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State transition in Arabidopsis thaliana and Chlamydomonas reinhardtii

Roest, G.A.B. (2010) State transition in Arabidopsis thaliana and Chlamydomonas reinhardtii. Bachelor's Thesis, Biology.

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Photosynthesis is the process by which plants and green algae store light energy in the form of ATP and NADPH and use this to fixate CO2. It demands an efficient cooperation between PSII and PSI, since electrons generated by photosystem II are transported to photosystem I via a plastoquinone pool and cytochrome b6f. The efficiency of electron transport is at stake when light conditions change, since photosystem I and photosystem II do not absorb light with the same wavelength. State transitions, the migration of a mobile LHCII pool between PSI and PSII, make sure that under conditions where photosystem I and photosystem II are differentially excited the cooperation still is as efficient as possible. In plants state transitions seem to function to balance the energy absorption by PSI and PSII, while in green algae it is a switch between linear and cyclic electron flow around PSI, and thus a way to regulate the ATP production. The redox state of the plastoquinone pool is the determinant for state transition. Arabidopsis thaliana serves as a model organism for state transition in plants. In green algae Chlamydomonas reinhardtii fulfils this role. In A. thaliana about 15-20% of the total amount of LHCII serves as a mobile pool, while in C. reinhardtii it is as much as 80%. In A. thaliana the migrating part is the M-trimer, and especially Lhcb3 is proposed to have an important role. Phosphorylation of LHCII by STN7 induces the transition from PSII to PSI. STN8, which phosphorylates the PSII core, is also important. PPH1 dephosphorylates LHCII, and is thus responsible for the state 2 to state 1 transition. In C. reinhardtii the migrating subunits are CP26, CP29 and LhcbM5. Phosphorylation of the residues Thr17 and Ser103 of CP29 by Stt7 seems to induce the transition. Also CP26 and the core subunits CP43 and D2 are phosphorylated upon state 1 to state 2 transition. Phosphorylation is proposed to lead to the dissociation of PSII megacomplexes into supercomplexes, and additionally to the migration of the LHCII subunits.

Item Type: Thesis (Bachelor's Thesis)
Degree programme: Biology
Thesis type: Bachelor's Thesis
Language: English
Date Deposited: 15 Feb 2018 07:44
Last Modified: 15 Feb 2018 07:44

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