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Esa Tyystjärvi - One of the best experts on this subject based on the ideXlab platform.
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Mathematical modelling of the light response curve of Photoinhibition of photosystem II.
Photosynthesis research, 2020Co-Authors: Esa Tyystjärvi, Marja Hakala, Paivi SarvikasAbstract:The light response curves of the acceptor and donor side mechanisms of Photoinhibition of Photosystem II were calculated, using Arabidopsis as a model organism. Acceptor-side Photoinhibition was modelled as double reduction of QA, noting that non-photochemical quenching has the same effect on the quantum yield of QA double reduction in closed PSII centres as it has on the quantum yield of electron transport in open centres. The light response curve of acceptor-side Photoinhibition in Arabidopsis shows very low efficiency under low intensity light and a relatively constant quantum yield above light saturation of photosynthesis. To calculate the light response curve of donor-side Photoinhibition, we built a model describing the concentration of the oxidized primary donor P680 + during steady-state photosynthesis. The model is based on literature values of rate constants of electron transfer reactions of PSII, and it was fitted with fluorescence parameters measured in the steady state. The modelling analysis showed that the quantum yield of donor-side Photoinhibition peaks under moderate light. The deviation of the acceptor and donor side mechanisms from the direct proportionality between Photoinhibition and photon flux density suggests that these mechanisms cannot solely account for Photoinhibition in vivo, but contribution of a reaction whose quantum yield is independent of light intensity is needed. Furthermore, a simple kinetic calculation suggests that the acceptor-side mechanism may not explain singlet oxygen production by photoinhibited leaves. The theoretical framework described here can be used to estimate the yields of different Photoinhibition mechanisms under different wavelengths or light intensities.
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Action Spectrum of Photoinhibition in the Diatom Phaeodactylum tricornutum.
Plant and Cell Physiology, 2017Co-Authors: Vesa Havurinne, Esa TyystjärviAbstract:: Light-dependent electron transfer is necessary for photosynthesis, but light also damages PSII. Light-induced damage to PSII is called Photoinhibition, and the damaging reactions of Photoinhibition are still under debate. Diatoms possess an exotic combination of light-harvesting pigments, Chls a/c and fucoxanthin, making them an interesting platform for studying the photoreceptors of Photoinhibition. We first confirmed the direct proportionality of Photoinhibition to the photon flux density of incident light in the diatom Phaeodactylum tricornutum. Phaeodactylum is known for its efficient non-photochemical quenching, and the effect of this photoprotective mechanism on Photoinhibition was tested. Photoinhibition proceeded essentially at the same rate in blue-light-grown Phaeodactylum cells that are capable of non-photochemical quenching and in red-light-grown, non-photochemical quenching-deficient cells. To obtain more insight into how the pigment composition of diatoms affects Photoinhibition, we measured the action spectrum of Photoinhibition in Phaeodactylum. In visible light, the action spectrum resembled the absorption spectrum of Phaeodactylum, and UV radiation caused much more Photoinhibition than visible light. Comparison of the action spectrum of Photoinhibition with the absorption spectrum and the excitation spectrum of 77 K PSII fluorescence emission confirmed that photosynthetic pigments are involved in Photoinhibition, but the photoinhibitory efficiency of red light is weak, suggesting that the role of light-harvesting pigments as light receptors of Photoinhibition is secondary. Finally, we compared Photoinhibition in Phaeodactylum with that in other photosynthetic organisms, and our data indicate that the PSII reaction centers of Phaeodactylum are not particularly well protected against the primary damage of Photoinhibition.
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Photoinhibition in marine picocyanobacteria.
