The drug ornidazole inhibits photosynthesis in a different mechanism described for protozoa and anaerobic bacteria

2016 ◽  
Vol 473 (23) ◽  
pp. 4413-4426 ◽  
Author(s):  
Yehouda Marcus ◽  
Noam Tal ◽  
Mordechai Ronen ◽  
Raanan Carmieli ◽  
Michael Gurevitz
Keyword(s):  
Electron Transport ◽  
Nitro Group ◽  
Bacterial Infections ◽  
Electron Tunneling ◽  
Anaerobic Bacteria ◽  
Calvin Cycle ◽  
Photosynthetic Electron Transport ◽  
Iron Sulfur Cluster ◽  
Efficient Inhibitor ◽  
Oxygen Photoreduction

Ornidazole of the 5-nitroimidazole drug family is used to treat protozoan and anaerobic bacterial infections via a mechanism that involves preactivation by reduction of the nitro group, and production of toxic derivatives and radicals. Metronidazole, another drug family member, has been suggested to affect photosynthesis by draining electrons from the electron carrier ferredoxin, thus inhibiting NADP+ reduction and stimulating radical and peroxide production. Here we show, however, that ornidazole inhibits photosynthesis via a different mechanism. While having a minute effect on the photosynthetic electron transport and oxygen photoreduction, ornidazole hinders the activity of two Calvin cycle enzymes, triose-phosphate isomerase (TPI) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Modeling of ornidazole's interaction with ferredoxin of the protozoan Trichomonas suggests efficient electron tunneling from the iron–sulfur cluster to the nitro group of the drug. A similar docking site of ornidazole at the plant-type ferredoxin does not exist, and the best simulated alternative does not support such efficient tunneling. Notably, TPI was inhibited by ornidazole in the dark or when electron transport was blocked by dichloromethyl diphenylurea, indicating that this inhibition was unrelated to the electron transport machinery. Although TPI and GAPDH isoenzymes are involved in glycolysis and gluconeogenesis, ornidazole's effect on respiration of photoautotrophs is moderate, thus raising its value as an efficient inhibitor of photosynthesis. The scarcity of Calvin cycle inhibitors capable of penetrating cell membranes emphasizes on the value of ornidazole for studying the regulation of this cycle.

scholarly journals Effects of red and blue light on leaf anatomy, CO2 assimilation, and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

2020 ◽  
Author(s):  
Yan Li ◽  
Guofeng Xin ◽  
Chang Liu ◽  
Qinghua Shi ◽  
Fengjuan Yang ◽  
...  
Keyword(s):  
Electron Transport ◽  
Capsicum Annuum ◽  
Leaf Anatomy ◽  
Calvin Cycle ◽  
Biomass Accumulation ◽  
Photosynthetic Electron Transport ◽  
Sweet Pepper ◽  
Transport Capacity ◽  
Ribulose 1 ◽  
Electron Transportation

Abstract Background: The red (R) and blue (B) light wavelengths are known to influence many plant physiological processes during growth and development, particularly photosynthesis. To understand how R and B light influences plant photomorphogenesis and photosynthesis, we investigated changes in leaf anatomy and stomatal traits, chlorophyll fluorescence and photosynthetic parameters, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and Calvin cycle-related enzymes expression and their activities in sweet pepper (Capsicum annuum L.) seedlings exposed to four light qualities: monochromatic white (W, control), R, B, and mixed R and B (RB) light with the same photosynthetic photon flux density (PPFD) of 300 μmol/m2·s. Results: The results revealed that seedlings grown under R light had lower biomass accumulation, CO2 assimilation, and photosystem II (PSII) electron transportation compared to plants grown under the other treatments. These changes are probably due to inactivation of the photosystem (PS). Biomass accumulation and CO2 assimilation were significantly enriched in B- and RB-grown plants, especially the latter treatment. Their leaves were also thicker, and stomatal conductance, photosynthetic electron transport capacity, and the photosynthetic rate were enhanced. The up-regulation of the expression and activities of Rubisco, fructose-1, 6-bisphosphatase (FBPase), and fructose-1, 6-bisphosphate aldolase (FBA), which are involved in the Calvin cycle and are probably the main enzymatic factors contributing to RuBP (ribulose-1, 5-bisphosphate) synthesis, also increased. Conclusions: Mixed R and B light altered plant photomorphogenesis and photosynthesis, mainly through its effects on leaf anatomy, photosynthetic electron transportation, and the expression and activities of key Calvin cycle enzymes.

