Kovács L, Damkjaer J, Kereïche S, Ilioaia C, Ruban AV, Boekema EJ, Jansson S, Horton P
Lack of the light-harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts
Plant Cell 2006 18:3106-3120
The photosystem II (PSII) light-harvesting antenna in higherplants contains a number of highly conserved gene products whosefunction is unknown. Arabidopsis thaliana plants depleted ofone of these, the CP24 light-harvesting complex, have been analyzed.CP24-deficient plants showed a decrease in light-limited photosyntheticrate and growth, but the pigment and protein content of thethylakoid membranes were otherwise almost unchanged. However,there was a major change in the macroorganization of PSII withinthese membranes; electron microscopy and image analysis revealedthe complete absence of the C2S2M2 light-harvesting complexII (LHCII)/PSII supercomplex predominant in wild-type plants.Instead, only C2S2 supercomplexes, which are deficient in theLHCIIb M-trimers, were found. Spectroscopic analysis confirmedthe disruption of the wild-type macroorganization of PSII. Itwas found that the functions of the PSII antenna were disturbed:connectivity between PSII centers was reduced, and maximum photochemicalyield was lowered; rapidly reversible nonphotochemical quenchingwas inhibited; and the state transitions were altered kinetically.CP24 is therefore an important factor in determining the structureand function of the PSII light-harvesting antenna, providingthe linker for association of the M-trimer into the PSII complex,allowing a specific macroorganization that is necessary bothfor maximum quantum efficiency and for photoprotective dissipationof excess excitation energy.
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