When light absorbed by plants exceeds the capacity of photosynthesis, the xanthophyll violaxanthin is reversibly de-epoxidized to zeaxanthin in the so-called xanthophyll cycle. Zeaxanthin plays a key role in the prote...When light absorbed by plants exceeds the capacity of photosynthesis, the xanthophyll violaxanthin is reversibly de-epoxidized to zeaxanthin in the so-called xanthophyll cycle. Zeaxanthin plays a key role in the protection of photosynthetic organisms against excess light, by promoting rapidly reversible （qE） and long-term （ql） quenching of excited chlorophylls, and preventing lipid oxidation. The photoprotective role of zeaxanthin, either free or bound to light-harvesting complexes （Lhcs）, has been investigated by using mutants lacking Chl b （chl） and/or specific xanthophyll species （npq, lut2）. The chl mutation causes （1） the absence of Lhcb proteins; （2） strong reduction of the feedback deexcitation （qE）; and （3） accumulation of xanthophylls as free pigments into thylakoids. Chl mutants showed extreme sensitivity to photo-oxidative stress in high light, due to higher singlet oxygen （102） release. The double mutant chlnpql was more sensitive to photo-oxidation than chl, showing that zeaxanthin does protect lipids even when free in the membrane. Nevertheless, lack of zeaxanthin had a much stronger impact on the level of lipid peroxidation in Lhcs-containing plants （WTvs npql） with respect to Lhc-less plants （chl vs chlnpql）, implying that its protective effect is enhanced by interaction with antenna proteins. It is proposed that the antioxidant capacity of zeaxanthin is empowered in the presence of PSII- LHCs-Zea complexes, while its effect on enhancement of qE only provides a minor contribution. Comparison of the sensitivity of WT vs npql plants to exogenous 102 suggests that besides the scavenging of 102, at least one additional mechanism is involved in chloroplast photoprotection.展开更多
Energy transfer processes between two aggregates in a coupled chromophoric-pigment （protein） system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level...Energy transfer processes between two aggregates in a coupled chromophoric-pigment （protein） system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level system. The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate. The model can be used to theoretically simulate many aspects of light-harvesting complexes （LHCs）. By applying the real bio-parameters of photosynthesis, we numerically investigate the efficiency of energy transfer （EET） between the two aggregates in terms of some factors, e.g., the initial coherence of the donor aggregate, the coupling strengthes between the two aggregates and between different pigments, and the effects of noise from the environment. Our results provide evidence for that the actual numbers of pigments in the chromophoric tings of LHCs should be the optimum parameters for a high EET. We also give a detailed analysis of the effects of noise on the EET.展开更多
Plants as sessile organisms are continuously exposed to abiotic stress conditions that impose numerous detrimental effects and cause tremendous loss of yield. Abiotic stresses, including high sunlight, confer serious ...Plants as sessile organisms are continuously exposed to abiotic stress conditions that impose numerous detrimental effects and cause tremendous loss of yield. Abiotic stresses, including high sunlight, confer serious damage on the photosynthetic machinery of plants. Photosystem II （PSII） is one of the most susceptible components of the photosynthetic machinery that bears the brunt of abiotic stress. In addition to the generation of reactive oxygen species （ROS） by abiotic stress, ROS can also result from the absorption of excessive sunlight by the light-harvesting complex. ROS can damage the photosynthetic apparatus, particularly PSII, resulting in photoinhibition due to an imbalance in the photosynthetic redox signaling pathways and the inhibition of PSII repair. Designing plants with improved abiotic stress tolerance will require a comprehensive understanding of ROS signaling and the regulatory functions of various components, including protein kinases, transcription factors, and phytohormones, in the responses of photosynthetic machinery to abiotic stress. Bioenergetics approaches, such as chlorophyll a transient kinetics analysis, have facilitated our understanding of plant vitality and the assessment of PSII efficiency under adverse environmental conditions. This review discusses the current understanding and indicates potential areas of further studies on the regulation of the photosynthetic machinery under abiotic stress.展开更多
A green mutant was obtained among the chemically induced mutants of Rhodobacter sphaeroides 601 (RS601) and named GM309. A blue shift of 20 nm of the carotenoid absorption spectrum was found in the light-harvesting co...A green mutant was obtained among the chemically induced mutants of Rhodobacter sphaeroides 601 (RS601) and named GM309. A blue shift of 20 nm of the carotenoid absorption spectrum was found in the light-harvesting complex II (LH2) of GM309. Different from LH2 of RS601, it was found that the carotenoids in GM309-LH2 changed to be neurosporene by mutation. Neurosporene lacks a conjugate double bond, compared with the spheroidene in RS601-LH2 which has ten conjugate double bonds. As shown by absorption and circular dichroism spectroscopy, the overall structure of GM309-LH2 is little affected by this change. From fluorescence emission spectra, it is found that GM309-LH2 can transfer energy from carotenoids to Bchl-B850 without any change in efficiency. But the efficiency of energy transfer from B800 to B850 in GM309-LH2 is decreased to be 42% of that of the native. This work would provide a novel method to investigate the mechanism of excitation energy transfer in LH2.展开更多
