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The significance of feedback de-excitation
Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During photosynthesis sunlight is absorbed by photosynthetic pigments and converted into organic compounds, such as carbohydrates. Photosynthesis needs to be highly regulated, since both too much and too little light are harmful to plant. If too little light is absorbed, a plant cannot store enough energy, which will have effects on growth and fitness of the plant. With too much light absorbed, a dangerous side reaction of photosynthesis, the production of reactive oxygen species can happen. These reactive oxygen species can damage the proteins in the chloroplast and the lipids of the chloroplast.

To avoid the production of reactive oxygen species, plants have evolved many mechanisms, which act on different time-scales and different levels of organization. As a first measure, when the absorbed light is exceeding the capacity for its utilization, is to switch the light-harvesting antenna from efficient light harvesting to energy dissipation. This process is called feedback de-excitation (FDE). The protein PsbS is essential for this process as well as a functioning xanthophylls cycle with the enzyme violaxanthin de-epoxidase (VDE).

I have investigated the effects of plants with changes in their ability to dissipate excess excitation energy in the model plants species Arabidopsis thaliana. Three genotypes with either increased or decreased capacity for FDE were used during my experiments. The first genotype over-expresses the PsbS gene, having approximately two-fold increased amounts of PsbS and FDE. The second is a PsbS deletion mutant with no PsbS protein and no FDE. The third genotype cannot perform the conversion of violaxanthin to zeaxanthin, because the enzyme VDE is missing. This mutant has some FDE left.

Arabidopsis thaliana is an annual plant, which flowers only once in its lifetime. Therefore, when counting the seeds produced an estimation of fitness can be made from the amount of seeds produced. This was done during my experiments and shown that FDE is a trait and that plants with increased FDE have a higher fitness and vice versa.

This was also the case for a collection of plants lacking a single protein from the light harvesting antenna. All of these genotypes had a fitness reduction, proving that their function is not redundant.

In an attempt to explain why the fitness is reduced in plants with altered FDE, photosynthetic measurements, as well as a determination of the transcriptome and the metabolome was performed. Plants lacking FDE had higher levels of photoinhibition, leading both to lower rates of photosynthesis and to higher repair cost. This could in part explain the reduction in fitness. These plants also had major changes in their transcriptome and their metabolome. Primary metabolism was most effected, for example carbohydrate and amino acid metabolism. But there were also changes in secondary metabolism such as an up regulation of the biosynthesis of anthocyanins.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik , 2005. , 59 p.
Keyword [en]
Arabidopsis thaliana, photosynthesis, feedback de-excitation, fitness, metabolomics, transcriptomics
National Category
Botany
Identifiers
URN: urn:nbn:se:umu:diva-581ISBN: 91-7305-931-5 (print)OAI: oai:DiVA.org:umu-581DiVA: diva2:143861
Public defence
2005-09-23, 00:00
Available from: 2005-09-05 Created: 2005-09-05 Last updated: 2011-03-10Bibliographically approved
List of papers
1. Is each light-harvesting complex protein important for plant fitness?
Open this publication in new window or tab >>Is each light-harvesting complex protein important for plant fitness?
2004 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 134, no 1, 502-509 p.Article in journal (Refereed) Published
Abstract [en]

Many of the photosynthetic genes are conserved among all higher plants, indicating that there is strong selective pressure to maintain the genes of each protein. However, mutants of these genes often lack visible growth phenotypes, suggesting that they are important only under certain conditions or have overlapping functions. To assess the importance of specific genes encoding the light-harvesting complex (LHC) proteins for the survival of the plant in the natural environment, we have combined two different scientific traditions by using an ecological fitness assay on a set of genetically modified Arabidopsis plants with differing LHC protein contents. The fitness of all of the LHC-deficient plants was reduced in some of the growth environments, supporting the hypothesis that each of the genes has been conserved because they provide ecological flexibility, which is of great adaptive value given the highly variable conditions encountered in nature.

Place, publisher, year, edition, pages
Rockville, Md.: American Society of Plant Physiologists, 2004
Keyword
Arabidopsis/genetics/growth & development/*physiology, Genes; Plant, Light-Harvesting Protein Complexes/genetics/*physiology, Models; Biological, Mutation, Plant Proteins/genetics/*physiology
Identifiers
urn:nbn:se:umu:diva-11796 (URN)10.1104/pp.103.033324 (DOI)14730076 (PubMedID)
Available from: 2007-08-09 Created: 2007-08-09 Last updated: 2017-12-14Bibliographically approved
2. Rapid regulation of light harvesting and plant fitness in the field
Open this publication in new window or tab >>Rapid regulation of light harvesting and plant fitness in the field
2002 (English)In: Science, Vol. 297, 91-93 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-4661 (URN)
Available from: 2005-09-05 Created: 2005-09-05 Last updated: 2015-04-29Bibliographically approved
3. What leads to reduced fitness in non-photochemical quenching mutants?
Open this publication in new window or tab >>What leads to reduced fitness in non-photochemical quenching mutants?
2005 (English)In: Physiologia Plantarum, ISSN 1399-3054, Vol. 125, no 2, 202-211 p.Article in journal (Refereed) Published
Abstract [en]

Feedback de-excitation (FDE) is a process that protects photosystem II from damage during short periods of overexcitation. Arabidopsis thaliana mutants lacking this mechanism have reduced fitness in environments with variable light intensities. We have assayed the physiological consequences of mutations resulting in the lack of FDE and analysed the differences between field-grown plants and plants grown under fluctuating light in the laboratory. We show that FDE is an important mechanism in short-term responses to fluctuating light. Anthocyanin and carbohydrate levels indicated that the mutant plants were stressed to a higher degree than wild-type (WT) plants. Field-grown mutants were photo-inactivated to a greater degree than WT, whereas mutant plants in the fluctuating light environment in the laboratory seemed to downregulate the photosynthetic quantum yield, thereby avoiding photo-damage but resulting in impaired growth in the case of one mutant. Finally, we provide evidence that FDE is most important under conditions when photosynthesis limits plant growth, for example during flower and seed development.

Place, publisher, year, edition, pages
Oxford: Blackwell, 2005
Identifiers
urn:nbn:se:umu:diva-15949 (URN)10.1111/j.1399-3054.2005.00547.x (DOI)
Available from: 2007-08-06 Created: 2007-08-06 Last updated: 2015-04-29Bibliographically approved
4. Metabolomics and transcriptomics in the field – PsbS levels strongly influence plant metabolism
Open this publication in new window or tab >>Metabolomics and transcriptomics in the field – PsbS levels strongly influence plant metabolism
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Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-4663 (URN)
Available from: 2005-09-05 Created: 2005-09-05 Last updated: 2010-01-13Bibliographically approved
5. Previous days’ weather could determine the expression of the PsbS-gene
Open this publication in new window or tab >>Previous days’ weather could determine the expression of the PsbS-gene
Show others...
2005 (English)Manuscript (preprint) (Other academic)
National Category
Ecology Environmental Sciences
Identifiers
urn:nbn:se:umu:diva-4664 (URN)
External cooperation:
Available from: 2005-09-05 Created: 2005-09-05 Last updated: 2016-08-26Bibliographically approved

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