| 1. |
- Damkjaer, Jakob, 1976-
(author)
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Phosphorylation in State Transition : Less cause more effect
- 2011
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Doctoral thesis (other academic/artistic)abstract
- Study of the Arabidopsis thaliana knockout mutant lacking Lhcb3 (koLhcb3) have revealed a close similarity to the wild type plants. Growth rate, NPQ, qP, Φ(PSII), circular dichroism spectra, pigment composition and content of LCHII trimers have been found to be unaffected by this mutation. The proteomic analysis shows only some minor increases in the amount of Lhcb1 and Lhcb2. PAM fluorometry revealed a significant increase in the rate of the state 1 to state 2 state transition in the koLhcb3. None the less, the extent of state transition is identical to wild type. Alterations in the PSII-LHCII supercomplex structure have been demonstrated as well. The M-trimer was found to be rotated ~21° CCW. This altered binding of the LHCII M-trimer is likely the cause of the altered affinity resulting in the increased rate of state transition. Proteomic analysis of the phosphorylation of LHCII revealed a significant increase in state 1 and 2 LHCII phosphorylation relative to wild type. Investigation whether phosphorylation or the altered LHCII binding is the cause of the accelerated rate of state transition have not been conclusive so far. A Lhcb6 depleted mutant (koLhcb6) showed a significant alteration of the PSII-LHCII supercomplex structure and photosynthetic acclimation processes. The LHCII M-trimer is depleted in the PSII-LHCII supercomplexes causing the state transition process to be “stuck” in state 2 and the mutants ability to preform NPQ is inhibited as well. The Lhcb6 protein was concluded to be essential for the binding of the LHCII M-trimer to the PSII core as well as energy transfer. The depletion of LHCII M-trimer was linked to the reduced ability to photoacclimate using NPQ as well.
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| 2. |
- Damkjær, Jakob T, 1976-, et al.
(author)
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The photosystem II light-harvesting protein Lhcb3 affects the macrostructure of photosystem II and the rate of state transitions in Arabidopsis
- 2009
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 21, s. 3245-3256
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Journal article (peer-reviewed)abstract
- The main trimeric light-harvesting complex of higher plants (LHCII) consists of three different Lhcb proteins (Lhcb1-3). We show that Arabidopsis thaliana T-DNA knockout plants lacking Lhcb3 (koLhcb3) compensate for the lack of Lhcb3 by producing increased amounts of Lhcb1 and Lhcb2. As in wild-type plants, LHCII-photosystem II (PSII) supercomplexes were present in Lhcb3 knockout plants (koLhcb3), and preservation of the LHCII trimers (M trimers) indicates that the Lhcb3 in M trimers has been replaced by Lhcb1 and/or Lhcb2. However, the rotational position of the M LHCII trimer was altered, suggesting that the Lhcb3 subunit affects the macrostructural arrangement of the LHCII antenna. The absence of Lhcb3 did not result in any significant alteration in PSII efficiency or qE type of nonphotochemical quenching, but the rate of transition from State 1 to State 2 was increased in koLhcb3, although the final extent of state transition was unchanged. The level of phosphorylation of LHCII was increased in the koLhcb3 plants compared with wild-type plants in both State 1 and State 2. The relative increase in phosphorylation upon transition from State 1 to State 2 was also significantly higher in koLhcb3. It is suggested that the main function of Lhcb3 is to modulate the rate of state transitions.
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| 3. |
- Kovács, Laszlo, et al.
(author)
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Lack of the light-harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts.
- 2006
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In: The Plant Cell. - : Oxford University Press (OUP). - 1040-4651 .- 1532-298X. ; 18:11, s. 3106-20
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Journal article (peer-reviewed)abstract
- The photosystem II (PSII) light-harvesting antenna in higher plants contains a number of highly conserved gene products whose function is unknown. Arabidopsis thaliana plants depleted of one of these, the CP24 light-harvesting complex, have been analyzed. CP24-deficient plants showed a decrease in light-limited photosynthetic rate and growth, but the pigment and protein content of the thylakoid membranes were otherwise almost unchanged. However, there was a major change in the macroorganization of PSII within these membranes; electron microscopy and image analysis revealed the complete absence of the C2S2M2 light-harvesting complex II (LHCII)/PSII supercomplex predominant in wild-type plants. Instead, only C2S2 supercomplexes, which are deficient in the LHCIIb M-trimers, were found. Spectroscopic analysis confirmed the disruption of the wild-type macroorganization of PSII. It was found that the functions of the PSII antenna were disturbed: connectivity between PSII centers was reduced, and maximum photochemical yield was lowered; rapidly reversible nonphotochemical quenching was inhibited; and the state transitions were altered kinetically. CP24 is therefore an important factor in determining the structure and function of the PSII light-harvesting antenna, providing the linker for association of the M-trimer into the PSII complex, allowing a specific macroorganization that is necessary both for maximum quantum efficiency and for photoprotective dissipation of excess excitation energy.
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