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Control of reactive oxygen species homeostasis in response to environmental stress
Stockholm University, Faculty of Science, Department of Botany.
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Plants are exposed to various fluctuations in their environmental conditions - light intensity, temperature, water status - and have to adapt in order to survive. Plant acclimatory responses can include the formation of new tissues, e.g., aerenchyma, or the activation of defense systems, e.g., the ascorbate-glutathione cycle for detoxification of reactive oxygen species (ROS). A prominent ROS is hydrogen peroxide (H2O2), a non-radical molecule formed during the reduction of oxygen. Due to its non-radical nature, H2O2 is more stable than other ROS and this longevity makes it the most abundant ROS in the plant cell and potentially harmful. In spite of this, H2O2 is involved in several signal transduction processes in plant cells, e.g., in the control of stomatal aperture, in plant-symbiont- and in plant-pathogen interactions, also in programmed cell death (PCD). Therefore, it is important for plant cells to maintain a tight control of H2O2 levels.

In this study, the role of H2O2 production and -detoxification was studied in different plant processes. First, signaling leading to aerenchyma formation was studied in Arabidopsis thaliana. This plant shows lysigenous aerenchyma formation, a process involving PCD, which meant it was preceded by H2O2 formation. Second, the role of a H2O2 detoxifying enzyme, cytosolic ascorbate peroxidase 2 (APX2) from A. thaliana, in the local and systemic response to excess light stress, was studied by means of the characterization of APX2 knockout mutant lines. Third, antioxidant defense was studied in two types of nitrogen-fixing actinorhizal root nodules with different oxygen metabolism, from Datisca glomerata and Casuarina glauca. Fourth, the role of a plant natriuretic peptide from actinorhizal nodules of Alnus glutinosa, in abiotic stress resistance was studied.

Place, publisher, year, edition, pages
Stockholm: Department of Botany, Stockholm University , 2009. , 51 p.
Keyword [en]
Stress, antioxidant defense, ascorbate peroxidase, aerenchyma, actinorhiza
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-30849ISBN: 978-91-7155-967-8 (print)OAI: oai:DiVA.org:su-30849DiVA: diva2:274384
Public defence
2009-11-27, Föreläsningssalen, Botanicum, Lilla Frescativägen 5, Stockholm, 13:00 (English)
Opponent
Supervisors
Note
At the time of the doctoral defence, the following papers were unpublished and had a status as follows: Paer 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.Available from: 2009-11-05 Created: 2009-10-28 Last updated: 2009-10-29Bibliographically approved
List of papers
1. Lysigenous Aerenchyma Formation in Arabidopsis is Controlled by LESION SIMULATING DISEASE1
Open this publication in new window or tab >>Lysigenous Aerenchyma Formation in Arabidopsis is Controlled by LESION SIMULATING DISEASE1
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2007 (English)In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 19, no 11, 3819-3830 p.Article in journal (Refereed) Published
Abstract [en]

Aerenchyma tissues form gas-conducting tubes that provide rootswith oxygen under hypoxic conditions. Although aerenchyma havereceived considerable attention in Zea mays, the signaling eventsand genes controlling aerenchyma induction remain elusive. Here,we show that Arabidopsis thaliana hypocotyls form lysigenousaerenchyma in response to hypoxia and that this process involvesH2O2 and ethylene signaling. By studying Arabidopsis mutantsthat are deregulated for excess light acclimation, cell death,and defense responses, we find that the formation of lysigenousaerenchyma depends on the plant defense regulators LESION SIMULATINGDISEASE1 (LSD1), ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1), andPHYTOALEXIN DEFICIENT4 (PAD4) that operate upstream of ethyleneand reactive oxygen species production. The obtained resultsindicate that programmed cell death of lysigenous aerenchymain hypocotyls occurs in a similar but independent manner fromthe foliar programmed cell death. Thus, the induction of aerenchymais subject to a genetic and tissue-specific program. The datalead us to conclude that the balanced activities of LSD1, EDS1,and PAD4 regulate lysigenous aerenchyma formation in responseto hypoxia.

