During the millions of years of evolution, photosynthetic organisms have adapted to almost all terrestrial and aquatic habitats, although some environments are obviously more suitable for photosynthesis than others. Photosynthetic organisms living in low-light conditions require on the one hand a large light-harvesting apparatus to absorb as many photons as possible. On the other hand, the excitation trapping time scales with the size of the light-harvesting system, and the longer the distance over which the formed excitations have to be transferred, the larger the probability to lose excitations. Therefore a compromise between photon capture efficiency and excitation trapping efficiency needs to be found. Here we report results on the whole cells of the green sulfur bacterium Chlorobaculum tepidum. Its efficiency of excitation energy transfer and charge separation enables the organism to live in environments with very low illumination. Using fluorescence measurements with picosecond resolution, we estimate that despite a rather large size and complex composition of its light-harvesting apparatus, the quantum efficiency of its photochemistry is around ~87% at 20 °C, ~83% at 45 °C, and about ~81% at 77 K when part of the excitation energy is trapped by low-energy bacteriochlorophyll a molecules. The data are evaluated using target analysis, which provides further insight into the functional organization of the low-light adapted photosynthetic apparatus.
- MeSH
- bakteriochlorofyl A fyziologie MeSH
- Chlorobi fyziologie MeSH
- fluorescence MeSH
- fluorometrie metody MeSH
- fotochemie * MeSH
- fotosyntéza * MeSH
- fyziologická adaptace MeSH
- přenos energie fyziologie MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Photosynthetic eukaryotes whose cells harbor plastids originating from secondary endosymbiosis of a red alga include species of major ecological and economic importance. Since utilization of solar energy relies on the efficient light-harvesting, one of the critical factors for the success of the red lineage in a range of environments is to be found in the adaptability of the light-harvesting machinery, formed by the proteins of the light-harvesting complex (LHC) family. A number of species are known to employ mainly a unique class of LHC containing red-shifted chlorophyll a (Chl a) forms absorbing above 690 nm. This appears to be an adaptation to shaded habitats. Here we present a detailed investigation of excitation energy flow in the red-shifted light-harvesting antenna of eustigmatophyte Trachydiscus minutus using time-resolved fluorescence and ultrafast transient absorption measurements. The main carotenoid in the complex is violaxanthin, hence this LHC is labeled the red-violaxanthin-Chl a protein, rVCP. Both the carotenoid-to-Chl a energy transfer and excitation dynamics within the Chl a manifold were studied and compared to the related antenna complex, VCP, that lacks the red-Chl a. Two spectrally defined carotenoid pools were identified in the red antenna, contributing to energy transfer to Chl a, mostly via S2 and hot S1 states. Also, Chl a triplet quenching by carotenoids is documented. Two separate pools of red-shifted Chl a were resolved, one is likely formed by excitonically coupled Chl a molecules. The structural implications of these observations are discussed.
- MeSH
- chlorofyl a * MeSH
- Chlorophyta fyziologie MeSH
- fluorescenční spektrometrie metody MeSH
- Heterokontophyta fyziologie MeSH
- plastidy MeSH
- přenos energie fyziologie MeSH
- Rhodophyta fyziologie MeSH
- světlosběrné proteinové komplexy chemie MeSH
- xanthofyly MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
In the present work, we report the first comparative spectroscopic investigation between Photosystem I (PSI) complexes isolated from two red clade algae. Excitation energy transfer was measured in PSI from Chromera velia, an alga possessing a split PsaA protein, and from the model diatom Phaeodactylum tricornutum. In both cases, the estimated effective photochemical trapping time was in the 15-25ps range, i.e. twice as fast as higher plants. In contrast to green phototrophs, the trapping time was rather constant across the whole emission spectrum. The weak wavelength dependence was attributed to the limited presence of long-wavelength emitting chlorophylls, as verified by low temperature spectroscopy. As the trapping kinetics of C. velia PSI were barely distinguishable from those of P. tricornutum PSI, it was concluded that the scission of PsaA protein had no significant impact on the overall PSI functionality. In conclusion, the two red clade algae analysed here, carried amongst the most efficient charge separation so far reported for isolated Photosystems.
