fluorescence measurements for the detection of herbicide effects in whole leaves was analyzed. Based on the results known for isolated chloroplasts, normalized variable fluorescence of the initial rise was shown to be an appropriate tool for monitoring effects of photosystem II (PS II) herbicides. Equipment is described for monitoring the degree of inhibition by fluorescence induction measurements and microcomputer data analysis. The method is used to study the effect of pyrazon [5-amino-4-chloro-2-phenyl-3(2H)-pyridazinone], BAY DRW 1139 [4-amino-3-methyl-6-phenyl-1,2,4-triazin-5(4H)-one], and phenmedipham {3-[(methoxycarbonyl)amino] phenyl (3-methyl-phenyl)carbamate} after foliar application to different species. A rapid decrease of normalized variable fluorescence indicates penetration into leaf cells of all species tested. During a 5- to 7-day experiment, the apparent variable fluorescence decreased continuously in herbicide-susceptible plants, while it recovered in resistant plants due to an internal detoxification mechanism. The described method provides a rapid, simple, and nondestructive tool for analyzing the kinetics of penetration and detoxification of PS II herbicides in whole leaves.

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