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Dissecting the photosystem II light-harvesting antenna
Umeå University, Faculty of Science and Technology, Department of Plant Physiology.
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In photosynthesis, sunlight is converted into chemical energy that is stored mainly as carbohydrates and supplies basically all life on Earth with energy.

In order to efficiently absorb the light energy, plants have developed the outer light harvesting antenna, which is composed of ten different protein subunits (LHC) that bind chlorophyll a and b as well as different carotenoids. In addition to the light harvesting function, the antenna has the capacity to dissipate excess energy as heat (feedback de-excitation or qE), which is crucial to avoid oxidative damage under conditions of high excitation pressure. Another regulatory function in the antenna is the state transitions in which the distribution of the trimeric LHC II between photosystem I (PS I) and II is controlled. The same ten antenna proteins are conserved in all higher plants and based on evolutionary arguments this has led to the suggestion that each protein has a specific function.

I have investigated the functions of individual antenna proteins of PS II (Lhcb proteins) by antisense inhibition in the model plant Arabidopsis thaliana. Four antisense lines were obtained, in which the target proteins were reduced, in some cases beyond detection level, in other cases small amounts remained.

The results show that CP29 has a unique function as organising the antenna. CP26 can form trimers that substitute for Lhcb1 and Lhcb2 in the antenna structure, but the trimers that accumulate as a response to the lack of Lhcb1 and Lhcb2 cannot take over the LHC II function in state transitions. It has been argued that LHC II is essential for grana stacking, but antisense plants without Lhcb1 and Lhcb2 do form grana. Furthermore, LHC II is necessary to maintain growth rates in very low light.

Numerous biochemical evidences have suggested that CP29 and/or CP26 were crucial for feedback de-excitation. Analysis of two antisense lines each lacking one of these proteins clearly shows that there is no direct involvement of either CP29 or CP26 in this process. Investigation of the other antisense lines shows that no Lhcb protein is indispensable for qE. A model for feedback de-excitation is presented in which PsbS plays a major role.

The positions of the minor antenna proteins in the PS II supercomplex were established by comparisons of transmission electron micrographs of supercomplexes from the wild type and antisense plants.

A fitness experiment was conducted where the antisense plants were grown in the field and seed production was used to estimate the fitness of the different genotypes. Based on the results from this experiment it is concluded that each Lhcb protein is important, because all antisense lines show reduced fitness in the field.

Place, publisher, year, edition, pages
Umeå: Fysiologisk botanik , 2003. , 59 p.
Keyword [en]
Plant physiology, antisense, Arabidopsis thaliana, chlorophyll, carotenoid, feedback de-excitation, fitness, LHC, NPQ, photosynthesis, state transitions, xanthophyll
Keyword [sv]
Växtfysiologi
National Category
Botany
Research subject
Physiological Botany
Identifiers
URN: urn:nbn:se:umu:diva-25ISBN: 91-7305-387-2 (print)OAI: oai:DiVA.org:umu-25DiVA: diva2:142816
Public defence
2003-02-28, Umeå, 10:00
Available from: 2003-02-28 Created: 2003-02-28 Last updated: 2012-08-08Bibliographically approved
List of papers
1. Antisense inhibition of the photosynthetic antenna proteins CP29 and CP26: implications for the mechanism of protective energy dissipation
Open this publication in new window or tab >>Antisense inhibition of the photosynthetic antenna proteins CP29 and CP26: implications for the mechanism of protective energy dissipation
2001 (English)In: The Plant Cell, ISSN 1040-4651, E-ISSN 1532-298X, Vol. 13, no 5, 1193-1204 p.Article in journal (Refereed) Published
Abstract [en]

The specific roles of the chlorophyll a/b binding proteins CP29 and CP26 in light harvesting and energy dissipation within the photosynthetic apparatus have been investigated. Arabidopsis was transformed with antisense constructs against the genes encoding the CP29 or CP26 apoprotein, which gave rise to several transgenic lines with remarkably low amounts of the antisense target proteins. The decrease in the level of CP24 protein in the CP29 antisense lines indicates a physical interaction between these complexes. Analysis of chlorophyll fluorescence showed that removal of the proteins affected photosystem II function, probably as a result of changes in the organization of the light-harvesting antenna. However, whole plant measurements showed that overall photosynthetic rates were similar to those in the wild type. Both antisense lines were capable of the qE type of nonphotochemical fluorescence quenching, although there were minor changes in the capacity for quenching and in its induction kinetics. High-light-induced violaxanthin deepoxidation to zeaxanthin was not affected, although the pool size of these pigments was decreased slightly. We conclude that CP29 and CP26 are unlikely to be sites for nonphotochemical quenching.

