FRINK Linked Data Fragments server

Matches in SemOpenAlex for { <https://semopenalex.org/work/W795837963> ?p ?o ?g. }

• W795837963 abstract "Photosynthetic organisms possess a highly efficient photo-protective apparatus respon-sible for non-photochemical quenching (NPQ) of the excess excitation energy that helps them to minimize the harmful effects of excess light. The rapidly-reversible part of NPQ, termed qE, is associated with a number of different factors: the pH gradient across the thylakoid membrane, the action of the PsbS protein, the xanthophyll cycle conversion, i.e. de-epoxidation of violaxanthin into zeaxanthin (Zx), conformational changes in the light-harvesting complexes of PS II (LHC II). The exact mechanism of qE is however not known, the quenching sites, their location and molecular origin remain questionable. These questions are addressed in the thesis by time-resolved fluorescence spectroscopy performed on different levels of organization and physiological state of the photosyn-thetic apparatus – from isolated pigment-protein complexes to intact leaves. The single photon counting technique was utilized for registering fluorescence emission with pico-seconds time resolution and exceptionally high dynamic range and signal-to-noise ratio, allowing a detailed multicomponent analysis of the fluorescence kinetics. For the first time intact plant leaves and diatom cells (Bacillariophyceae) were measured in-vivo in NPQ state in physiological conditions. The successful analysis and interpretation of the extremely complex fluorescence decay kinetics of the intact system was made possible by combining the knowledge acquired in previous studies, reviewed in the introductory part of the thesis, together with the preliminary investigations in this work, performed on isolated PS II cores, PS II enriched thylakoid membranes, and isolated LHC II in dif-ferent aggregation states. The gathered experimental data were thoroughly treated by applying a kinetic modeling (target analysis) approach in order to gain insight into the biophysical parameters (en-ergy and electron pathways, transfer and decay rate constants, species spectra that re-veal the molecular nature of the fluorescence-emitting components). Different kinetic models suitable for each particular experimental system were designed and applied to fit the data. In addition, in some instances theoretical modeling was applied, which re-veals the contributions of the various intermediates to specific apparent lifetimes and al-lows to estimate the time dependence of the populations of the inter¬mediates. Considerable similarities in the early electron transfer rates of PS II reaction centres (RCs, without antenna), cyanobacterial PS II cores (with core antenna), and a higher plant PS II enriched membranes (with core and peripheral antenna) were found. The energy transfer rates scale with increase in the antenna size. Thus the dynamics of the initial photochemical steps of PS II could be implemented in the model describing the in-vivo fluorescence as well. Fluorescence time-resolved kinetics was measured in vivo from leaves of Arabidopsis in unquenched dark-adapted states with open and closed RCs (F0 and Fmax, respectively) and compared to the kinetics measured under quenched light-adapted condition (FNPQ). The data were fit using a kinetic compartment model combining the previously investi-gated energy and electron transfer dynamics in PS II and PS I. The results of the kinetic modeling revealed two principal changes in the fluorescence kinetics, signifying the gen-eration of NPQ: 1) appearance of a new far-red-enhanced fluorescence component func-tionally disconnected from either PS I or PS II and that was shown to originate from peripheral LHC II detached from PS II; 2) increase of the non-photochemical deactiva-tion rate (kD) that is a direct measure of NPQ in the PS II-attached antenna. Thus, NPQ was found to consist of two separate mechanisms and sites of action, termed quenching site 1 and 2 (Q1 and Q2), respectively. These two quenching sites were further investi-gated by analyzing the fluorescence kinetics in different Arabidopsis mutants lacking dif-ferent components of the photosynthetic apparatus and also by comparison with isolated LHC II in vitro. The spectral features of the fluorescence of disconnected LHC II were reminiscent of the fluorescence of LHC II oligomers in vitro, therefore it was proposed that the Q1 site of quenching represents detached and oligomerized LHC II. Thus the NPQ-associated addi-tional fluorescence component serves as a spectroscopic marker for the formation of LHC II oligomers in vivo. It is characterized by a spectrally broad and a strongly far-red enhanced fluorescence spectrum. The far-red emitting state is proposed to be an emis-sive Chl-Chl charge transfer state. The Q1 