Photosynthetic electron transport is coupled to proton translocation across the thylakoid membrane, re- sulting in the formation of a trans-thylakoid proton gradient （△pH） and membrane potential （△ψ）. Ion trans...Photosynthetic electron transport is coupled to proton translocation across the thylakoid membrane, re- sulting in the formation of a trans-thylakoid proton gradient （△pH） and membrane potential （△ψ）. Ion trans-porters and channels localized to the thylakoid membrane regulate the contribution of each component to the proton motive force （pmf）. Although both △pH and △ψ contribute to ATP synthesis as pmf, only ~pH downregulates photosynthetic electron transport via the acidification of the thylakoid lumen by inducing thermal dissipation of excessive absorbed light energy from photosystem II antennae and slowing down of the electron transport through the cytochrome bsf complex. To optimize the tradeoff between efficient light energy utilization and protection of both photosystems against photodamage, plants have to regulate the pmf amplitude and its components, △pH and △ψ. Cyclic electron transport around photosystem I （PSI） is a major regulator of the pmf amplitude by generating pmf independently of the net production of NADPH by linear electron transport. Chloroplast ATP synthase relaxes pmf for ATP synthesis, and its activity should be finely tuned for maintaining the size of the pmf during steady-state photosynthesis. Pseudo-cyclic electron transport mediated by flavodiiron protein （FIv） forms a large electron sink, which is essential for PSI photoprotection in fluctuating light in cyanobacteria. FIv is conserved from cyanobacteria to gymno- sperms but not in angiosperms. The Arabidopsis proton gradient regulation 50（pgr5） mutant is defective in the main pathway of PSI cyclic electron transport. By introducing Physcomitrella patens genes encoding Flvs, the function of PSI cyclic electron transport was substituted by that of FIv-dependent pseudo-cyclic electron transport. In transgenic plants, the size of the pmf was complemented to the wild-type level but the contribution of △pH to the total pmf was lower than that in the wild type. In the pgr5 mutant, the size of the pmf was drastically lowered by the absence of PSI cyclic electron transport. In the mutant, △pH occupied the majority ofpmf, suggesting the presence of a mechanism for the homeostasis of luminal pH in the light. To avoid damage to photosynthetic electron transport by periods of excess solar energy, plants employ an intricate regulatory network involving alternative electron transport pathways, ion transporters/channels, and pH-dependent mechanisms for downregulating photosynthetic electron transport.展开更多
Plants need tight regulation of photosynthetic electron transport for survival and growth under environ- mental and metabolic conditions. For this purpose, the linear electron transport （LET） pathway is supple- ment...Plants need tight regulation of photosynthetic electron transport for survival and growth under environ- mental and metabolic conditions. For this purpose, the linear electron transport （LET） pathway is supple- mented by a number of alternative electron transfer pathways and valves. In Arabidopsis, cyclic electron transport （CET） around photosystem I （PSI）, which recycles electrons from ferrodoxin to plastoquinone, is the most investigated alternative route. However, the interdependence of LET and CET and the relative importance of CET remain unclear, largely due to the difficulties in precise assessment of the contribution of CET in the presence of LET, which dominates electron flow under physiological conditions. We there- fore generated Arabidopsis mutants with a minimal water-splitting activity, and thus a low rate of LET, by combining knockout mutations in Psb01, PsbP2, PsbQ1, PsbQ2, and PsbR loci. The resulting 45 mutant is viable, although mature leaves contain only ~20% of wild-type naturally less abundant Psb02 protein. 45 plants compensate for the reduction in LET by increasing the rate of CET, and inducing a strong non-photochemical quenching （NPQ） response during dark-to-light transitions. To identify the molecular origin of such a high-capacity CET, we constructed three sextuple mutants lacking the qE component of NPQ （45 npq4-1）, NDH-mediated CET （45 crr4-3）, or PGR5-PGRLl-mediated CET （45 pgrS）. Their analysis revealed that PGR5-PGRLl-mediated CET plays a major role in ~pH formation and induction of NPQ in C3 plants. Moreover, while pgr5 dies at the seedling stage under fluctuating light conditions, 45 pgr5 plants are able to survive, which underlines the importance of PGR5 in modulating the intersystem electron transfer.展开更多