scholarly journals Effects of red and blue light on leaf anatomy, CO2 assimilation, and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

2020 ◽  
Author(s):  
Yan Li ◽  
Guofeng Xin ◽  
Chang Liu ◽  
Qinghua Shi ◽  
Fengjuan Yang ◽  
...  
Keyword(s):  
Electron Transport ◽  
Capsicum Annuum ◽  
Leaf Anatomy ◽  
Calvin Cycle ◽  
Biomass Accumulation ◽  
Photosynthetic Electron Transport ◽  
Sweet Pepper ◽  
Transport Capacity ◽  
Ribulose 1 ◽  
Electron Transportation

Abstract Background: The red (R) and blue (B) light wavelengths are known to influence many plant physiological processes during growth and development, particularly photosynthesis. To understand how R and B light influences plant photomorphogenesis and photosynthesis, we investigated changes in leaf anatomy, chlorophyll fluorescence and photosynthetic parameters, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and Calvin cycle-related enzymes expression and their activities in sweet pepper (Capsicum annuum L.) seedlings exposed to four light qualities: monochromatic white (W, control), R, B and mixed R and B (RB) light with the same photosynthetic photon flux density (PPFD) of 300 μmol/m2·s. Results: The results revealed that seedlings grown under R light had lower biomass accumulation, CO2 assimilation and photosystem II (PSII) electron transportation compared to plants grown under other treatments. These changes are probably due to inactivation of the photosystem (PS). Biomass accumulation and CO2 assimilation were significantly enriched in B- and RB-grown plants, especially the latter treatment. Their leaves were also thicker, and photosynthetic electron transport capacity, as well as the photosynthetic rate were enhanced. The up-regulation of the expression and activities of Rubisco, fructose-1, 6-bisphosphatase (FBPase) and glyceraldehyde-phosphate dehydrogenase (GAPDH), which involved in the Calvin cycle and are probably the main enzymatic factors contributing to RuBP (ribulose-1, 5-bisphosphate) synthesis, were also increased. Conclusions: Mixed R and B light altered plant photomorphogenesis and photosynthesis, mainly through its effects on leaf anatomy, photosynthetic electron transportation and the expression and activities of key Calvin cycle enzymes.

Inhibition of Photosynthetic Electron Transport by the Quinone Antagonist UHDBT

1981 ◽  
Vol 36 (3-4) ◽  
pp. 272-275 ◽  
Author(s):  
Walter Oettmeier ◽  
Klaus Masson ◽  
Doris Godde
Keyword(s):  
Electron Transport ◽  
Green Alga ◽  
Photosynthetic Electron Transport ◽  
Binding Studies ◽  
Chlamydomonas Reinhardii ◽  
Efficient Inhibitor ◽  
Low Concentrations

UHDBT (5-n-undecyl-6-hydroxy-4,7-dioxobenzothiazole) is an efficient inhibitor of photosynthetic electron transport in chloroplasts from spinach (pI50-value = 7.61) and the green alga Chlamydomonas reinhardii. At low concentrations of UHDBT its site of inhibition is located at the reducing side of plastoquinone, identical to that of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU). This became evident from functional as well as binding studies. At higher concentrations of UHDBT a secondary inhibition site at the oxidizing side of plastoquinone, identical to that of 2,5-dibromo-3-methyl-6-isopropyl-1,4-benzoquinone (DBMIB) becomes evident

scholarly journals Effects of red and blue light on leaf anatomy, CO2 assimilation, and the photosynthetic electron transport capacity of sweet pepper (Capsicum annuum L.) seedlings

