scholarly journals Lipoxygenase functions in 1O2 production during root responses to osmotic stress

2021 ◽  
Author(s):  
Tomer Chen ◽  
Dekel Cohen ◽  
Maxim Itkin ◽  
Sergey Malitsky ◽  
Robert Fluhr
Keyword(s):  
Linoleic Acid ◽  
Osmotic Stress ◽  
Root Growth ◽  
Lipoxygenase Inhibitor ◽  
Acid Product ◽  
Arabidopsis Root ◽  
Rate Limiting Step ◽  
Root Responses ◽  
Rate Limiting ◽  
Fatty Acid Hydroperoxides

Abstract Drought induces osmotic stress in roots, a condition simulated by the application of high-molecular-weight polyethylene glycol. Osmotic stress results in the reduction of Arabidopsis thaliana root growth and production of 1O2 from an unknown non-photosynthetic source. Reduced root growth can be alleviated by application of the 1O2 scavenger histidine. Here we examined the possibility that 1O2 production involves Russell reactions occurring among the enzymatic products of lipoxygenases, the fatty acid hydroperoxides. Lipoxygenase (LOX) activity was measured for purified soybean (Glycine max) LOX1 and in crude Arabidopsis root extracts using linoleic acid as substrate. Formation of the 13(S)-Hydroperoxy-9(Z),11(E)-octadecadienoic acid product was inhibited by salicylhdroxamic acid, which is a lipoxygenase inhibitor, but not by histidine, whereas 1O2 production was inhibited by both. D2O, which specifically extends the half-life of 1O2, augmented the lipoxygenase-dependent generation of 1O2, as expected from a Russell-type reaction. The addition of linoleic acid to roots stimulated 1O2 production and inhibited growth, suggesting that the availability of lipoxygenase substrate is a rate-limiting step. Indeed, water stress rapidly increased linoleic and linolenic acids by 2.5-fold in roots. Mutants with root-specific microRNA repression of lipoxygenases showed downregulation of lipoxygenase protein and activity. The lines with downregulated lipoxygenase displayed significantly less 1O2 formation, improved root growth in osmotic stress, and an altered transcriptome response compared to wild type. The results show that lipoxygenases can serve as an enzymatic source of ‘dark’ 1O2 during osmotic stress and demonstrate a role for 1O2 in defining the physiological response.

scholarly journals Biochemical characterization of a trypanosome enzyme with glutathione-dependent peroxidase activity

2000 ◽  
Vol 352 (3) ◽  
pp. 755-761 ◽  
Author(s):  
Shane R. WILKINSON ◽  
David J. MEYER ◽  
John M. KELLY
Keyword(s):  
Linoleic Acid ◽  
Peroxidase Activity ◽  
Biochemical Characterization ◽  
Linoleic Acid Hydroperoxide ◽  
Butyl Hydroperoxide ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Wide Range ◽  
Acid Hydroperoxide ◽  
Rate Limiting

In most eukaryotes, glutathione-dependent peroxidases play a key role in the metabolism of peroxides. Numerous studies have reported that trypanosomatids lack this activity. Here we show that this is not the case, at least for the American trypanosome Trypanosoma cruzi. We have isolated a single-copy gene from T. cruzi with the potential to encode an 18kDa enzyme, the sequence of which has highest similarity with glutathione peroxidases from plants. A recombinant form of the protein was purified following expression in Escherichia coli. The enzyme was shown to have peroxidase activity in the presence of glutathione/glutathione reductase but not in the presence of trypanothione/trypanothione reductase. It could metabolize a wide range of hydroperoxides (linoleic acid hydroperoxide and phosphatidylcholine hydroperoxide> cumene hydroperoxide>t-butyl hydroperoxide), but no activity towards hydrogen peroxide was detected. Enzyme activity could be saturated by glutathione when both fatty acid and short-chain organic hydroperoxides were used as substrate. For linoleic acid hydroperoxide, the rate-limiting step of this reaction is the reduction of the peroxidase by glutathione. With lower-affinity substrates such as t-butyl hydroperoxide, the rate-limiting step is the reduction of the oxidant. The data presented here identify a new arm of the T. cruzi oxidative defence system.

scholarly journals Natural Root Cellular Variation in Responses to Osmotic Stress in Arabidopsis thaliana Accessions

Genes ◽  
2019 ◽  
Vol 10 (12) ◽  
pp. 983 ◽  
Author(s):  
Wendy Cajero-Sanchez ◽  
Pamela Aceves-Garcia ◽  
María Fernández-Marcos ◽  
Crisanto Gutiérrez ◽  
Ulises Rosas ◽  
...  
Keyword(s):  
Osmotic Stress ◽  
Root Growth ◽  
Phenotypic Variability ◽  
Root Hairs ◽  
Stress Conditions ◽  
Root Apical Meristem ◽  
Radial Expansion ◽  
Arabidopsis Root ◽  
Cell Niche ◽  
Root Tissues

Arabidopsis naturally occurring populations have allowed for the identification of considerable genetic variation remodeled by adaptation to different environments and stress conditions. Water is a key resource that limits plant growth, and its availability is initially sensed by root tissues. The root’s ability to adjust its physiology and morphology under water deficit makes this organ a useful model to understand how plants respond to water stress. Here, we used hyperosmotic shock stress treatments in different Arabidopsis accessions to analyze the root cell morphological responses. We found that osmotic stress conditions reduced root growth and root apical meristem (RAM) size, promoting premature cell differentiation without affecting the stem cell niche morphology. This phenotype was accompanied by a cluster of small epidermal and cortex cells with radial expansion and root hairs at the transition to the elongation zone. We also found this radial expansion with root hairs when plants are grown under hypoosmotic conditions. Finally, root growth was less affected by osmotic stress in the Sg-2 accession followed by Ws, Cvi-0, and Col-0; however, after a strong osmotic stress, Sg-2 and Cvi-0 were the most resilience accessions. The sensitivity differences among these accessions were not explained by stress-related gene expression. This work provides new cellular insights on the Arabidopsis root phenotypic variability and plasticity to osmotic stress.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

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