The catalytic oxidation of p-xylene is investigated, focusing on the chemistry and kinetics responsible for it. Another focus is the industrial processing of terephthalic acid and an overview of ...hydrocarbon oxidation.
Summary
The extracytoplasmic function sigma factor σT is the master regulator of general stress response in Caulobacter crescentus and controls the expression of its paralogue σU. In this work we ...showed that PhyR and NepR act, respectively, as positive and negative regulators of σT expression and function. Biochemical data also demonstrated that NepR directly binds σT and the phosphorylated form of PhyR. We also described the essential role of the histidine kinase gene CC3474, here denominated phyK, for expression of σT‐dependent genes and for resistance to stress conditions. Additionally, in vivo evidence of PhyK‐dependent phosphorylation of PhyR is presented. This study also identified a conserved cysteine residue (C95) located in the periplasmic portion of PhyK that is crucial for the function of the protein. Furthermore, we showed that PhyK, PhyR and σT regulate the same set of genes and that σT apparently directly controls most of its regulon. In contrast, σU seems to have a very modest contribution to the expression of a subset of σT‐dependent genes. In conclusion, this report describes the molecular mechanism involved in the control of general stress response in C. crescentus.
Nucleoid-associated proteins (NAPs) are DNA binding proteins critical for the organization and function of the bacterial chromosome. A newly discovered NAP in
, GapR, is thought to facilitate the ...movement of the replication and transcription machines along the chromosome by stimulating type II topoisomerases to remove positive supercoiling. Here, utilizing genetic, biochemical, and biophysical studies of GapR in light of a recently published DNA-bound crystal structure of GapR, we identified the structural elements involved in oligomerization and DNA binding. Moreover, we show that GapR is maintained as a tetramer upon its dissociation from DNA and that tetrameric GapR is capable of binding DNA molecules
Analysis of protein chimeras revealed that two helices of GapR are functionally conserved in H-NS, demonstrating that two evolutionarily distant NAPs with distinct mechanisms of action utilize conserved structural elements to oligomerize and bind DNA.
Bacteria organize their genetic material in a structure called the nucleoid, which needs to be compact to fit inside the cell and, at the same time, dynamic to allow high rates of replication and transcription. Nucleoid-associated proteins (NAPs) play a pivotal role in this process, so their detailed characterization is crucial for our understanding of DNA organization into bacterial cells. Even though NAPs affect DNA-related processes differently, all of them have to oligomerize and bind DNA for their function. The significance of this study is the identification of structural elements involved in the oligomerization and DNA binding of a newly discovered NAP in
and the demonstration that structural elements are conserved in evolutionarily distant and functionally distinct NAPs.
It has been shown that gibberellin (GA) perception is part of root-to-shoot communication in plants during drought. However, it is not clear how GA content interferes with long-distance drought ...response signaling. Thus, in this study, the tomato (
Solanum lycopersicum
L.) cultivar Micro-Tom (MT) was treated with 50 mM acid gibberellic, while the control plants were sprayed with water. After treatment, tomato plants were reciprocally grafted (i.e., MT/MT, MT + GA/MT + GA, MT + GA/MT, MT/MT + GA; within each pair, the first indicates the scion, and the second indicates the rootstock). Therefore, to evaluate the role of GA in root-to-shoot communication during drought stress, plants were grown under well-watered or drought conditions. Height, leaf and root area, dry weight, malondialdehyde content, relative water content and stomatal conductance were measured. It was verified that the MT + GA/MT and MT + GA/MT + GA plants were taller than the grafted plants without GA treatment. Furthermore, non-treated plants (MT/MT) exhibited a reduction in root area due to water-deficit. Regarding water relations, under drought, the greatest reduction in stomatal conductance was observed in plants grafted onto rootstocks treated with GA, which favored the maintenance of an increased relative water content. This demonstrates an important role of GA in root-to-shoot communication to induce stomatal closure during water-deficit conditions.