Spraying 1-2 mmol/L solution of NaHSO 3 on rice ( Oryza sativa L.) leaves resulted in the enhancement of net photosynthetic rate for more than three days. It was also observed that NaHSO 3 application caused incr...Spraying 1-2 mmol/L solution of NaHSO 3 on rice ( Oryza sativa L.) leaves resulted in the enhancement of net photosynthetic rate for more than three days. It was also observed that NaHSO 3 application caused increases both in ATP content in leaves and the millisecond_delayed light emission of leaves. The increase in net photosynthetic rate caused by NaHSO 3 treatment was similar to that by PMS (phenazine methosulfate) treatment. The grain yield of treated rice was enhanced approximately by 10% after duplicated application of NaHSO 3 in milk_ripening stage. It is suggested that the enhancement of photosynthesis by NaHSO 3 treatment resulted from the effect of increasing ATP supplement. Concomitant with an increase in the photosynthetic rate and ATP content in leaves, the transient increase in chlorophyll fluorescence after the termination of actinic light, which could be used as an index of the cyclic electron flow, was also enhanced by low concentration of NaHSO 3 treatment. Basing on these results it is proposed that the increase in rice photosynthesis caused by low concentrations of NaHSO 3 could be due to the stimulation of the cyclic electron flow around PSⅠ which in turn the enhancement of the coupled photophosphorylation and photosynthesis.展开更多
Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO2 assimilation rate decreased to 16% of the control after 20 d hig...Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO2 assimilation rate decreased to 16% of the control after 20 d high-temperature stress, and thus the absorption of photon energy exceeded the energy required for CO2 assimilation. The efficiency of excitation energy capture by open photosystem Ⅱ（PSⅡ） reaction centres （Fv＇/Fm＇） at moderate irradiance, photochemical quenching （qp）, and the quantum yield of PSII electron transport （φPSⅡ） were significantly lower after high-temperature stress. Nevertheless, non-photochemical quenching （qNP） and energy-dependent quenching （qE） were significantly higher under such conditions. The post-irradiation transient of chlorophyll （Chl） fluorescence significantly increased after the turnoff of the actinic light （AL）, and this increase was considerably higher in the 39 ℃-grown seedlings than in the 30 ~C-grown ones. The increased post-irradiation fluorescence points to enhanced cyclic electron transport around PSI under high growth temperature conditions, thus helping to dissipate excess photon energy non-radiatively.展开更多
Bisulfite at low concentrations(L-NaHSO3) increases cyclic electron transport around photosystem I(PSI) and photosynthesis.However,little is known regarding the detailed contribution of cyclic electron transport to th...Bisulfite at low concentrations(L-NaHSO3) increases cyclic electron transport around photosystem I(PSI) and photosynthesis.However,little is known regarding the detailed contribution of cyclic electron transport to the promoted photosynthesis by L-NaHSO3.In the present work,we used tobacco mutant defective in ndhC-ndhK-ndhJ(ndhCKJ) to investigate the role of NAD(P)H dehydrogenase(NDH)-dependent cyclic electron transport around PSI in an increase in photosynthesis by L-NaHSO3.After the treatment of tobacco leaves with L-NaHSO3(10 μmol L-1),the NDH-dependent cyclic electron transport,monitored by a transient post-illumination increase in Chl fluorescence and the amount of NDH,was notably up-regulated in wild type(WT).The NDH-dependent cyclic electron transport was severely impaired in ndhCKJ and was not significantly affected by treatment with L-NaHSO3.Accordingly,the NDH-dependent transthylakoid membrane proton gradient(pH),as reflected by the slow phase of millisecond-delayed light emission(ms-DLE),was increased by L-NaHSO3 in WT,but not in ndhCKJ;the enhancement of cyclic photophosphorylation(PSP) activity by L-NaHSO3 was more obvious in WT than ndhCKJ.The accumulation of both superoxide and hydrogen peroxide was reduced in WT when subjected to L-NaHSO3 treatment,but not in ndhCKJ.Furthermore,the increase of photosynthetic O 2 evolution rate by L-NaHSO3 was more significant in WT than in ndhCKJ.We therefore conclude that L-NaHSO3 alleviates the photo-oxidative damage by the enhancement of NDH-dependent cyclic PSP,thereby improving photosynthesis.展开更多
