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- Frenkel, Martin, et al.
(författare)
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Improper excess light energy dissipation in Arabidopsis results in a metabolic reprogramming
- 2009
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Ingår i: BMC Plant Biology. - : Springer Science and Business Media LLC. - 1471-2229. ; 9:12, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- Background: Plant performance is affected by the level of expression of PsbS, a key photoprotective protein involved in the process of feedback de-excitation (FDE), or the qE component of non-photochemical quenching, NPQ. Results: In studies presented here, under constant laboratory conditions the metabolite profiles of leaves of wild-type Arabidopsis thaliana and plants lacking or overexpressing PsbS were very similar, but under natural conditions their differences in levels of PsbS expression were associated with major changes in metabolite profiles. Some carbohydrates and amino acids differed ten-fold in abundance between PsbS-lacking mutants and over-expressers, with wild-type plants having intermediate amounts, showing that a metabolic shift had occurred. The transcriptomes of the genotypes also varied under field conditions, and the genes induced in plants lacking PsbS were similar to those reportedly induced in plants exposed to ozone stress or treated with methyl jasmonate (MeJA). Genes involved in the biosynthesis of JA were up-regulated, and enzymes involved in this pathway accumulated. JA levels in the undamaged leaves of field-grown plants did not differ between wild-type and PsbS-lacking mutants, but they were higher in the mutants when they were exposed to herbivory. Conclusion: These findings suggest that lack of FDE results in increased photooxidative stress in the chloroplasts of Arabidopsis plants grown in the field, which elicits a response at the transcriptome level, causing a redirection of metabolism from growth towards defence that resembles a MeJA/JA response.
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| 2. |
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| 3. |
- Ganeteg, Ulrika, et al.
(författare)
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Is each light-harvesting complex protein important for plant fitness?
- 2004
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Ingår i: Plant Physiology. - Rockville, Md. : American Society of Plant Physiologists. - 0032-0889 .- 1532-2548. ; 134:1, s. 502-509
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 5. |
- Külheim, Carsten, 1976-
(författare)
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The significance of feedback de-excitation
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 6. |
- Külheim, Carsten, et al.
(författare)
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What leads to reduced fitness in non-photochemical quenching mutants?
- 2005
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Ingår i: Physiologia Plantarum. - Oxford : Blackwell. - 1399-3054 .- 0031-9317. ; 125:2, s. 202-211
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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