Abstract
The dynamics of non-photochemical quenching (NPQ) of chlorophyll fluorescence and the dynamics of xanthophyll conversion under different actinic light conditions were studied in intact leaves of Arabidopsis thaliana. NPQ induction was investigated during up to 180 min illumination at 450, 900 and 1800 µmol photons m-2 s-1 (µE) and NPQ relaxation after 5, 30, 90 or 180 min of pre-illumination at the same light intensities. The comparison of wild-type plants with mutants affected either in xanthophyll conversion (npq1 and npq2) or PsbS expression (npq4 and L17) or lumen acidification (pgr1) indicated that NPQ states with similar, but not identical characteristics are induced at longer time range (15-60 min) in wild-type and mutant plants. In genotypes with an active xanthophyll conversion, the dynamics of two slowly (10-60 min) inducible and relaxing NPQ components were found to be kinetically correlated with zeaxanthin formation and epoxidation, respectively. However, the extent of NPQ was independent of the amount of zeaxanthin, since higher NPQ values were inducible with increasing actinic light intensities without pronounced changes in the zeaxanthin amount. These data support an indirect role of zeaxanthin in pH-independent NPQ states rather than a specific direct function of zeaxanthin as quencher in long-lasting NPQ processes. Such an indirect function might be related to an allosteric regulation of NPQ processes by zeaxanthin (e.g. through interaction of zeaxanthin at the surface of proteins) or a general photoprotective function of zeaxanthin in the lipid phase of the membrane (e.g. by modulation of the membrane fluidity or by acting as antioxidant). The found concomitant down-regulation of zeaxanthin epoxidation and recovery of photosystem II activity ensures that zeaxanthin is retained in the thylakoid membrane as long as photosystem II activity is inhibited or down-regulated. This regulation supports the view that zeaxanthin can be considered as a kind of light stress memory in chloroplasts, allowing a rapid reactivation of photoprotective NPQ processes in case of recurrent light stress periods.
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Claims 9
Claim · model-written summary
Prolonged illumination induced similar but nonidentical NPQ states in wild-type and mutant Arabidopsis.
- Taxon
- Arabidopsis
Arabidopsist0 - Outcome
- NPQ states with similar, but not identical characteristicse0
- Qualifier
- 15-60 mine0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“NPQ states with similar, but not identical characteristics are induced at longer time range (15-60 min) in wild-type and mutant plants”
t0“Arabidopsis”
Claim · model-written summary
Slowly inducible NPQ dynamics correlated kinetically with zeaxanthin formation.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- zeaxanthine0
- Outcome
- inducible and relaxing NPQ componentse0
- Qualifier
- 10-60 mine0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two slowly (10-60 min) inducible and relaxing NPQ components were found to be kinetically correlated with zeaxanthin formation and epoxidation, respectively”
t0“Arabidopsis”
Claim · model-written summary
Slowly relaxing NPQ dynamics correlated kinetically with zeaxanthin epoxidation.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- zeaxanthine0
- Outcome
- relaxing NPQ componentse0
Not reportedDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“two slowly (10-60 min) inducible and relaxing NPQ components were found to be kinetically correlated with zeaxanthin formation and epoxidation, respectively”
t0“Arabidopsis”
Claim · model-written summary
NPQ extent was independent of zeaxanthin amount.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- zeaxanthine0
- Outcome
- extent of NPQe0
- Direction
- independente0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“extent of NPQ was independent of the amount of zeaxanthin”
t0“Arabidopsis”
Claim · model-written summary
Increasing actinic light intensity induced higher NPQ without pronounced zeaxanthin amount changes.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- increasing actinic light intensitiese0
- Outcome
- NPQ valuese0
- Direction
- highere0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher NPQ values were inducible with increasing actinic light intensities without pronounced changes in the zeaxanthin amount”
t0“Arabidopsis”
Claim · model-written summary
Zeaxanthin amount showed no pronounced change as actinic light intensity increased.
- Taxon
- ArabidopsisArabidopsist0
- Treatment
- increasing actinic light intensitiese0
- Outcome
- zeaxanthin amounte0
- Direction
- without pronounced changese0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“increasing actinic light intensities without pronounced changes in the zeaxanthin amount”
t0“Arabidopsis”
Claim · model-written summary
Zeaxanthin was interpreted to have an indirect role in pH-independent NPQ states.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- zeaxanthine0
- Outcome
- pH-independent NPQ statese0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“indirect role of zeaxanthin in pH-independent NPQ states rather than a specific direct function of zeaxanthin as quencher in long-lasting NPQ processes”
t0“Arabidopsis”
Claim · model-written summary
Zeaxanthin epoxidation and photosystem II activity recovery were concomitantly down-regulated.
- Taxon
- ArabidopsisArabidopsist0
- Compound
- zeaxanthine0
- Outcome
- recovery of photosystem II activitye0
- Direction
- down-regulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“concomitant down-regulation of zeaxanthin epoxidation and recovery of photosystem II activity”
t0“Arabidopsis”
Claim · model-written summary
The coupled regulation was interpreted to retain zeaxanthin while photosystem II activity is inhibited.
- Taxon
- ArabidopsisArabidopsist0
- Outcome
- zeaxanthin is retained in the thylakoid membranee0
- Qualifier
- as long as photosystem II activity is inhibited or down-regulatede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“zeaxanthin is retained in the thylakoid membrane as long as photosystem II activity is inhibited or down-regulated”
t0“Arabidopsis”
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