Cyclic electron transport/flow(CET/CEF)in chloroplasts is a regulatory process essential for the optimization of plant photosynthetic efficiency.A crucial CEF pathway is catalyzed by a membrane-embedded NADH dehydroge...Cyclic electron transport/flow(CET/CEF)in chloroplasts is a regulatory process essential for the optimization of plant photosynthetic efficiency.A crucial CEF pathway is catalyzed by a membrane-embedded NADH dehydrogenase-like(NDH)complex that contains at least 29 protein subunits and associates with photosystem I(PSI)to form the NDH-PSI supercomplex.Here,we report the 3.9Åresolution structure of the Arabidopsis thaliana NDH-PSI(AtNDH-PSI)supercomplex.We constructed structural models for 26 AtNDH subunits,among which 11 are unique to chloroplasts and stabilize the core part of the NDH complex.In the supercomplex,one NDH can bind up to two PSI-light-harvesting complex I(PSI-LHCI)complexes at both sides of its membrane arm.Two minor LHCIs,Lhca5 and Lhca6,each present in one PSI-LHCI,interact with NDH and contribute to supercomplex formation and stabilization.Collectively,our study reveals the structural details of the AtNDH-PSI supercomplex assembly and provides a molecular basis for further investigation of the regulatory mechanism of CEF in plants.展开更多
Cyanobacteria possess multiple,functionally distinct NADPH dehydrogenase(NDH-1)complexes.In this mini-review,we describe the cyanobacterial NDH-1 complexes by focusing on their identification,regulatory properties,and...Cyanobacteria possess multiple,functionally distinct NADPH dehydrogenase(NDH-1)complexes.In this mini-review,we describe the cyanobacterial NDH-1 complexes by focusing on their identification,regulatory properties,and multiple functions.The multiple functions can be divided into basic and extending functions,and the basic functions are compared with those in chloroplasts.Many questions related to cyanobacterial NDH-1 complexes remain unanswered and are briefly summarized here.展开更多
After incubation at 42℃ for more than 48 h, brown damages occurred on the stems of tobacco (Nicotiana tabacum L.) ndhC-ndhK-ndhJ deletion mutant (?ndhCKJ), followed by wilt of the leaves, while less the phenotype was...After incubation at 42℃ for more than 48 h, brown damages occurred on the stems of tobacco (Nicotiana tabacum L.) ndhC-ndhK-ndhJ deletion mutant (?ndhCKJ), followed by wilt of the leaves, while less the phenotype was found in its wild type (WT). Analysis of the kinetics of post-illumination rise in chlorophyll fluorescence indicated that the PSI cyclic electron flow and the chlororespiration mediated by NAD(P)H dehydrogenase (NDH) was significantly enhanced in WT under the high temperature. After leaf disks were treated with methyl viologen (MV), photosynthetic apparatus of ?ndhCKJ exhibited more severe photo-oxidative damage, even bleaching of chlorophyll. Analysis of P700 oxidation and reduction showed that the NDH mediated cyclic electron flow probably functioned as an electron competitor with Mehler reaction, to reduce the accumulation of reactive oxygen species (ROS). When leaf disks were heat stressed at 42℃ for 6 h, the photochemical activity declined more markedly in ?ndhCKJ than in WT, accompanied with more evident decrease in the amount of soluble Rubisco activase. In addition, the slow phase of millisecond-delayed light emission (ms-DLE) of chlorophyll fluorescence indicated that NDH was involved in the building-up of transthy-lakoid proton gradient (?pH), while the consumption of ?pH was highly inhibited in ?ndhCKJ after heat stress. Based on the results, we supposed that the cyclic electron flow mediated by NDH could be stimulated under the heat stressed conditions, to divert excess electrons via chlororespiration pathway, and sustain CO2 assimilation by providing extra ?pH, thus reducing the photooxidative damage.展开更多
CYCLIC electron transport around photosystem I (PS I ) is considered physiologically important not only for its coupled formation of ATP, but also for its function on protection of the photosynthetic apparatus against...CYCLIC electron transport around photosystem I (PS I ) is considered physiologically important not only for its coupled formation of ATP, but also for its function on protection of the photosynthetic apparatus against photoinhibition. However, due to the difficulty of its measurement, we know little about its operation in vivo.展开更多