Physiologia Plantarum, 2017Co-Authors: Arto J Soitamo, Vesa Havurinne, Esa TyystjärviAbstract:Marine Synechococcus and Prochlorococcus cyanobacteria have different antenna compositions although they are genetically near to each other, and different strains thrive in very different illumination conditions. We measured growth and Photoinhibition of PSII in two low-light and one high-light Prochlorococcus strains and in one Synechococcus strain. All strains were found to be able to shortly utilize moderate or even high light, but the low-light strains bleached rapidly in moderate light. Measurements of Photoinhibition in the presence of the antibiotic lincomycin showed that a low-light Prochlorococcus strain was more sensitive than a high-light strain and both were more sensitive than the marine Synechococcus. The action spectrum of Photoinhibition showed an increase from blue to ultraviolet wavelengths in all strains, suggesting contribution of manganese absorption to Photoinhibition, but blue light caused less Photoinhibition in marine cyanobacteria than expected on the basis of earlier results from plants and cyanobacteria. The visible-light part of the action spectrum resembled the absorption spectrum of the organism, suggesting that photosynthetic antenna pigments, especially divinyl chlorophylls, have a more important role as photoreceptors of visible-light Photoinhibition in marine cyanobacteria than in other photoautotrophs.
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Contributions of Visible and Ultraviolet Parts of Sunlight to Photoinhibition
Plant and Cell Physiology, 2010Co-Authors: Marja Hakala-yatkin, Mika Mäntysaari, Heta Mattila, Esa TyystjärviAbstract:Photoinhibition is light-induced inactivation of PSII, and action spectrum measurements have shown that UV light causes Photoinhibition much more efficiently than visible light. In the present study, we quantified the contribution of the UV part of sunlight in Photoinhibition of PSII in leaves. Greenhouse-grown pumpkin leaves were pretreated with lincomycin to block the repair of photoinhibited PSII, and exposed to sunlight behind a UV-permeable or UV-blocking filter. Oxygen evolution and Chl fluorescence measurements showed that Photoinhibition proceeds 35% more slowly under the UV-blocking than under the UV-permeable filter. Experiments with a filter that blocks UV-B but transmits UV-A and visible light revealed that UV-A light is almost fully responsible for the UV effect. The difference between leaves illuminated through a UV-blocking and UV-transparent filter disappeared when leaves of field-grown pumpkin plants were used. Thylakoids isolated from field-grown and greenhouse-grown plants were equally sensitive to UV light, and measurements of UV-induced fluorescence from leaves indicated that the protection of the field-grown plants was caused by substances that block the passage of UV light to the chloroplasts. Thus, the UV part of sunlight, especially the UV-A part, is potentially highly important in Photoinhibition of PSII but the UV-screening compounds of plant leaves may offer almost complete protection against UV-induced Photoinhibition.
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action spectrum of Photoinhibition in leaves of wild type and npq1 2 and npq4 1 mutants of arabidopsis thaliana
Plant and Cell Physiology, 2006Co-Authors: Paivi Sarvikas, Marja Hakala, Eija Patsikka, Taina Tyystjarvi, Esa TyystjärviAbstract:;Photoinhibition is light-induced inactivation of PSII. Hypotheses about the photoreceptor(s) of Photoinhibition include the Chl antenna of PSII, manganese of the oxygenevolving complex (OEC), uncoupled Chl and iron–sulfur centres. We measured the action spectrum of Photoinhibition in vivo from wild-type Arabidopsis thaliana L. and from the npq1-2 and npq4-1 mutants defective in nonphotochemical quenching (NPQ) of excitations of the PSII antenna. The in vivo action spectrum was found to resemble closely the in vitro action spectra published for Photoinhibition. We compared the action spectrum with absorbance spectra of model compounds of the OEC complex and other potential photoreceptors of Photoinhibition. The comparison suggests that both manganese and Chl function as photoreceptors in Photoinhibition. In accordance with the function of two types of photoreceptors in Photoinhibition, NPQ was found to offer only partial protection against Photoinhibition at visible wavelengths. The low protective efficiency of NPQ supports the conclusion that the Chl antenna of PSII is not the only photoreceptor of Photoinhibition. Comparison of the action spectrum of Photoinhibition with the emission spectrum of sunlight shows that the UV part of sunlight is responsible for the major part of Photoinhibition under natural conditions.
Shibao Zhang - One of the best experts on this subject based on the ideXlab platform.
