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Salt stress responses in nodules of two actinorhizal plant species, Datisca glomerata and Casuarina glauca
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
Stockholm University, Faculty of Science, Department of Botany.
(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 [en]
reactive oxygen species, antioxidant system, ascorbate peroxidase, glutathione
National Category
Botany
Research subject
Plant Physiology
Identifiers
URN: urn:nbn:se:su:diva-30846OAI: oai:DiVA.org:su-30846DiVA: diva2:274362
Available from: 2009-10-28 Created: 2009-10-28 Last updated: 2010-01-14
In thesis
1. Control of reactive oxygen species homeostasis in response to environmental stress
Open this publication in new window or tab >>Control of reactive oxygen species homeostasis in response to environmental stress
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
Stress, antioxidant defense, ascorbate peroxidase, aerenchyma, actinorhiza
National Category
Botany
Research subject
Plant Physiology
Identifiers
urn:nbn:se:su:diva-30849 (URN)978-91-7155-967-8 (ISBN)
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

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