The energy relaxation and kinetic evolution of transient spectra of bacteriochloro- phylls (BChls) in light-harvesting complex LH2 from Rb. sphaeroides 601 were investigated using femtosecond pump-probe technique. Upo...The energy relaxation and kinetic evolution of transient spectra of bacteriochloro- phylls (BChls) in light-harvesting complex LH2 from Rb. sphaeroides 601 were investigated using femtosecond pump-probe technique. Upon 783 nm excitation, the energy at B800 BChls ex-periences an intramolecular redistribution with 0.35 ps time constant before transferring to B850 BChls. With tuning the excitation wavelength, the dynamical evolution of excited BChls was clearly observed, which indicates an obvious competition between the ground state bleaching and excited state absorption (ESA) of BChls involved and an isosbestic point near 818 nm, and also demonstrates that from the lower electronic excited state of B800 BChls to the higher exci-tonic state of B850 BChls is an efficient routine for energy transfer. The excitation energy in higher excitonic states of B850 BChls relaxes rapidly to the next lowest excitonic state by inter-conversion, delocalization to adjacent molecular, populating the lowest excitonic state and the change of molecular conformation.展开更多
After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ （PSII） （FJF,, the ratio of variable to maximal fluorescence） decreased markedly and recovered basically to the l...After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ （PSII） （FJF,, the ratio of variable to maximal fluorescence） decreased markedly and recovered basically to the level before saturating light illumination after dark recovery for 3 h in both soybean and wheat leaves, indicating that the decline in FJ/Fm is a reversible down-regulation. Also, the saturating light illumination led to significant decreases in the low temperature （77 K） chlorophyll fluorescence parameters F685 （chlorophyll a fluorescence peaked at 685 nm） and F685/F735 （F735, chlorophyll a fluorescence peaked at 735 nm） in soybean leaves but not in wheat leaves. Moreover, trypsin （a protease） treatment resulted in a remarkable decrease in the amounts of PsbS protein （a nuclear gene psbS-encoded 22 kDa protein） in the thylakoids from saturating light-illuminated （SI）, but not in those from darkadapted （DT） and dark-recovered （DRT） soybean leaves. However, the treatment did not cause such a decrease in amounts of the PsbS protein in the thylakoids from saturating light-illuminated wheat leaves. These results support the conclusion that saturating light illumination induces a reversible dissociation of some light-harvesting complex Ⅱ （LHClI） from PSII reaction center complex in soybean leaf but not in wheat leaf.展开更多
文摘When light absorbed by plants exceeds the capacity of photosynthesis, the xanthophyll violaxanthin is reversibly de-epoxidized to zeaxanthin in the so-called xanthophyll cycle. Zeaxanthin plays a key role in the protection of photosynthetic organisms against excess light, by promoting rapidly reversible （qE） and long-term （ql） quenching of excited chlorophylls, and preventing lipid oxidation. The photoprotective role of zeaxanthin, either free or bound to light-harvesting complexes （Lhcs）, has been investigated by using mutants lacking Chl b （chl） and/or specific xanthophyll species （npq, lut2）. The chl mutation causes （1） the absence of Lhcb proteins; （2） strong reduction of the feedback deexcitation （qE）; and （3） accumulation of xanthophylls as free pigments into thylakoids. Chl mutants showed extreme sensitivity to photo-oxidative stress in high light, due to higher singlet oxygen （102） release. The double mutant chlnpql was more sensitive to photo-oxidation than chl, showing that zeaxanthin does protect lipids even when free in the membrane. Nevertheless, lack of zeaxanthin had a much stronger impact on the level of lipid peroxidation in Lhcs-containing plants （WTvs npql） with respect to Lhc-less plants （chl vs chlnpql）, implying that its protective effect is enhanced by interaction with antenna proteins. It is proposed that the antioxidant capacity of zeaxanthin is empowered in the presence of PSII- LHCs-Zea complexes, while its effect on enhancement of qE only provides a minor contribution. Comparison of the sensitivity of WT vs npql plants to exogenous 102 suggests that besides the scavenging of 102, at least one additional mechanism is involved in chloroplast photoprotection.
基金Project supported by the National Natural Science Foundation of China(Grant No.11174233)the National Basic Research Program of China(Grant No.2011CB311807)
文摘Energy transfer processes between two aggregates in a coupled chromophoric-pigment （protein） system are studied via the standard master equation approach. Each pigment of the two aggregates is modeled as a two-level system. The excitation energy is assumed to be transferred from the donor aggregate to the acceptor aggregate. The model can be used to theoretically simulate many aspects of light-harvesting complexes （LHCs）. By applying the real bio-parameters of photosynthesis, we numerically investigate the efficiency of energy transfer （EET） between the two aggregates in terms of some factors, e.g., the initial coherence of the donor aggregate, the coupling strengthes between the two aggregates and between different pigments, and the effects of noise from the environment. Our results provide evidence for that the actual numbers of pigments in the chromophoric tings of LHCs should be the optimum parameters for a high EET. We also give a detailed analysis of the effects of noise on the EET.