Keyword
programmed cell death, hydrogen peroxide, ethylene
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-30830 (URN)10.1105/tpc.106.048843 (DOI)000252268700036 ()
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2017-12-12Bibliographically approved
2. A natriuretic peptide is formed at high levels in actinorhizal nodules of Alnus glutinosa
Open this publication in new window or tab >>A natriuretic peptide is formed at high levels in actinorhizal nodules of Alnus glutinosa
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Plant homologues of mammalian natriuretic peptides (Plant Natriuretic Peptides, PNPs, also called γ-expansins as they represent expansins lacking the third exon/C-terminal domain) are small apoplastic proteins that have been associated with various biotic and abiotic stresses. Here, the characterization of PNP from Alnus glutinosa is described that is expressed at high levels in actinorhizal root nodules induced by nitrogen-fixing Frankia, and at very low levels during fruit development. In order to determine the function of this PNP in nodules, the cDNA was expressed in transgenic tobacco under control of the CaMV35S promoter. The results reveal a very slight increase in resistance to oxidative/nitrosative stress. Based on the occurrence of PNPs in different types of nitrogen-fixing root nodules and the oxidative/nitrosative stress these nodule types are exposed to, we hypothesize that Ag67 is involved in the response to nitric oxide.

Keyword
Frankia, actinorhiza, nodulin, ectopic expression
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-30844 (URN)
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-01-14
3. Salt stress responses in nodules of two actinorhizal plant species, Datisca glomerata and Casuarina glauca
Open this publication in new window or tab >>Salt stress responses in nodules of two actinorhizal plant species, Datisca glomerata and Casuarina glauca
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Soil salinization is a factor in declining crop yields worldwide. Salt tolerance depends on the plant antioxidant defense system. Nitrogen availability is essential to agriculture and land reclamation. Some nitrogen-fixing bacteria can enter symbioses with higher plants - rhizobia with legumes, and Frankia strains with actinorhizal plants. In both symbioses, the plants form special organs, root nodules, wherein they host the bacterial endosymbionts. Rhizobial nitrogen fixation in legume nodules in combination with the oxygen protection system, leads to the production of reactive oxygen species (ROS) which require a high activity of antioxidant defense, a fact which has been thought to be responsible for the salt sensitivity of legumes. Actinorhizal oxygen protection systems for bacterial nitrogen fixation in nodules are more diverse, and actinorhizal plants tend to show salt tolerance. In this study, the antioxidant defense systems were examined in two actinorhizal species, Casuarina glauca which has an oxygen protection system similar to those of legumes, and Datisca glomerata which has a different system. The results indicated that the subcellular location of hydrogen peroxide production differed in infected cells of both plants, namely, the cytosol in C. glauca and the symbiotic bacteria in D. glomerata.  Studies of enzymes and metabolites involved in antioxidant defense indicated that the glutathione-ascorbate cycle is far more active in D. glomerata than in C. glauca nodules, while the latter have higher catalase activities.

Keyword
reactive oxygen species, antioxidant system, ascorbate peroxidase, glutathione
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-30846 (URN)
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-01-14
4. The role of ASCORBATE PEROXIDASE 2 in systemic signaling in Arabidopsis thaliana
Open this publication in new window or tab >>The role of ASCORBATE PEROXIDASE 2 in systemic signaling in Arabidopsis thaliana
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Plants have to survive in a changing environment and adapt to different abiotic stresses like changes in light intensity or temperature, flooding and soil salinity. Stress conditions cause the increased production of reactive oxygen species (ROS). ROS detoxification requires the activity of different antioxidant systems, among them the H2O2 scavenging enzymes, ascorbate peroxidases (APXs). Many APX forms exist; specifically, a cytosolic APX2 whose expression is restricted to bundle sheath cells and is induced upon accumulation of H2O2 in the chloroplasts of these cells. While the regulation of APX2 expression is well examined, not much is known about its function. Here, the characterization of two APX2 knockout lines from Arabidopsis thaliana is described. The results indicated that APX2 activity does not affect resistance against excess light stress, but systemic signaling in response to excess light treatment.

Keyword
reactive oxygen species, light stress, bundle sheath cells
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-30833 (URN)
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-01-14

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