Non-photochemical Dotaz Zobrazit nápovědu
Diatoms are especially important microorganisms because they constitute the larger group of microalgae. To survive the constant variations of the light environment, diatoms have developed mechanisms aiming at the dissipation of excess energy, such as the xanthophyll cycle and the non-photochemical chlorophyll (Chl) fluorescence quenching. This contribution is dedicated to the relaxation of the latter process when the adverse conditions cease. An original nonlinear regression analysis of the relaxation of non-photochemical Chl fluorescence quenching, qN, in diatoms is presented. It was used to obtain experimental evidence for the existence of three time-resolved components in the diatom Phaeodactylum tricornutum: qNf, qNi and qNs. qNf (s time-scale) and qNs (h time-scale) are exponential in shape. By contrast, qNi (min time-scale) is of sigmoidal nature and is dominant among the three components. The application of metabolic inhibitors (dithiothreitol, ammonium chloride, cadmium and diphenyleneiodonium chloride) allowed the identification of the mechanisms on which each component mostly relies. qNi is linked to the relaxation of the ΔpH gradient and the reversal of the xanthophyll cycle. qNs quantifies the stage of photoinhibition caused by the high light exposure, qNf seems to reflect fast conformational changes within thylakoid membranes in the vicinity of the photosystem II complexes.
- MeSH
- časové faktory MeSH
- chlorid amonný MeSH
- chlorofyl metabolismus účinky záření MeSH
- dithiothreitol MeSH
- fluorescence MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- kadmium MeSH
- kinetika MeSH
- oniové sloučeniny MeSH
- regresní analýza MeSH
- rozsivky fyziologie MeSH
- světlo * MeSH
- tylakoidy metabolismus MeSH
- xanthofyly metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Photosynthesis uses light as a source of energy but its excess can result in production of harmful oxygen radicals. To avoid any resulting damage, phototrophic organisms can employ a process known as non-photochemical quenching (NPQ), where excess light energy is safely dissipated as heat. The mechanism(s) of NPQ vary among different phototrophs. Here, we describe a new type of NPQ in the organism Rhodomonas salina, an alga belonging to the cryptophytes, part of the chromalveolate supergroup. Cryptophytes are exceptional among photosynthetic chromalveolates as they use both chlorophyll a/c proteins and phycobiliproteins for light harvesting. All our data demonstrates that NPQ in cryptophytes differs significantly from other chromalveolates - e.g. diatoms and it is also unique in comparison to NPQ in green algae and in higher plants: (1) there is no light induced xanthophyll cycle; (2) NPQ resembles the fast and flexible energetic quenching (qE) of higher plants, including its fast recovery; (3) a direct antennae protonation is involved in NPQ, similar to that found in higher plants. Further, fluorescence spectroscopy and biochemical characterization of isolated photosynthetic complexes suggest that NPQ in R. salina occurs in the chlorophyll a/c antennae but not in phycobiliproteins. All these results demonstrate that NPQ in cryptophytes represents a novel class of effective and flexible non-photochemical quenching.
- MeSH
- buněčná membrána metabolismus účinky záření MeSH
- Cryptophyta cytologie enzymologie metabolismus účinky záření MeSH
- fotosystém II - proteinový komplex metabolismus MeSH
- kinetika MeSH
- koncentrace vodíkových iontů MeSH
- kvarterní struktura proteinů MeSH
- multimerizace proteinu účinky záření MeSH
- proteiny vázající chlorofyl chemie metabolismus MeSH
- protony MeSH
- substrátová specifita MeSH
- světlo škodlivé účinky MeSH
- xanthofyly metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Non-photochemical quenching (NPQ) is a mechanism protecting photosynthetic organisms against excessive irradiation. Here, we analyze a unique NPQ mechanism in the alga Chromera velia, a recently discovered close relative of apicomplexan parasites. NPQ in C. velia is enabled by an operative and fast violaxanthin de-epoxidation to zeaxanthin without accumulation of antheraxanthin. In C. velia violaxanthin also serves as a main light-harvesting pigment. Therefore, in C. velia violaxanthin acts as a key factor in both light harvesting and photoprotection. This is in contrast to a similar alga, Nannochloropsis limnetica, where violaxanthin has only light-harvesting function.