文摘Plants as sessile organisms are continuously exposed to abiotic stress conditions that impose numerous detrimental effects and cause tremendous loss of yield. Abiotic stresses, including high sunlight, confer serious damage on the photosynthetic machinery of plants. Photosystem II （PSII） is one of the most susceptible components of the photosynthetic machinery that bears the brunt of abiotic stress. In addition to the generation of reactive oxygen species （ROS） by abiotic stress, ROS can also result from the absorption of excessive sunlight by the light-harvesting complex. ROS can damage the photosynthetic apparatus, particularly PSII, resulting in photoinhibition due to an imbalance in the photosynthetic redox signaling pathways and the inhibition of PSII repair. Designing plants with improved abiotic stress tolerance will require a comprehensive understanding of ROS signaling and the regulatory functions of various components, including protein kinases, transcription factors, and phytohormones, in the responses of photosynthetic machinery to abiotic stress. Bioenergetics approaches, such as chlorophyll a transient kinetics analysis, have facilitated our understanding of plant vitality and the assessment of PSII efficiency under adverse environmental conditions. This review discusses the current understanding and indicates potential areas of further studies on the regulation of the photosynthetic machinery under abiotic stress.
文摘A green mutant was obtained among the chemically induced mutants of Rhodobacter sphaeroides 601 (RS601) and named GM309. A blue shift of 20 nm of the carotenoid absorption spectrum was found in the light-harvesting complex II (LH2) of GM309. Different from LH2 of RS601, it was found that the carotenoids in GM309-LH2 changed to be neurosporene by mutation. Neurosporene lacks a conjugate double bond, compared with the spheroidene in RS601-LH2 which has ten conjugate double bonds. As shown by absorption and circular dichroism spectroscopy, the overall structure of GM309-LH2 is little affected by this change. From fluorescence emission spectra, it is found that GM309-LH2 can transfer energy from carotenoids to Bchl-B850 without any change in efficiency. But the efficiency of energy transfer from B800 to B850 in GM309-LH2 is decreased to be 42% of that of the native. This work would provide a novel method to investigate the mechanism of excitation energy transfer in LH2.
基金the National Natural Science Foundation of China(Grant No.10274013)State Key Basic Research and Development Plan(Grant No.G1998010100)+1 种基金Natural Science Foundation of Henan Educational Committee(Grant No.20011400003)the Key Natural Science Foundation of Henan University.
文摘The energy relaxation and kinetic evolution of transient spectra of bacteriochloro- phylls (BChls) in light-harvesting complex LH2 from Rb. sphaeroides 601 were investigated using femtosecond pump-probe technique. Upon 783 nm excitation, the energy at B800 BChls ex-periences an intramolecular redistribution with 0.35 ps time constant before transferring to B850 BChls. With tuning the excitation wavelength, the dynamical evolution of excited BChls was clearly observed, which indicates an obvious competition between the ground state bleaching and excited state absorption (ESA) of BChls involved and an isosbestic point near 818 nm, and also demonstrates that from the lower electronic excited state of B800 BChls to the higher exci-tonic state of B850 BChls is an efficient routine for energy transfer. The excitation energy in higher excitonic states of B850 BChls relaxes rapidly to the next lowest excitonic state by inter-conversion, delocalization to adjacent molecular, populating the lowest excitonic state and the change of molecular conformation.
文摘After saturating light illumination for 3 h the potential photochemical efficiency of photosystem Ⅱ （PSII） （FJF,, the ratio of variable to maximal fluorescence） decreased markedly and recovered basically to the level before saturating light illumination after dark recovery for 3 h in both soybean and wheat leaves, indicating that the decline in FJ/Fm is a reversible down-regulation. Also, the saturating light illumination led to significant decreases in the low temperature （77 K） chlorophyll fluorescence parameters F685 （chlorophyll a fluorescence peaked at 685 nm） and F685/F735 （F735, chlorophyll a fluorescence peaked at 735 nm） in soybean leaves but not in wheat leaves. Moreover, trypsin （a protease） treatment resulted in a remarkable decrease in the amounts of PsbS protein （a nuclear gene psbS-encoded 22 kDa protein） in the thylakoids from saturating light-illuminated （SI）, but not in those from darkadapted （DT） and dark-recovered （DRT） soybean leaves. However, the treatment did not cause such a decrease in amounts of the PsbS protein in the thylakoids from saturating light-illuminated wheat leaves. These results support the conclusion that saturating light illumination induces a reversible dissociation of some light-harvesting complex Ⅱ （LHClI） from PSII reaction center complex in soybean leaf but not in wheat leaf.
