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Title:Regulation of the chloroplast light harvesting antenna by plastoquinone redox: Modulation of chlorophyll metabolism and thylakoid complex organization
Author(s):Schwarz, Eliezer M.
Director of Research:Ort, Donald R.
Doctoral Committee Chair(s):Ort, Donald R.
Doctoral Committee Member(s):Huber, Steven C.; Jacobs, Thomas W.; Zielinski, Raymond E.
Department / Program:School of Integrative Biology
Degree Granting Institution:University of Illinois at Urbana-Champaign
green gel
state transitions
non-photochemical quenching
Non-Photochemical Quenching (NPQ)
psbs protein
Light Harvesting Chlorophyll a/b binding protein (LHC)
light harvesting antenna
Abstract:There is currently a great deal of interest in the possibility of modifying photosynthetic parameters to improve photosynthesis, specifically with the aim of increasing crop yields for food and biofuels. Photoinhibition, the reduction of photosynthetic electron transport in the face of excess irradiance, is thought to contribute significantly to loss of photosynthetic yield and is therefore an area of particular interest in this respect. Photoinhibition is a function of photoprotective mechanisms acting to dissipate excess absorbed light energy, and of photodamage to photosystem II due to the limitations of those mechanisms. The efficiency of photosynthetic light use, i.e., both the amount of light energy absorbed and the ability to use or dissipate it effectively, is dependent on the tailoring of the photosynthetic apparatus to the lighting environment. Such tailoring is achieved by monitoring the redox status of the plastoquionone pool, which serves as an indicator of photosynthetic electron transport. The work in this dissertation seeks to produce a better mechanistic understanding of how light intensity, as sensed by the redox state of the plastoquinone pool, signals photoprotective and acclimative responses of the light harvesting apparatus, and particularly how these responses are integrated with one another. The major proteins of the light harvesting antenna, Lhc2b and its close analogues, are suspected to be regulated at the level of protein stability by availability of pigments for protein folding. To investigate incorporation of chlorophyll into LHC protein and thylakoid complexes, a novel method was developed to enable specific metabolic radiolabeling of chlorophyll, which could be monitored by autoradiography of native green gels. This methodology was then used to probe the regulation of chlorophyll incorporation into thylakoid proteins by light intensity and plastoquione redox signaling. It was found that light availability and light intensity affect the rates of chlorophyll synthesis and incorporation into LHC as well as LHC degradation. These effects were in turn found to be dependent on reduction of the plastoquione pool. The plastoquinone redox signal was found to be mediated by both LHC phosphorylation and PsbS protonation, i.e., State Transitions and Non-Photochemical Quenching. Together, these processes suggest the importance of a conformational state of the light harvesting antenna around PSII in regulating LHC. The work presented here further advocates the importance of a conformational state at PSII to NPQ. To investigate photosystem organization in response to irradiance stress the effect of high light on thylakoid complexes was scrutinized by native green gel electrophoresis. The formation of a novel high molecular weight complex in response to high light and other changes in light intensity is described. The complex was found to be composed mainly of PSII centers and was named the Large Photocenter Complex (LPC). Both plastoquinone reduction and the PsbS protein were found to be necessary for LPC formation, though state transitions were also found to play a role in LPC kinetics. It is concluded that the LPC is part of NPQ and represents an aggregation of PSII photocenters. This conformational change is suggested to be related to the function of PsbS in regulating LHC turnover, thereby physically linking the processes of State Transitions, NPQ, and long term acclimation.
Issue Date:2011-01-14
Rights Information:Copyright 2010 Eliezer M. Schwarz
Date Available in IDEALS:2011-01-14
Date Deposited:December 2

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