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Vitamin B6 as a potential antioxidant: a study emanating from UV-B-stressed plants
Örebro University, Department of Natural Sciences.
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Increased influx of solar UV-B radiation (280-320 nm), due to a decreasing stratospheric ozone layer, impacts severely on plants. Some of the UV-B effects on plants are related to stress induced by produced reactive oxygen species (ROS). Pyridoxine (vitamin B6) has been reported to be a potential quencher of ROS.

Previous studies have shown that the PDX1.3 gene (encoding a key enzyme in vitamin B6 biosynthesis) is up-regulated by UV-B. We showed that this up-regulation also occurs at the protein level in UV-B exposed Col-0 wild-type plants. Studies performed using pdx1 knock-out mutants of Arabidopsis thaliana showed elevated transcripts levels for LHCB1*3 and PR-5 compared with the Col-0 wild-type. The pdx1 knock-out mutants showed an increased sensitivity towards H2O2-stress, but no increased sensitivity towards low dose UV-B-stress.

To study the postulated role of pyridoxine as quencher of ROS in more detail, both theoretical and experimental studies were performed. Theoretical and experimental UV absorption spectra obtained at different protonation/deprotonation states of pyridoxine showed a very close resemblance at low and high pH. However, for the computational studies at physiological pH addition of counterions were required to accurately describe the experimental spectra.

When theoretically studying the reactivity of pyridoxine towards three different ROS, .OH, .OOH and .O2-, the hydroxyl radical (.OH) was shown to be the most reactive species, while the superoxide radical (.O2-) showed no reactivity towards pyridoxine.

In order to study the role of G-proteins in UV-B signal transduction pathways, UV-B irradiated G-protein mutants of Arabidopsis thaliana were studied. The regulation of the PDX1.3 gene was not affected in the G-protein mutants, regardless of the developmental stage of the plant. However, the expression of CHS was affected in the Ga subunit mutants.

Place, publisher, year, edition, pages
Örebro: Örebro universitetsbibliotek , 2006. , p. 73
Series
Örebro Studies in Life Science ; 3
Keywords [en]
Arabidopsis, UV-B irradiation, pyridoxine, vitamin B6, ROS
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
URN: urn:nbn:se:oru:diva-625ISBN: 91-7668-497-0 (print)OAI: oai:DiVA.org:oru-625DiVA, id: diva2:137031
Public defence
2006-10-12, HSL3, Örebro universitet, Örebro, 10:00 (English)
Opponent
Supervisors
Available from: 2006-09-21 Created: 2006-09-18 Last updated: 2017-10-18Bibliographically approved
List of papers
1. The role of the pyridoxine (vitamin B6) biosynthesis enzyme PDX1 in ultraviolet-B radiation responses in plants
Open this publication in new window or tab >>The role of the pyridoxine (vitamin B6) biosynthesis enzyme PDX1 in ultraviolet-B radiation responses in plants
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2011 (English)In: Plant physiology and biochemistry (Paris), ISSN 0981-9428, E-ISSN 1873-2690, Vol. 49, no 3, p. 284-292Article in journal (Refereed) Published
Abstract [en]

Ultraviolet-B radiation regulates plant growth and morphology at low and ambient fluence rates but can severely impact on plants at higher doses. Some plant UV-B responses are related to the formation of reactive oxygen species (ROS) and pyridoxine (vitamin B6) has been reported to be a quencher of ROS. UV-B irradiation of Arabidopsis Col-0 plants resulted in increased levels of PDX1 protein, compared with UV-A-exposed plants. This was shown by immunoblot analysis using specific polyclonal antibodies raised against the recombinant PDX1.3 protein and confirmed by mass spectrometry analysis of immunoprecipitated PDX1. The protein was located mainly in the cytosol but also to a small extent in the membrane fraction of plant leaves. Immunohistochemical analysis performed in pea revealed that PDX1 is present in UV-B-exposed leaf mesophyll and palisade parenchyma but not in epidermal cells. Pyridoxine production increased in Col-0 plants exposed to 3 days of UV-B, whereas in an Arabidopsis pdx1.3 mutant UV-B did not induce pyridoxine biosynthesis. In gene expression studies performed after UV-B exposure, the pdx1.3 mutant showed elevated transcript levels for the LHCB1*3 gene (encoding a chlorophyll a/b-binding protein of the photosystem II light-harvesting antenna complex) and the pathogenesis-related protein 5 (PR-5) gene, compared with wild type.