文摘Photosynthetic electron transport is coupled to proton translocation across the thylakoid membrane, re- sulting in the formation of a trans-thylakoid proton gradient （△pH） and membrane potential （△ψ）. Ion trans-porters and channels localized to the thylakoid membrane regulate the contribution of each component to the proton motive force （pmf）. Although both △pH and △ψ contribute to ATP synthesis as pmf, only ~pH downregulates photosynthetic electron transport via the acidification of the thylakoid lumen by inducing thermal dissipation of excessive absorbed light energy from photosystem II antennae and slowing down of the electron transport through the cytochrome bsf complex. To optimize the tradeoff between efficient light energy utilization and protection of both photosystems against photodamage, plants have to regulate the pmf amplitude and its components, △pH and △ψ. Cyclic electron transport around photosystem I （PSI） is a major regulator of the pmf amplitude by generating pmf independently of the net production of NADPH by linear electron transport. Chloroplast ATP synthase relaxes pmf for ATP synthesis, and its activity should be finely tuned for maintaining the size of the pmf during steady-state photosynthesis. Pseudo-cyclic electron transport mediated by flavodiiron protein （FIv） forms a large electron sink, which is essential for PSI photoprotection in fluctuating light in cyanobacteria. FIv is conserved from cyanobacteria to gymno- sperms but not in angiosperms. The Arabidopsis proton gradient regulation 50（pgr5） mutant is defective in the main pathway of PSI cyclic electron transport. By introducing Physcomitrella patens genes encoding Flvs, the function of PSI cyclic electron transport was substituted by that of FIv-dependent pseudo-cyclic electron transport. In transgenic plants, the size of the pmf was complemented to the wild-type level but the contribution of △pH to the total pmf was lower than that in the wild type. In the pgr5 mutant, the size of the pmf was drastically lowered by the absence of PSI cyclic electron transport. In the mutant, △pH occupied the majority ofpmf, suggesting the presence of a mechanism for the homeostasis of luminal pH in the light. To avoid damage to photosynthetic electron transport by periods of excess solar energy, plants employ an intricate regulatory network involving alternative electron transport pathways, ion transporters/channels, and pH-dependent mechanisms for downregulating photosynthetic electron transport.
文摘Plants need tight regulation of photosynthetic electron transport for survival and growth under environ- mental and metabolic conditions. For this purpose, the linear electron transport （LET） pathway is supple- mented by a number of alternative electron transfer pathways and valves. In Arabidopsis, cyclic electron transport （CET） around photosystem I （PSI）, which recycles electrons from ferrodoxin to plastoquinone, is the most investigated alternative route. However, the interdependence of LET and CET and the relative importance of CET remain unclear, largely due to the difficulties in precise assessment of the contribution of CET in the presence of LET, which dominates electron flow under physiological conditions. We there- fore generated Arabidopsis mutants with a minimal water-splitting activity, and thus a low rate of LET, by combining knockout mutations in Psb01, PsbP2, PsbQ1, PsbQ2, and PsbR loci. The resulting 45 mutant is viable, although mature leaves contain only ~20% of wild-type naturally less abundant Psb02 protein. 45 plants compensate for the reduction in LET by increasing the rate of CET, and inducing a strong non-photochemical quenching （NPQ） response during dark-to-light transitions. To identify the molecular origin of such a high-capacity CET, we constructed three sextuple mutants lacking the qE component of NPQ （45 npq4-1）, NDH-mediated CET （45 crr4-3）, or PGR5-PGRLl-mediated CET （45 pgrS）. Their analysis revealed that PGR5-PGRLl-mediated CET plays a major role in ~pH formation and induction of NPQ in C3 plants. Moreover, while pgr5 dies at the seedling stage under fluctuating light conditions, 45 pgr5 plants are able to survive, which underlines the importance of PGR5 in modulating the intersystem electron transfer.