Chronic lead exposure induces hypertension and alters endothelial function. However, treatment with low lead concentrations was not yet explored. We analyzed the effects of 7 day exposure to low lead ...concentrations on endothelium-dependent responses. Wistar rats were treated with lead (1st dose 4 µg/100 g, subsequent dose 0.05 µg/100 g, i.m. to cover daily loss) or vehicle; blood levels attained at the end of treatment were 9.98 µg/dL. Lead treatment had the following effects: increase in systolic blood pressure (SBP); reduction of contractile response to phenylephrine (1 nM-100 µM) of aortic rings; unaffected relaxation induced by acetylcholine (0.1 nM-300 µM) or sodium nitroprusside (0.01 nM-0.3 µM). Endothelium removal, N(G)-nitro-L-arginine methyl ester (100 µM) and tetraethylammonium (2 mM) increased the response to phenylephrine in treated rats more than in untreated rats. Aminoguanidine (50 µM) increased but losartan (10 µM) and enalapril (10 µM) reduced the response to phenylephrine in treated rats. Lead treatment also increased aortic Na(+)/K(+)-ATPase functional activity, plasma angiotensin-converting enzyme (ACE) activity, protein expression of the Na(+)/K(+)-ATPase alpha-1 subunit, phosphorylated endothelial nitric oxide synthase (p-eNOS), and inducible nitric oxide synthase (iNOS). Our results suggest that on initial stages of lead exposure, increased SBP is caused by the increase in plasma ACE activity. This effect is accompanied by increased p-eNOS, iNOS protein expression and Na(+)/K(+)-ATPase functional activity. These factors might be a compensatory mechanism to the increase in SBP.
Chronic lead exposure causes hypertension and cardiovascular disease. Our purpose was to evaluate the effects of acute exposure to lead on arterial pressure and elucidate the early mechanisms ...involved in the development of lead-induced hypertension.
Wistar rats were treated with lead acetate (i.v. bolus dose of 320 µg/Kg), and systolic arterial pressure, diastolic arterial pressure and heart rate were measured during 120 min. An increase in arterial pressure was found, and potential roles of the renin-angiotensin system, Na(+),K(+)-ATPase and the autonomic reflexes in this change in the increase of arterial pressure found were evaluated. In anesthetized rats, lead exposure: 1) produced blood lead levels of 37±1.7 µg/dL, which is below the reference blood concentration (60 µg/dL); 2) increased systolic arterial pressure (Ct: 109±3 mmHg vs Pb: 120±4 mmHg); 3) increased ACE activity (27% compared to Ct) and Na(+),K(+)-ATPase activity (125% compared to Ct); and 4) did not change the protein expression of the α1-subunit of Na(+),K(+)-ATPase, AT(1) and AT(2). Pre-treatment with an AT(1) receptor blocker (losartan, 10 mg/Kg) or an ACE inhibitor (enalapril, 5 mg/Kg) blocked the lead-induced increase of arterial pressure. However, a ganglionic blockade (hexamethonium, 20 mg/Kg) did not prevent lead's hypertensive effect.
Acute exposure to lead below the reference blood concentration increases systolic arterial pressure by increasing angiotensin II levels due to ACE activation. These findings offer further evidence that acute exposure to lead can trigger early mechanisms of hypertension development and might be an environmental risk factor for cardiovascular disease.
In this work we investigated whether priming with auxin, cytokinin, gibberellin, abscisic acid and ethylene, alters the physiological responses of seeds of pigeon pea germinated under water and ...cadmium stress. Seeds treated with water or non-treated seeds were used as control. Although compared to non-treated seeds we found that the hormone treatments improve the germination of pigeon pea under cadmium stress, however, these treatments did not differ from water. However, we also observed a trend of tolerance to the effects of cadmium in the presence of ethylene, suggesting that the use of this hormone may be an efficient method to overcome seed germination under metal stress.
▶ We used the ethylene-insensitive Never ripe (Nr) tomato (Solanum lycopersicum L.) mutant and Micro-Tom, which blocks ethylene responses, to investigate the oxidative stress responses to Cd and ...NaCl. ▶ Similar growth patterns and Na and Cd accumulation for MT and Nr were observed but the mutant exhibited reduced leaf chlorophyll degradation following stress. ▶ One specific superoxide isoenzyme from roots responded differently to NaCl and CdCl2 exposure, but was not genotype specific. ▶ Overall the results indicate that the ethylene signaling associated with NR receptor can modulate the biochemical pathways of oxidative stress in a tissue dependent manner, and that this signaling may be different following Na and Cd exposure.