Place, publisher, year, edition, pages
Amsterdam: Elsevier, 2011
National Category
Biochemistry and Molecular Biology
Research subject
Biochemistry
Identifiers
urn:nbn:se:oru:diva-3111 (URN)10.1016/j.plaphy.2011.01.003 (DOI)000288777300008 ()21288732 (PubMedID)2-s2.0-79951683043 (Scopus ID)
Note

This is a pre-print article

Available from: 2012-08-07 Created: 2006-09-21 Last updated: 2018-05-02Bibliographically approved
2. pH-dependent electronic and spectroscopic properties of pyridoxine (vitamin B6)
Open this publication in new window or tab >>pH-dependent electronic and spectroscopic properties of pyridoxine (vitamin B6)
2006 (English)In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 110, no 33, p. 16774-16780Article in journal (Refereed) Published
Abstract [en]

The key electronic and spectroscopic properties of vitamin B6 (pyridoxine) and some of its main charged and protonated/deprotonated species are explored using hybrid density functional theory (DFT) methods including polarized solvation models. It is found that the dominant species at low pH is the N1-protonated form and, at high pH, the O3¢-deprotonated compound. Computed and experimental UV-spectra for these species (experimental spectra recorded at pH 1.7 and 11.1, respectively) show a very close resemblance. At pH 4.3, the protonated species dominates, but with onset of the zwitterionic oxo form which is also the dominant species at neutral pH. The computational studies furthermore show that neither a polarized continuum model of the polar aqueous solvent or explicit hydrogen bonding through additional water molecules are sufficient to describe accurately the spectrum at physiological pH. Instead, Na+ and Cl- counterions were required to give a blue-shift of approximately 0.15 eV.

Keywords
Electrons, Hydrogen-Ion Concentration, Molecular Structure, Pyridoxine/*chemistry, Quantum Theory, Solvents/chemistry, Spectrum Analysis, Thermodynamics, Vitamin B 6/*chemistry, Vitamin B Complex/chemistry, Water/chemistry
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3112 (URN)10.1021/jp062800n (DOI)
Available from: 2006-09-21 Created: 2006-09-21 Last updated: 2017-12-14Bibliographically approved
3. Theoretical study of the antioxidant properties of pyridoxine
Open this publication in new window or tab >>Theoretical study of the antioxidant properties of pyridoxine
2006 (English)In: Journal of Physical Chemistry A, ISSN 1089-5639, E-ISSN 1520-5215, Vol. 110, no 48, p. 13068-13072Article in journal (Refereed) Published
Abstract [en]

Molecules acting as antioxidants capable of scavenging reactive oxygen species (ROS) are of utmost importance in the living cell. The antioxidative properties of pyridoxine (vitamin B6) have recently been discovered. In this study, we have analyzed the reactivity of pyridoxine toward the ROS .OH, .OOH, and .O2- at the density functional theory level (functionals B3LYP and MPW1B95). Two reaction types have been studied as follows: addition to the aromatic ring atoms and hydrogen/proton abstraction. Our results show that .OH is the most reactive species, while .OOH displays low reactivity and .O2- does not react at all with pyridoxine. The most exergonic reactions are those where .H is removed from the CH2OH groups or the ring-bound OH group and range from -33 to -39 kcal/mol. The most exergonic addition reactions occur by attacking the carbon atoms bonded to nitrogen but with an energy gain of only 6 kcal/mol.

Place, publisher, year, edition, pages
Washington, DC: American Chemical Society, 2006
National Category
Natural Sciences Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3113 (URN)10.1021/jp065115p (DOI)17134167 (PubMedID)
Available from: 2006-09-21 Created: 2006-09-21 Last updated: 2017-12-14Bibliographically approved
4. The role of heterotrimeric G-proteins in ultraviolet-B-stress in Arabidopsis thaliana
Open this publication in new window or tab >>The role of heterotrimeric G-proteins in ultraviolet-B-stress in Arabidopsis thaliana
(English)Manuscript (Other academic)
National Category
Chemical Sciences
Research subject
Chemistry
Identifiers
urn:nbn:se:oru:diva-3114 (URN)
Available from: 2006-09-21 Created: 2006-09-21 Last updated: 2017-10-18Bibliographically approved

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