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The light-harvesting antenna of higher plant photosystem I
Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

During photosynthesis, two multi-protein complexes, photosystems (PS) I and II work in tandem to convert the light-energy absorbed by the light-harvesting antennae into chemical energy, which is subsequently used to assimilate atmospheric carbon dioxide into organic carbon compounds. This is the main nutritional basis for life on Earth.

The photosynthetic antenna of higher plants comprises at least ten different pigment-binding proteins (LHC), which play important roles in photosynthesis. Chlorophyll and carotenoid molecules associated with the LHC proteins are organised into an array, which can be modulated, thereby optimising light-harvesting processes and protection against oxidative damage under conditions of excessive light absorption. All ten LHC proteins have been conserved through eons of evolution, suggesting that there are strong evolutionary pressures to retain all ten proteins, and hence that each protein has a unique function.

The light-harvesting antenna of higher plant PSI consists of at least four proteins, Lhca1-4, collectively called LHCI. By constructing transgenic Arabidopsis thaliana plants in which each Lhca gene has been individually repressed or knocked-out, a collection of plants with different Lhca protein contents was obtained. The objective was to use these plants to study the structure, function and regulation of the Lhca proteins in vivo. The major findings of this work are as follows.

Removing single Lhca proteins influenced the stability of the other Lhca proteins, showing that there is a high degree of inter-dependency between the polypeptides in LHCI, and hence that a full set of Lhca proteins is important for maintaining the structural integrity of LHCI. This has provided insight into the organisation of LHCI by revealing clues about the relative positions of each Lhca protein in the antenna complex. The physiological consequences of removing individual Lhca proteins were dependent on the degree of antenna depletion. Plants with relatively small antenna changes could compensate, to some extent, for the loss of LHCI, while larger depletions had profound effects on whole plant resulting in growth reductions.

The fitness of each Lhca plant was assessed by measuring their seed production in the harsh conditions in the field. We found that all Lhca-deficient plants produced fewer seeds under some conditions, with seed-production compared to wild type varying between 10-80% depending on the extent of LHCI reduction. Therefore, we conclude that each Lhca protein is important for plant fitness, and hence for the survival of the species.

PSI is characterised by a pool of pigments absorbing light in the red end of the solar visible spectrum, thought to be especially important for plants in dense vegetation systems where the incident light is enriched in wavelengths higher than 690 nm. A majority of these pigments are situated on LHCI and, based on in-vitro studies, were thought to be mainly associated with Lhca4. Using our plants, we have established that red pigments are indeed present on all Lhca proteins and that these pigments become even more red upon association with PSI.

Place, publisher, year, edition, pages
Umeå: Umeå universitet , 2004. , 67 p.
Keyword [en]
Plant physiology, antisense, Arabidopsis thaliana, chlorophyll, fitness, LHC, photosynthesis
Keyword [sv]
Växtfysiologi
National Category
Botany
Identifiers
URN: urn:nbn:se:umu:diva-209ISBN: 91-7305-625-1 (print)OAI: oai:DiVA.org:umu-209DiVA: diva2:142652
Public defence
2004-04-02, Umeå, 10:00
Available from: 2004-03-12 Created: 2004-03-12 Last updated: 2011-03-10Bibliographically approved
List of papers
1. The properties of the chlorophyll a/b-binding proteins Lhca2 and Lhca3 studied in vivo using antisense inhibition
Open this publication in new window or tab >>The properties of the chlorophyll a/b-binding proteins Lhca2 and Lhca3 studied in vivo using antisense inhibition
2001 (English)In: Plant Physiol, Vol. 127, 150-158 p.Article in journal (Refereed) Published
Identifiers
urn:nbn:se:umu:diva-3779 (URN)
Available from: 2004-03-12 Created: 2004-03-12 Last updated: 2015-05-06Bibliographically approved
2. 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: 2015-04-29Bibliographically approved
3. Lhca5 - an LHC-type protein associated with photosystem I.
Open this publication in new window or tab >>Lhca5 - an LHC-type protein associated with photosystem I.
Article in journal (Refereed) Submitted
Identifiers
urn:nbn:se:umu:diva-3781 (URN)
Available from: 2004-03-12 Created: 2004-03-12Bibliographically approved
4. Structure and function of the lightharvesting complex of higher plant photosystem I
Open this publication in new window or tab >>Structure and function of the lightharvesting complex of higher plant photosystem I
Show others...
(English)Manuscript (preprint) (Other academic)
National Category
Botany
Identifiers
urn:nbn:se:umu:diva-3782 (URN)
Available from: 2004-03-12 Created: 2004-03-12 Last updated: 2015-04-29Bibliographically approved

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