This article is cited by 38 publications. Purification of PSI–LHCI complexes (Figure S1), characterization of PSI–LHCI complexes purified from WT and mutant genotypes (Figure S2), fluorescence-detected magnetic resonance of the chlorophyll and carotenoid triplet states on PSI–LHCI complexes isolated from dark-adapted, WT plants (Figure S3), reconstruction of the FDMR spectra of the 3Chl* states on purified PSI–LHCI complexes, with Gaussian components (Figure S4), fluorescence-detected magnetic resonance of 3Car* and 3Chl* on purified PSI–LHCI complexes (Figure S5), purification of PSI core and LHCI complexes (Figure S6), parameters of the Global Gaussian Deconvolution of 3Chl* states on purified PSI–LHCI complexes, with Gaussians components (Table 1S), and amplitude of the Gaussian components of 3Chl* states used in the reconstruction of the FDMR spectra on purified PSI–LHCI complexes at different wavelengths (Table 2S) ( PDF)
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The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.biochem.6b00425. We conclude that PSI–LHCI complex-bound β-carotene elicits a protective response, consisting of a reduction in the yield of harmful triplet excited states, while accumulation of zeaxanthin plays a minor role in restoring phototolerance. When PSI was fractioned into its functional moieties, it was revealed that the boost in the rate of singlet oxygen release caused by β-carotene depletion was greater in LHCI than in the core complex. Accordingly, fluorescence-detected magnetic resonance analysis showed an increase in the amplitude of signals assigned to chlorophyll triplets in β-carotene-depleted complexes. The PSI–LHCI complex purified from szl1 was more photosensitive than the corresponding wild-type and npq1 complexes, as is evident from its faster photobleaching and increased rate of singlet oxygen release, suggesting that β-carotene is crucial in controlling chlorophyll triplet formation. When exposed to excess light, the szl1 genotype displayed PSI photoinhibition stronger than that of wild-type plants, while removing zeaxanthin had no such effect.
We functionally dissected various components of the xanthophyll- and carotene-dependent photoprotection mechanism of PSI by analyzing two Arabidopsis mutants: szl1 plants, with a carotene content lower than that of the wild type, and npq1, with suppressed zeaxanthin formation. β-Carotene is present in both the core complexes and light-harvesting system (LHCI) of Photosystem (PS) I, while xanthophylls lutein and violaxanthin bind exclusively to its antenna moiety another xanthophyll, zeaxanthin, which protects chloroplasts against photooxidative damage, binds to the LHCI complexes under conditions of excess light.
Carotenes and their oxygenated derivatives, xanthophylls, are structural elements of the photosynthetic apparatus and contribute to increasing both the light-harvesting and photoprotective capacity of the photosystems.
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