In order to further address the known interaction between ethylene and components of the oxidative system, we have used the ethylene-insensitive Never ripe (Nr) tomato (Solanum lycopersicum L.) mutant, which blocks ethylene responses. The mutant was compared to the control Micro-Tom (MT) cultivar subjected to two stressful situations: 100mM NaCl and 0.5mM CdCl2. Leaf chlorophyll, lipid peroxidation and antioxidant enzyme activities in roots, leaves and fruits, and Na and Cd accumulation in tissues were determined. Although we verified a similar growth pattern and Na and Cd accumulation for MT and Nr, the mutant exhibited reduced leaf chlorophyll degradation following stress. In roots and leaves, the patterns of catalase (CAT), glutathione reductase (GR), ascorbate peroxidase (APX), guaiacol peroxidase (GPOX), superoxide dismutase (SOD) enzyme activity as well as malondialdehyde (MDA) and hydrogen peroxide (H2O2) production under the stressful conditions tested were very similar between MT and Nr mutant. However, Nr fruits showed increased H2O2 production, reduced and enhanced APX activity in NaCl and CdCl2, respectively, and enhanced GPOX in NaCl. Moreover, through non-denaturing PAGE, a similar reduction of SOD I band intensity in both, control MT and Nr mutant, treated with NaCl was observed. In leaves and fruits, a similar SOD activity pattern was observed for all periods, genotypes and treatments. Overall the results indicate that the ethylene signaling associated with NR receptor can modulate the biochemical pathways of oxidative stress in a tissue dependent manner, and that this signaling may be different following Na and Cd exposure.
The tomato (Solanum lycopersicum L.) plant is both an economically important food crop and an ideal dicot model to investigate various physiological phenomena not possible in Arabidopsis thaliana. ...Due to the great diversity of tomato cultivars used by the research community, it is often difficult to reliably compare phenotypes. The lack of tomato developmental mutants in a single genetic background prevents the stacking of mutations to facilitate analysis of double and multiple mutants, often required for elucidating developmental pathways.
We took advantage of the small size and rapid life cycle of the tomato cultivar Micro-Tom (MT) to create near-isogenic lines (NILs) by introgressing a suite of hormonal and photomorphogenetic mutations (altered sensitivity or endogenous levels of auxin, ethylene, abscisic acid, gibberellin, brassinosteroid, and light response) into this genetic background. To demonstrate the usefulness of this collection, we compared developmental traits between the produced NILs. All expected mutant phenotypes were expressed in the NILs. We also created NILs harboring the wild type alleles for dwarf, self-pruning and uniform fruit, which are mutations characteristic of MT. This amplified both the applications of the mutant collection presented here and of MT as a genetic model system.
The community resource presented here is a useful toolkit for plant research, particularly for future studies in plant development, which will require the simultaneous observation of the effect of various hormones, signaling pathways and crosstalk.
In order to further address the modulation of signaling pathways of stress responses and their relation to hormones, we used the ethylene-insensitive Never ripe (Nr) and the auxin-insensitive ...diageotropica (dgt) tomato mutants. The two mutants and the control Micro-Tom (MT) cultivar were grown over a 40-day period in the presence of Cd (0.2 mM CdCl2 and 1 mM CdCl2). Lipid peroxidation, leaf chlorophyll, proline content, Cd content and antioxidant enzyme activities in roots, leaves and fruits were determined. The overall results indicated that the MT genotype had the most pronounced Cd damage effects while Nr and dgt genotypes might withstand or avoid stress imposed by Cd. This fact may be attributed, at least in part, to the fact that the known auxin-stimulated ethylene production is comprised in dgt plants. Conversely, the Nr genotype was more affected by the Cd imposed stress than dgt, which may be explained by the fact that Nr retains a partial sensitivity to ethylene. These results add further information that should help unraveling the relative importance of ethylene in regulating the cell responses to stressful conditions.
► The Micro-Tom genotype is more sensitive to Cd-induced stress. ► Nr and dgt mutants withstand more efficiently the oxidative stress imposed by Cd. ► Nr was more affected than dgt possibly because it retains partial sensitivity to ethylene.
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