A new method of the chlorophyll (Chl) a fluorescence quenching analysis is described, which allows the calculation of values of (at least) three components of the non-photochemical quenching of the variable Chl a fluorescence (q (N)) using a non-linear regression of a multi-exponential function within experimental data. Formulae for coefficients of the "energy"-dependent (DeltapH-dependent) quenching (q (E)), the state-transition quenching (q (T)) and the photo/inhibitory quenching (q (I)) of Chl a fluorescence were found on the basis of three assumptions: (i) the dark relaxation kinetics of q (N), as well as of all its components, is of an exponential nature, (ii) the superposition principle is valid for individual Chl a fluorescence quenching processes and (iii) the same reference fluorescence level (namely the maximum variable Chl a fluorescence yield in the dark-adapted state, F (V)) is used to define both q (N) and its components. All definitions as well as the algorithms for analytical recognition of the q (N) components are theoretically clarified and experimentally tested. The described theory results in a rather simple equation allowing to compute values for all q (N) components (q (E), q (T), q (I)) as well as the half-times of relaxation (tau(1/2)) of corresponding quenching processes. It is demonstrated that under the above assumptions it holds: q (N) = q (E) + q (T) + q (I). The theoretically derived equations are tested, and the results obtained are discussed for non-stressed and stressed photosynthetically active samples. Semi-empirical formulae for a fast estimation of values of the q (N) components from experimental data are also given.
We explored photoprotective strategies in a cryptophyte alga Rhodomonas salina. This cryptophytic alga represents phototrophs where chlorophyll a/c antennas in thylakoids are combined with additional light-harvesting system formed by phycobiliproteins in the chloroplast lumen. The fastest response to excessive irradiation is induction of non-photochemical quenching (NPQ). The maximal NPQ appears already after 20 s of excessive irradiation. This initial phase of NPQ is sensitive to Ca2+ channel inhibitor (diltiazem) and disappears, also, in the presence of non-actin, an ionophore for monovalent cations. The prolonged exposure to high light of R. salina cells causes photoinhibition of photosystem II (PSII) that can be further enhanced when Ca2+ fluxes are inhibited by diltiazem. The light-induced reduction in PSII photochemical activity is smaller when compared with immotile diatom Phaeodactylum tricornutum. We explain this as a result of their different photoprotective strategies. Besides the protective role of NPQ, the motile R. salina also minimizes high light exposure by increased cell velocity by almost 25% percent (25% from 82 to 104 μm/s). We suggest that motility of algal cells might have a photoprotective role at high light because algal cell rotation around longitudinal axes changes continual irradiation to periodically fluctuating light.
Life on Earth depends on photosynthesis, the conversion of light energy into chemical energy. Plants collect photons by light harvesting complexes (LHC)-abundant membrane proteins containing chlorophyll and xanthophyll molecules. LHC-like proteins are similar in their amino acid sequence to true LHC antennae, however, they rather serve a photoprotective function. Whether the LHC-like proteins bind pigments has remained unclear. Here, we characterize plant LHC-like proteins (LIL3 and ELIP2) produced in the cyanobacterium Synechocystis sp. PCC 6803 (hereafter Synechocystis). Both proteins were associated with chlorophyll a (Chl) and zeaxanthin and LIL3 was shown to be capable of quenching Chl fluorescence via direct energy transfer from the Chl Qy state to zeaxanthin S1 state. Interestingly, the ability of the ELIP2 protein to quench can be acquired by modifying its N-terminal sequence. By employing Synechocystis carotenoid mutants and site-directed mutagenesis we demonstrate that, although LIL3 does not need pigments for folding, pigments stabilize the LIL3 dimer.