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moderate Photoinhibition of photosystem ii significantly affects linear electron flow in the shade demanding plant panax notoginseng
Frontiers in Plant Science, 2018Co-Authors: Wei Huang, Shibao ZhangAbstract:Although Photoinhibition of photosystem II (PSII) frequently occurs under natural growing conditions, knowledge about the effect of moderate Photoinhibition on linear electron flow (LEF) remains controversial. Furthermore, mechanisms underlying the decrease in LEF upon PSII Photoinhibition are not well clarified. We examined how selective PSII Photoinhibition influenced LEF in the attached leaves of shade-demanding plant Panax notoginseng. After leaves were exposed to a high level of light (2258 μmol photons m-2 s-1) for 30 and 60 min, the maximum quantum yield of PSII (Fv/Fm) decreased by 17% and 23%, respectively, whereas the maximum photo-oxidizable P700 (Pm) remained stable. Therefore, this species displayed selective PSII photodamage under strong illumination. After these treatments, LEF was significantly decreased under all light levels but acidification of the thylakoid lumen changed only slightly. Furthermore, the decrease in LEF under low light was positively correlated with the extent of PSII Photoinhibition. Thus, the decline in LEF was not caused by the enhancement of lumenal acidification, but was induced by a decrease in PSII activity. These results indicate that residual PSII activity is an important determinant of LEF in this shade-adapted species, and they provide new insight into how strong illumination affects the growth of shade-demanding plants.
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Photoinhibition of photosystem i in nephrolepis falciformis depends on reactive oxygen species generated in the chloroplast stroma
Photosynthesis Research, 2018Co-Authors: Wei Huang, Mikko Tikkanen, Shibao ZhangAbstract:We studied how high light causes Photoinhibition of photosystem I (PSI) in the shade-demanding fern Nephrolepis falciformis, in an attempt to understand the mechanism of PSI Photoinhibition under natural field conditions. Intact leaves were treated with constant high light and fluctuating light. Detached leaves were treated with constant high light in the presence and absence of methyl viologen (MV). Chlorophyll fluorescence and P700 signal were determined to estimate Photoinhibition. PSI was highly oxidized under high light before treatments. N. falciformis showed significantly stronger Photoinhibition of PSI and PSII under constant high light than fluctuating light. These results suggest that high levels of P700 oxidation ratio cannot prevent PSI Photoinhibition under high light in N. falciformis. Furthermore, Photoinhibition of PSI in N. falciformis was largely accelerated in the presence of MV that promotes the production of superoxide anion radicals in the chloroplast stroma by accepting electrons from PSI. From these results, we propose that Photoinhibition of PSI in N. falciformis is mainly caused by superoxide radicals generated in the chloroplast stroma, which is different from the mechanism of PSI Photoinhibition in Arabidopsis thaliana and spinach. Here, we provide some new insights into the PSI Photoinhibition under natural field conditions.
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superoxide generated in the chloroplast stroma causes Photoinhibition of photosystem i in the shade establishing tree species psychotria henryi
Photosynthesis Research, 2017Co-Authors: Wei Huang, Yingjie Yang, Jiaolin Zhang, Hong Hu, Shibao ZhangAbstract:Our previous studies indicated that high light induced significant Photoinhibition of photosystem I (PSI) in the shade-establishing tree species Psychotria henryi. However, the underlying mechanism has not been fully clarified. In the present study, in order to investigate the mechanism of PSI Photoinhibition in P. henryi, we treated detached leaves with constant high light in the presence of methyl viologen (MV) or a soluble α-tocopherol analog, 2,2,5,7,8-pentamethyl-6-chromanol (PMC). We found that MV significantly depressed photochemical quantum yields in PSI and PSII when compared to PMC. On condition that no PSI Photoinhibition happened, although cyclic electron flow (CEF) was abolished in the MV-treated samples, P700 oxidation ratio was maintain at higher levels than the PMC-treated samples. In the presence of PMC, PSI Photoinhibition little changed but PSII Photoinhibition was significantly alleviated. Importantly, PSI Photoinhibition was largely accelerated in the presence of MV, which stimulates the production of superoxide and subsequently other reactive oxygen species at the chloroplast stroma by accepting electrons from PSI. Furthermore, MV largely aggravated PSII Photoinhibition when compared to control. These results suggest that high P700 oxidation ratio cannot prevent PSI Photoinhibition in P. henryi. Furthermore, the superoxide produced in the chloroplast stroma is critical for PSI Photoinhibition in the higher plant P. henryi, which is opposite to the mechanism underlying PSI Photoinhibition in Arabidopsis thaliana and spinach. These findings highlight a new mechanism of PSI Photoinhibition in higher plants.