- MeSH
- Alveolata metabolismus MeSH
- chlorofyl metabolismus MeSH
- fluorescenční spektrometrie MeSH
- fotosystém I (proteinový komplex) metabolismus MeSH
- kinetika MeSH
- přenos energie fyziologie MeSH
- Rhodophyta metabolismus MeSH
- rozsivky metabolismus MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Singlet oxygen (1O2) is formed by triplet-triplet energy transfer from triplet chlorophyll to O2 via Type II photosensitization reaction in photosystem II (PSII). Formation of triplet chlorophyll is associated with the change in spin state of the excited electron and recombination of triplet radical pair in the PSII antenna complex and reaction center, respectively. Here, we have provided evidence for the formation of 1O2 by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex. Protein hydroperoxide is formed by protein oxidation initiated by highly oxidizing chlorophyll cation radical and hydroxyl radical formed by Type I photosensitization reaction. Under highly oxidizing conditions, protein hydroperoxide is oxidized to protein peroxyl radical which either cyclizes to dioxetane or recombines with another protein peroxyl radical to tetroxide. These highly unstable intermediates decompose to triplet carbonyls which transfer energy to O2 forming 1O2. Data presented in this study show for the first time that 1O2 is formed by decomposition of protein hydroperoxide in PSII membranes deprived of Mn4O5Ca complex.
- MeSH
- chlorofyl metabolismus MeSH
- elektronová paramagnetická rezonance metody MeSH
- fotosystém II (proteinový komplex) metabolismus MeSH
- kyslík metabolismus MeSH
- oxidace-redukce MeSH
- peroxid vodíku metabolismus MeSH
- peroxidy metabolismus MeSH
- přenos energie fyziologie MeSH
- singletový kyslík metabolismus MeSH
- světlo MeSH
- světlosběrné proteinové komplexy metabolismus MeSH
- Publikační typ
- časopisecké články MeSH
- Klíčová slova
- Oberon-Titanium,
- MeSH
- biofyzikální jevy fyziologie MeSH
- lidé MeSH
- parapsychologie přístrojové vybavení MeSH
- přenos energie fyziologie MeSH
- psychofyzika přístrojové vybavení MeSH
- výzkum přístrojové vybavení MeSH
- Check Tag
- lidé MeSH
The aims of this study were to create a regression model of the relationship between load and muscle power output and to determine an optimal load for maximum power output during a countermovement squat and a bench press. 55 males and 48 females performed power testing at 0, 10, 30, 50, 70, 90, and 100% of their individual one-repetition maximum (1-RM) in the countermovement squat and bench press exercises. Values for the maximum dynamic strength and load for each lift were used to develop a regression model in which the ratio of power was predicted from the ratio of the load for each type of lift. By optimizing the regression model, we predicted the optimal load for maximum muscle power. For the bench press and the countermovement squat, the mean optimal loads for maximum muscle output ranged from 50 to 70% of maximum dynamic strength. Optimal load in the acceleration phase of the upward movement of the two exercises appeared to be more important than over the full range of the movement. This model allows for specific determination of the optimal load for a pre-determined power output.
- MeSH
- biologické modely MeSH
- dospělí MeSH
- fyzická vytrvalost fyziologie MeSH
- kosterní svaly fyziologie MeSH
- lidé MeSH
- počítačová simulace MeSH
- přenos energie fyziologie MeSH
- regresní analýza MeSH
- statistické modely MeSH
- svalová kontrakce fyziologie MeSH
- zatížení muskuloskeletálního systému fyziologie MeSH
- Check Tag
- dospělí MeSH
- lidé MeSH
- mužské pohlaví MeSH
- ženské pohlaví MeSH
- Publikační typ
- práce podpořená grantem MeSH
- MeSH
- bakteriální proteiny genetika imunologie metabolismus MeSH
- biochemické jevy fyziologie genetika imunologie MeSH
- biomedicínský výzkum * metody trendy MeSH
- fosfáty analýza metabolismus MeSH
- lidé MeSH
- makromolekulární látky * izolace a purifikace metabolismus MeSH
- modely genetické MeSH
- přenos energie fyziologie genetika imunologie MeSH
- proteosyntéza genetika imunologie MeSH
- replikace DNA fyziologie genetika imunologie MeSH
- statistika jako téma MeSH
- Check Tag
- lidé MeSH
- MeSH
- ATPázy spojené s různými buněčnými aktivitami fyziologie MeSH
- biologický transport fyziologie MeSH
- biologie buňky * dějiny trendy MeSH
- buněčná membrána * fyziologie klasifikace MeSH
- lidé MeSH
- molekulární biologie metody MeSH
- přenos energie fyziologie MeSH
- struktury buněčné membrány fyziologie MeSH
- vývojová biologie metody trendy MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- přehledy MeSH