文摘Spraying 1-2 mmol/L solution of NaHSO 3 on rice ( Oryza sativa L.) leaves resulted in the enhancement of net photosynthetic rate for more than three days. It was also observed that NaHSO 3 application caused increases both in ATP content in leaves and the millisecond_delayed light emission of leaves. The increase in net photosynthetic rate caused by NaHSO 3 treatment was similar to that by PMS (phenazine methosulfate) treatment. The grain yield of treated rice was enhanced approximately by 10% after duplicated application of NaHSO 3 in milk_ripening stage. It is suggested that the enhancement of photosynthesis by NaHSO 3 treatment resulted from the effect of increasing ATP supplement. Concomitant with an increase in the photosynthetic rate and ATP content in leaves, the transient increase in chlorophyll fluorescence after the termination of actinic light, which could be used as an index of the cyclic electron flow, was also enhanced by low concentration of NaHSO 3 treatment. Basing on these results it is proposed that the increase in rice photosynthesis caused by low concentrations of NaHSO 3 could be due to the stimulation of the cyclic electron flow around PSⅠ which in turn the enhancement of the coupled photophosphorylation and photosynthesis.
基金supported by the Natural Science Foundation of Zhejiang Province, China (No. Y3090276)the Major Program of Science and Technology Department of Zhejiang Province, China (No. 2007C12023)the Scientific Research Foundation for PhD of Zhejiang Forestry University, China (No. 2007FR047)
文摘Dissipation mechanisms of excess photon energy under high-temperature stress were studied in a subtropical forest tree seedling, Ficus concinna. Net CO2 assimilation rate decreased to 16% of the control after 20 d high-temperature stress, and thus the absorption of photon energy exceeded the energy required for CO2 assimilation. The efficiency of excitation energy capture by open photosystem Ⅱ（PSⅡ） reaction centres （Fv＇/Fm＇） at moderate irradiance, photochemical quenching （qp）, and the quantum yield of PSII electron transport （φPSⅡ） were significantly lower after high-temperature stress. Nevertheless, non-photochemical quenching （qNP） and energy-dependent quenching （qE） were significantly higher under such conditions. The post-irradiation transient of chlorophyll （Chl） fluorescence significantly increased after the turnoff of the actinic light （AL）, and this increase was considerably higher in the 39 ℃-grown seedlings than in the 30 ~C-grown ones. The increased post-irradiation fluorescence points to enhanced cyclic electron transport around PSI under high growth temperature conditions, thus helping to dissipate excess photon energy non-radiatively.
基金supported by the National Key Basic Research Program of China (2009CB118504)the National Natural Science Foundation of China (30870183,31070215)
文摘Bisulfite at low concentrations(L-NaHSO3) increases cyclic electron transport around photosystem I(PSI) and photosynthesis.However,little is known regarding the detailed contribution of cyclic electron transport to the promoted photosynthesis by L-NaHSO3.In the present work,we used tobacco mutant defective in ndhC-ndhK-ndhJ(ndhCKJ) to investigate the role of NAD(P)H dehydrogenase(NDH)-dependent cyclic electron transport around PSI in an increase in photosynthesis by L-NaHSO3.After the treatment of tobacco leaves with L-NaHSO3(10 μmol L-1),the NDH-dependent cyclic electron transport,monitored by a transient post-illumination increase in Chl fluorescence and the amount of NDH,was notably up-regulated in wild type(WT).The NDH-dependent cyclic electron transport was severely impaired in ndhCKJ and was not significantly affected by treatment with L-NaHSO3.Accordingly,the NDH-dependent transthylakoid membrane proton gradient(pH),as reflected by the slow phase of millisecond-delayed light emission(ms-DLE),was increased by L-NaHSO3 in WT,but not in ndhCKJ;the enhancement of cyclic photophosphorylation(PSP) activity by L-NaHSO3 was more obvious in WT than ndhCKJ.The accumulation of both superoxide and hydrogen peroxide was reduced in WT when subjected to L-NaHSO3 treatment,but not in ndhCKJ.Furthermore,the increase of photosynthetic O 2 evolution rate by L-NaHSO3 was more significant in WT than in ndhCKJ.We therefore conclude that L-NaHSO3 alleviates the photo-oxidative damage by the enhancement of NDH-dependent cyclic PSP,thereby improving photosynthesis.