- MeSH
- chlorofyl metabolismus MeSH
- karotenoidy metabolismus MeSH
- multimerizace proteinu MeSH
- mutace MeSH
- přenos energie MeSH
- proteiny chloroplastové chemie genetika metabolismus MeSH
- proteiny huseníčku chemie genetika metabolismus MeSH
- sbalování proteinů MeSH
- Synechocystis genetika metabolismus MeSH
- vazba proteinů MeSH
- xanthofyly metabolismus MeSH
- zeaxanthiny genetika metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Chl synthase (ChlG) is an important enzyme of the Chl biosynthetic pathway catalyzing attachment of phytol/geranylgeraniol tail to the chlorophyllide molecule. Here we have investigated the Flag-tagged ChlG (f.ChlG) in a complex with two different high-light inducible proteins (Hlips) HliD and HliC. The f.ChlG-Hlips complex binds a Chl a and three different carotenoids, β-carotene, zeaxanthin and myxoxanthophyll. Application of ultrafast time-resolved absorption spectroscopy performed at room and cryogenic temperatures revealed excited-state dynamics of complex-bound pigments. After excitation of Chl a in the complex, excited Chl a is efficiently quenched by a nearby carotenoid molecule via energy transfer from the Chl a Qy state to the carotenoid S1 state. The kinetic analysis of the spectroscopic data revealed that quenching occurs with a time constant of ~2ps and its efficiency is temperature independent. Even though due to its long conjugation myxoxanthophyll appears to be energetically best suited for role of Chl a quencher, based on comparative analysis and spectroscopic data we propose that β-carotene bound to Hlips acts as the quencher rather than myxoxanthophyll and zeaxanthin, which are bound at the f.ChlG and Hlips interface. The S1 state lifetime of the quencher has been determined to be 13ps at room temperature and 21ps at 77K. These results demonstrate that Hlips act as a conserved functional module that prevents photodamage of protein complexes during photosystem assembly or Chl biosynthesis.
- MeSH
- bakteriální proteiny chemie MeSH
- fotolýza MeSH
- karotenoidy farmakologie MeSH
- ligasy tvořící vazby C-O chemie MeSH
- sinice enzymologie MeSH
- světlosběrné proteinové komplexy chemie MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
Drug investigation, ISSN 0114-2402 Supplement Vol. 3. 2
94 s. : grafy, tab. ; 25 cm
- MeSH
- antiflogistika nesteroidní MeSH
- histamin MeSH
- oxidancia fotochemická MeSH
- prostaglandiny MeSH
- zánět farmakoterapie MeSH
- Publikační typ
- kongresy MeSH
- Konspekt
- Farmacie. Farmakologie
- NLK Obory
- farmacie a farmakologie
Although it is well known that chromosomes are non-randomly organized during interphase, it is not completely clear whether higher-order chromatin structure is transmitted from mother to daughter cells. Therefore, we addressed the question of how chromatin is rearranged during interphase and whether heterochromatin pattern is transmitted after mitosis. We additionally tested the similarity of chromatin arrangement in sister interphase nuclei. We noticed a very active cell rotation during interphase, especially when histone hyperacetylation was induced or transcription was inhibited. This natural phenomenon can influence the analysis of nuclear arrangement. Using photoconversion of Dendra2-tagged core histone H4 we showed that the distribution of chromatin in daughter interphase nuclei differed from that in mother cells. Similarly, the nuclear distribution of heterochromatin protein 1β (HP1β) was not completely identical in mother and daughter cells. However, identity between mother and daughter cells was in many cases evidenced by nucleolar composition. Moreover, morphology of nucleoli, HP1β protein, Cajal bodies, chromosome territories, and gene transcripts were identical in sister cell nuclei. We conclude that the arrangement of interphase chromatin is not transmitted through mitosis, but the nuclear pattern is identical in naturally synchronized sister cells. It is also necessary to take into account the possibility that cell rotation and the degree of chromatin condensation during functionally specific cell cycle phases might influence our view of nuclear architecture.
- MeSH
- buněčné jadérko účinky léků genetika ultrastruktura MeSH
- buněčné linie MeSH
- Cajalova tělíska účinky léků genetika ultrastruktura MeSH
- chromozomální proteiny, nehistonové genetika metabolismus MeSH
- daktinomycin farmakologie MeSH
- fluorescenční barviva MeSH
- fluorescenční mikroskopie MeSH
- fotochemické procesy MeSH
- heterochromatin účinky léků genetika ultrastruktura MeSH
- histony genetika metabolismus MeSH
- inhibitory histondeacetylas farmakologie MeSH
- inhibitory syntézy proteinů farmakologie MeSH
- interfáze účinky léků genetika MeSH
- kyseliny hydroxamové farmakologie MeSH
- lidé MeSH
- messenger RNA biosyntéza MeSH
- mitóza účinky léků genetika MeSH
- myši MeSH
- zvířata MeSH
- Check Tag
- lidé MeSH
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