site of quenching was missing in the Arabidop-sis mutant npq4 lacking PsbS protein but was enhanced in the PsbS overexpressing mutant (L17), therefore it was concluded that the role of PsbS in NPQ is to mediate the detachment and oligomerization of LHC II. The increase of the kD constant was not observed in the Arabidopsis mutant npq1 lacking Zx but was present in both npq4 and L17. Therefore the Q2 site is strictly dependent on Zx availability and does not depend on the action of PsbS. A study of minor antenna knock-out mutants – koCP24, koCP26 and koCP24/koCP26 revealed further details of the Q2 mechanism – CP24 is the most crucial minor antenna complex for the Q2 quench-ing, whereas CP26 does not take part in it. In conclusion of the results obtained from the time-resolved fluorescence analysis of in-tact leaves, a new model of the qE mechanism in higher plants was developed. It de-scribes the location and molecular origin of the two quenching sites that work independently and complement each other. The research work on NPQ was extended to cover diatoms that represent a major part of the phytoplankton. We aimed to find differences in the NPQ mechanism in diatoms since they have a different structure of the thylakoid membrane, and completely different an-tenna compared to higher plants. Surprisingly, despite of the differences, the diatoms Phaeodactylum tricornutum and Cyclotella meneghiniana operated the same qE mecha-nism with the same two quenching sites. As a result of the analysis of the diatom fluores-cence kinetics under quenched and unquenched conditions, a model for the NPQ in diatoms was presented. According to this model there are two subpopulations of the light-harvesting antenna (fucoxanthin-chlorophyll-binding protein, FCP). The Q1 site of quenching is located in FCP subpopulation II which is detached from PS II and oligomer-ized under high light intensities. The Q2 site takes place in FCP subpopulation I, which is attached to PS II. Regardless of what type of antenna the photosynthetic organisms pos-sess, they seem to utilize the same NPQ mechanisms which turn out to have universal character." @default.
• W795837963 created "2016-06-24" @default.
• W795837963 creator A5004144928 @default.
• W795837963 date "2009-01-01" @default.
• W795837963 modified "2023-09-26" @default.
• W795837963 title "On the mechanisms of non-photochemical quenching in plants and diatoms" @default.
• W795837963 hasPublicationYear "2009" @default.
• W795837963 type Work @default.
• W795837963 sameAs 795837963 @default.
• W795837963 citedByCount "0" @default.
• W795837963 crossrefType "dissertation" @default.
• W795837963 hasAuthorship W795837963A5004144928 @default.
• W795837963 hasConcept C120665830 @default.
• W795837963 hasConcept C121332964 @default.
• W795837963 hasConcept C121745418 @default.
• W795837963 hasConcept C185592680 @default.
• W795837963 hasConcept C39432304 @default.
• W795837963 hasConcept C75473681 @default.
• W795837963 hasConcept C87355193 @default.
• W795837963 hasConcept C91881484 @default.
• W795837963 hasConceptScore W795837963C120665830 @default.
• W795837963 hasConceptScore W795837963C121332964 @default.
• W795837963 hasConceptScore W795837963C121745418 @default.
• W795837963 hasConceptScore W795837963C185592680 @default.
• W795837963 hasConceptScore W795837963C39432304 @default.
• W795837963 hasConceptScore W795837963C75473681 @default.
• W795837963 hasConceptScore W795837963C87355193 @default.
• W795837963 hasConceptScore W795837963C91881484 @default.
• W795837963 hasLocation W7958379631 @default.
• W795837963 hasOpenAccess W795837963 @default.
• W795837963 hasPrimaryLocation W7958379631 @default.
• W795837963 hasRelatedWork W1977920831 @default.
• W795837963 hasRelatedWork W1983505732 @default.
• W795837963 hasRelatedWork W1993302990 @default.
• W795837963 hasRelatedWork W1998023605 @default.
• W795837963 hasRelatedWork W2003546568 @default.
• W795837963 hasRelatedWork W2006357804 @default.
• W795837963 hasRelatedWork W2023274452 @default.
• W795837963 hasRelatedWork W2030114678 @default.
• W795837963 hasRelatedWork W2031482332 @default.
• W795837963 hasRelatedWork W2040171571 @default.
• W795837963 hasRelatedWork W2062355152 @default.
• W795837963 hasRelatedWork W2062626113 @default.
• W795837963 hasRelatedWork W2071688446 @default.
• W795837963 hasRelatedWork W2132135000 @default.
• W795837963 hasRelatedWork W2188888703 @default.
• W795837963 hasRelatedWork W2316397420 @default.
• W795837963 hasRelatedWork W2612839773 @default.
• W795837963 hasRelatedWork W2741508336 @default.
• W795837963 hasRelatedWork W368000648 @default.
• W795837963 hasRelatedWork W3214322829 @default.
• W795837963 isParatext "false" @default.
• W795837963 isRetracted "false" @default.
• W795837963 magId "795837963" @default.
• W795837963 workType "dissertation" @default.