Place, publisher, year, edition, pages
American Society of Plant Biologists, 2001
Research subject
Physiological Botany
Identifiers
urn:nbn:se:umu:diva-3907 (URN)10.1105/tpc.13.5.1193 (DOI)000169030000017 ()
Available from: 2003-02-28 Created: 2003-02-28 Last updated: 2017-12-14Bibliographically approved
2. The structure of photosystem II in Arabidopsis: localization of the CP26 and CP29 antenna complexes
Open this publication in new window or tab >>The structure of photosystem II in Arabidopsis: localization of the CP26 and CP29 antenna complexes
Show others...
2003 (English)In: Biochemistry, ISSN 0006-2960, E-ISSN 1520-4995, Vol. 42, no 3, 608-613 p.Article in journal (Refereed) Published
Abstract [en]

A genetic approach has been adopted to investigate the organization of the light-harvesting proteins in the photosystem II (PSII) complex in plants. PSII membrane fragments were prepared from wild-type Arabidopis thaliana and plants expressing antisense constructs to Lhcb4 and Lhcb5 genes, lacking CP29 and CP26, respectively (Andersson et al. (2001) Plant Cell 13, 1193-1204). Ordered PSII arrays and PSII supercomplexes were isolated from the membranes of plants lacking CP26 but could not be prepared from those lacking CP29. Membranes and supercomplexes lacking CP26 were less stable than those prepared from the wild type. Transmission electron microscopy aided by single-particle image analysis was applied to the ordered arrays and the isolated PSII complexes. The difference between the images obtained from wild type and antisense plants showed the location of CP26 to be near CP43 and one of the light-harvesting complex trimers. Therefore, the location of the CP26 within PSII was directly established for the first time, and the location of the CP29 complex was determined by elimination. Alterations in the packing of the PSII complexes in the thylakoid membrane also resulted from the absence of CP26. The minor light-harvesting complexes each have a unique location and important roles in the stabilization of the oligomeric PSII structure.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2003
National Category
Biochemistry and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-3908 (URN)10.1021/bi027109z (DOI)000180568900002 ()
Available from: 2003-02-28 Created: 2003-02-28 Last updated: 2017-12-14Bibliographically approved
3. Absence of the main light-harvesting complex of photosystem II affects photosynthetic function.
Open this publication in new window or tab >>Absence of the main light-harvesting complex of photosystem II affects photosynthetic function.
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In: Plant journal, Vol. 2003Article in journal (Refereed) Accepted
Identifiers
urn:nbn:se:umu:diva-3909 (URN)
Available from: 2003-02-28 Created: 2003-02-28Bibliographically approved
4. Plants lacking the main light harvesting complex retain photosystem II macro-organization
Open this publication in new window or tab >>Plants lacking the main light harvesting complex retain photosystem II macro-organization
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2003 (English)In: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 421, 648-652 p.Article in journal (Refereed) Published
Place, publisher, year, edition, pages
Nature Publishing Group, 2003
National Category
Biological Sciences
Identifiers
urn:nbn:se:umu:diva-3910 (URN)10.1038/nature01344 (DOI)
Available from: 2003-02-28 Created: 2003-02-28 Last updated: 2017-12-14Bibliographically approved
5. Loss of Lhcb1 and Lhcb2 decreases growth in extreme low light.
Open this publication in new window or tab >>Loss of Lhcb1 and Lhcb2 decreases growth in extreme low light.
Manuscript (Other academic)
Identifiers
urn:nbn:se:umu:diva-3911 (URN)
Available from: 2003-02-28 Created: 2003-02-28 Last updated: 2010-01-13Bibliographically approved

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