Lack of the light-harvesting complex CP24 affects the structure and function of the grana membranes of higher plant chloroplasts.

• 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.

Nyckelord

Arabidopsis/*metabolism/radiation effects/ultrastructure

Arabidopsis Proteins/analysis/isolation & purification/*metabolism

Chloroplasts/*ultrastructure

Chromatography; Gel

Circular Dichroism

DNA; Bacterial/metabolism

Fluorescence

Light

Light-Harvesting Protein Complexes/analysis/*deficiency/isolation & purification

Models; Biological

Mutagenesis; Insertional

Photosynthesis/radiation effects

Photosynthetic Reaction Center Complex Proteins/metabolism

Photosystem II Protein Complex/metabolism

Pigments; Biological/metabolism

Plant Leaves/radiation effects

RNA; Antisense/metabolism

Structure-Activity Relationship

Temperature

Thylakoids/*ultrastructure

Publikations- och innehållstyp

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