A simple new equation for the reversible temperature dependence of photosynthetic electron transport: a study on soybean leaf

2004 ◽  
Vol 31 (3) ◽  
pp. 275 ◽  
Author(s):  
Tania June ◽  
John R. Evans ◽  
Graham D. Farquhar
Keyword(s):  
Electron Transport ◽  
Temperature Dependence ◽  
Temperature Response ◽  
Photosynthetic Electron Transport ◽  
High Irradiance ◽  
Fluorescence Measurements ◽  
Glycine Max L ◽  
Soybean Leaf ◽  
New Equation ◽  
Soybean Leaves

The temperature response of Jmax, the irradiance-saturated potential rate of photosynthetic electron transport in the absence of Rubisco limitation, has usually been modelled by a complicated, modified Arrhenius type of equation. Light saturation can be difficult to achieve and reduces the precision of fluorescence measurements. Consequently, we calculated the rate of electron transport at 1200 μmol photosynthetically active radiation (PAR) quanta m–2 s–1 from chlorophyll fluorescence measurements on intact soybean leaves [Glycine max (L.) Merr] as temperature increased from 15 to 43°C with 1250 μmol mol–1 ambient [CO2]. Electron transport rate was maximal around 37°C and the decline in rate following further increases in leaf temperature to 43°C was found to be completely reversible immediately upon return to lower temperatures. We report a convenient, new equation for the temperature dependence of the rate of electron transport under high irradiance:...

Resistance to chlortoluron in a downy brome (Bromus tectorum) biotype

Weed Science ◽  
2006 ◽  
Vol 54 (02) ◽  
pp. 237-245 ◽  
Author(s):  
Julio Menendez ◽  
Fernando Bastida ◽  
Rafael de Prado
Keyword(s):  
Electron Transport ◽  
Photosynthetic Electron Transport ◽  
Fold Increase ◽  
Downy Brome ◽  
Fresh Weight ◽  
Wheat Field ◽  
P450 Monooxygenases ◽  
Fluorescence Measurements ◽  
Higher Ed ◽  
Herbicide Metabolism

A downy brome population in a winter wheat field at Córdoba, Spain, survived use rates of chlortoluron (2.5 to 3.5 kg ai ha−1) over 2 consecutive yr, where wheat monoculture and multiple annual chlortoluron applications had been carried out. The resistant (CR) biotype showed a higher ED50value (7.4 kg ai ha−1; the concentration required for 50% reduction of fresh weight) than the susceptible (S) control (2.2 kg ai ha−1), with a 3.4-fold increase in chlortoluron tolerance. Chlortoluron resistance in the CR downy brome biotype was not caused by altered absorption, translocation, or modification of the herbicide target site but by enhanced detoxification. The inhibition of both the recovery of photosynthetic electron transport and chlortoluron metabolism in the CR biotype due to the presence of the Cyt P450 inhibitor 1-aminobenzotriazole (ABT) indicates that herbicide metabolism catalyzed by Cyt P450 monooxygenases is related to chlortoluron resistance in CR plants. Although both biotypes degraded chlortoluron byN-dealkylation and ring-methyl hydroxylation and seem to share the same ability to form polar conjugates, degradation in the resistant biotype is more efficacious as this biotype metabolizes the parent herbicide faster and to a greater extent than its susceptible counterpart. The ability of the susceptible biotype to ring-hydroxylate chlortoluron, albeit at much slower rate, probably explains its moderate tolerance to chlortoluron observed in the growth assays and its minor photosynthetic electron transport recovery observed in fluorescence measurements.

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.

Superoxide-and Ethane-Formation in Subchloroplast Particles: Catalysis by Pyridinium Derivatives

1980 ◽  
Vol 35 (9-10) ◽  
pp. 770-775 ◽  
Author(s):  
E. F. Elstner ◽  
H. P. Fischer ◽  
W. Osswald ◽  
G. Kwiatkowski
Keyword(s):  
Electron Transport ◽  
Photosystem I ◽  
Photosynthetic Electron Transport ◽  
Redox Potentials ◽  
Light Reaction ◽  
Pyridinium Bromide ◽  
Superoxide Formation ◽  
Fatty Acid Peroxidation ◽  
Chlorophyll Bleaching ◽  
Ethane Formation

Abstract Oxygen reduction by chloroplast lamellae is catalyzed by low potential redox dyes with E′0 values between -0 .3 8 V and -0 .6 V. Compounds of E′0 values of -0 .6 7 V and lower are inactive. In subchloroplast particles with an active photosystem I but devoid of photosynthetic electron transport between the two photosystems, the active redox compounds enhance chlorophyll bleaching, superoxide formation and ethane production independent on exogenous substrates or electron donors. The activities of these compounds decrease with decreasing redox potential, with one exception: 1-methyl-4,4′-bipyridini urn bromide with an E′0 value of lower -1 V (and thus no electron acceptor of photosystem I in chloroplast lamellae with intact electron transport) stimulates light dependent superoxide formation and unsaturated fatty acid peroxidation in sub­ chloroplast particles, maximal rates appearing after almost complete chlorophyll bleaching. Since this activity is not visible with compounds with redox potentials below -0 .6 V lacking the nitrogen atom at the 1-position of the pyridinium substituent, we assume that 1 -methyl-4,4′-bi-pyridinium bromide is “activated” by a yet unknown light reaction.

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