基金The project was funded by the Strategic Priority Research Program of the CAS(XDB27020106)the National Natural Science Foundation of China(31930064,31970264,31770778)+3 种基金the CAS Project for Young Scientists in Basic Research(#YSBR-015)the National Key R&D Program of China(2017YFA0503702)R.B.and L.D.thank the University of Verona(grant RIBA 2017 to R.B.)MUR(grant PRIN 2018 to L.D.)for financial support.X.S.,D.C.and X.P.are sponsored by the Youth Innovation Promotion Association at the Chinese Academy of Sciences(2018123,2018124 and 2018128).
文摘Cyclic electron transport/flow(CET/CEF)in chloroplasts is a regulatory process essential for the optimization of plant photosynthetic efficiency.A crucial CEF pathway is catalyzed by a membrane-embedded NADH dehydrogenase-like(NDH)complex that contains at least 29 protein subunits and associates with photosystem I(PSI)to form the NDH-PSI supercomplex.Here,we report the 3.9Åresolution structure of the Arabidopsis thaliana NDH-PSI(AtNDH-PSI)supercomplex.We constructed structural models for 26 AtNDH subunits,among which 11 are unique to chloroplasts and stabilize the core part of the NDH complex.In the supercomplex,one NDH can bind up to two PSI-light-harvesting complex I(PSI-LHCI)complexes at both sides of its membrane arm.Two minor LHCIs,Lhca5 and Lhca6,each present in one PSI-LHCI,interact with NDH and contribute to supercomplex formation and stabilization.Collectively,our study reveals the structural details of the AtNDH-PSI supercomplex assembly and provides a molecular basis for further investigation of the regulatory mechanism of CEF in plants.
基金This work was partially supported by the National Natural Science Foundation of China(Grant No.30770175)the Shanghai Natural Science Foundation(No.07ZR14086)+2 种基金the Innovation Program of Shanghai Municipal Education Commission(No.08ZZ67)the Key Fundamental Project of Shanghai(No.06JC14091)the Leading Academic Discipline Project of Shanghai Municipal Education Commission(No.J50401).
文摘Cyanobacteria possess multiple,functionally distinct NADPH dehydrogenase(NDH-1)complexes.In this mini-review,we describe the cyanobacterial NDH-1 complexes by focusing on their identification,regulatory properties,and multiple functions.The multiple functions can be divided into basic and extending functions,and the basic functions are compared with those in chloroplasts.Many questions related to cyanobacterial NDH-1 complexes remain unanswered and are briefly summarized here.
基金supported in part by the National Natural Science Foundation of China(Grant Nos.30270123&90306013).
文摘After incubation at 42℃ for more than 48 h, brown damages occurred on the stems of tobacco (Nicotiana tabacum L.) ndhC-ndhK-ndhJ deletion mutant (?ndhCKJ), followed by wilt of the leaves, while less the phenotype was found in its wild type (WT). Analysis of the kinetics of post-illumination rise in chlorophyll fluorescence indicated that the PSI cyclic electron flow and the chlororespiration mediated by NAD(P)H dehydrogenase (NDH) was significantly enhanced in WT under the high temperature. After leaf disks were treated with methyl viologen (MV), photosynthetic apparatus of ?ndhCKJ exhibited more severe photo-oxidative damage, even bleaching of chlorophyll. Analysis of P700 oxidation and reduction showed that the NDH mediated cyclic electron flow probably functioned as an electron competitor with Mehler reaction, to reduce the accumulation of reactive oxygen species (ROS). When leaf disks were heat stressed at 42℃ for 6 h, the photochemical activity declined more markedly in ?ndhCKJ than in WT, accompanied with more evident decrease in the amount of soluble Rubisco activase. In addition, the slow phase of millisecond-delayed light emission (ms-DLE) of chlorophyll fluorescence indicated that NDH was involved in the building-up of transthy-lakoid proton gradient (?pH), while the consumption of ?pH was highly inhibited in ?ndhCKJ after heat stress. Based on the results, we supposed that the cyclic electron flow mediated by NDH could be stimulated under the heat stressed conditions, to divert excess electrons via chlororespiration pathway, and sustain CO2 assimilation by providing extra ?pH, thus reducing the photooxidative damage.
文摘CYCLIC electron transport around photosystem I (PS I ) is considered physiologically important not only for its coupled formation of ATP, but also for its function on protection of the photosynthetic apparatus against photoinhibition. However, due to the difficulty of its measurement, we know little about its operation in vivo.