2020 ◽  
Author(s):  
Yan Li ◽  
Guofeng Xin ◽  
Chang Liu ◽  
Qinghua Shi ◽  
Fengjuan Yang ◽  
...  
Keyword(s):  
Electron Transport ◽  
Capsicum Annuum ◽  
Leaf Anatomy ◽  
Calvin Cycle ◽  
Biomass Accumulation ◽  
Photosynthetic Electron Transport ◽  
Sweet Pepper ◽  
Transport Capacity ◽  
Ribulose 1 ◽  
Electron Transportation

Abstract Background: The red (R) and blue (B) light wavelengths are known to influence many plant physiological processes during growth and development, particularly photosynthesis. To understand how R and B light influences plant photomorphogenesis and photosynthesis, we investigated changes in leaf anatomy, chlorophyll fluorescence and photosynthetic parameters, and ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) and Calvin cycle-related enzymes expression and their activities in sweet pepper ( Capsicum annuum L.) seedlings exposed to four light qualities: monochromatic white (W, control), R, B, and mixed R and B (RB) light with the same photosynthetic photon flux density (PPFD) of 300 μmol/m 2 ·s . Results: The results revealed that seedlings grown under R light had lower biomass accumulation, CO 2 assimilation, and photosystem II (PSII) electron transportation compared to plants grown under other treatments. These changes are probably due to inactivation of the photosystem (PS). Biomass accumulation and CO 2 assimilation were significantly enriched in B- and RB-grown plants, especially the latter treatment. Their leaves were also thicker, and photosynthetic electron transport capacity, as well as the photosynthetic rate were enhanced. The up-regulation of the expression and activities of Rubisco , fructose-1, 6-bisphosphatase (FBPase) and glyceraldehyde-phosphate dehydrogenase (GAPDH), which involved in the Calvin cycle and are probably the main enzymatic factors contributing to RuBP (ribulose-1, 5-bisphosphate) synthesis, were also increased. Conclusions: Mixed R and B light altered plant photomorphogenesis and photosynthesis, mainly through its effects on leaf anatomy, photosynthetic electron transportation, and the expression and activities of key Calvin cycle enzymes.

scholarly journals Mitochondrial AOX Supports Redox Balance of Photosynthetic Electron Transport, Primary Metabolite Balance, and Growth in Arabidopsis thaliana under High Light

2019 ◽  
Vol 20 (12) ◽  
pp. 3067 ◽  
Author(s):  
Zhenxiang Jiang ◽  
Chihiro K. A. Watanabe ◽  
Atsuko Miyagi ◽  
Maki Kawai-Yamada ◽  
Ichiro Terashima ◽  
...  
Keyword(s):  
Arabidopsis Thaliana ◽  
Electron Transport ◽  
Calvin Cycle ◽  
Photosynthetic Electron Transport ◽  
Tca Cycle ◽  
Mitochondrial Respiratory Chain ◽  
Redox Balance ◽  
High Light ◽  
Primary Metabolite ◽  
Physiological Importance

When leaves receive excess light energy, excess reductants accumulate in chloroplasts. It is suggested that some of the reductants are oxidized by the mitochondrial respiratory chain. Alternative oxidase (AOX), a non-energy conserving terminal oxidase, was upregulated in the photosynthetic mutant of Arabidopsis thaliana, pgr5, which accumulated reductants in chloroplast stroma. AOX is suggested to have an important role in dissipating reductants under high light (HL) conditions, but its physiological importance and underlying mechanisms are not yet known. Here, we compared wild-type (WT), pgr5, and a double mutant of AOX1a-knockout plant (aox1a) and pgr5 (aox1a/pgr5) grown under high- and low-light conditions, and conducted physiological analyses. The net assimilation rate (NAR) was lower in aox1a/pgr5 than that in the other genotypes at the early growth stage, while the leaf area ratio was higher in aox1a/pgr5. We assessed detailed mechanisms in relation to NAR. In aox1a/pgr5, photosystem II parameters decreased under HL, whereas respiratory O2 uptake rates increased. Some intermediates in the tricarboxylic acid (TCA) cycle and Calvin cycle decreased in aox1a/pgr5, whereas γ-aminobutyric acid (GABA) and N-rich amino acids increased in aox1a/pgr5. Under HL, AOX may have an important role in dissipating excess reductants to prevent the reduction of photosynthetic electron transport and imbalance in primary metabolite levels.

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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