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psi Photoinhibition is more related to electron transfer from psii to psi rather than psi redox state in psychotria rubra
Photosynthesis Research, 2016Co-Authors: Wei Huang, Yingjie Yang, Jiaolin Zhang, Hong Hu, Shibao ZhangAbstract:Although it has been believed that wild-type plants are capable of protecting photosystem I (PSI) under high light, our previous study indicates that PSI is sensitive to high light in the shade-established tree species Psychotria rubra. However, the underlying physiological mechanisms are unclear. In this study, we examined the roles of electron transfer from PSII to PSI and PSI redox state in PSI Photoinhibition in P. rubra by treatments with lincomycin (Lin), diuron (DCMU), and methyl viologen (MV). After exposure to 2000 μmol photons m−2 s−1 for 2 h, PSI activity decreased by 35, 29, 3, and 49 % in samples treated with H2O, Lin, DCMU, and MV, respectively. Meanwhile, the MV-treated samples showed higher P700 oxidation ratio than the H2O-treated samples, suggesting the PSI Photoinhibition under high light was accompanied by high levels of P700 oxidation ratio. PSI Photoinhibition was alleviated in the DCMU-treated samples but was accelerated in the MV-treated samples, suggesting that PSI Photoinhibition in P. rubra was mainly controlled by electron transfer from PSII to PSI. Taking together, PSI Photoinhibition is more related to electron transfer from PSII to PSI rather than PSI redox state in P. rubra, which is different from the mechanisms of PSI Photoinhibition in Arabidopsis thaliana and cucumber.
Norio Murata - One of the best experts on this subject based on the ideXlab platform.
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the mechanism of Photoinhibition in vivo re evaluation of the roles of catalase α tocopherol non photochemical quenching and electron transport
Biochimica et Biophysica Acta, 2012Co-Authors: Norio Murata, Suleyman I Allakhverdiev, Yoshitaka NishiyamaAbstract:Abstract Photoinhibition of photosystem II (PSII) occurs when the rate of light-induced inactivation (photodamage) of PSII exceeds the rate of repair of the photodamaged PSII. For the quantitative analysis of the mechanism of Photoinhibition of PSII, it is essential to monitor the rate of photodamage and the rate of repair separately and, also, to examine the respective effects of various perturbations on the two processes. This strategy has allowed the re-evaluation of the results of previous studies of Photoinhibition and has provided insight into the roles of factors and mechanisms that protect PSII from Photoinhibition, such as catalases and peroxidases, which are efficient scavengers of H2O2; α-tocopherol, which is an efficient scavenger of singlet oxygen; non-photochemical quenching, which dissipates excess light energy that has been absorbed by PSII; and the cyclic and non-cyclic transport of electrons. Early studies of Photoinhibition suggested that all of these factors and mechanisms protect PSII against photodamage. However, re-evaluation by the strategy mentioned above has indicated that, rather than protecting PSII from photodamage, they stimulate protein synthesis, with resultant repair of PSII and mitigation of Photoinhibition. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.
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protein synthesis is the primary target of reactive oxygen species in the Photoinhibition of photosystem ii
Physiologia Plantarum, 2011Co-Authors: Yoshitaka Nishiyama, Suleyman I Allakhverdiev, Norio MurataAbstract:Photoinhibition of photosystem II (PSII) occurs when the rate of photodamage to PSII exceeds the rate of the repair of photodamaged PSII. Recent examination of Photoinhibition by separate determinations of photodamage and repair has revealed that the rate of photodamage to PSII is directly proportional to the intensity of incident light and that the repair of PSII is particularly sensitive to the inactivation by reactive oxygen species (ROS). The ROS-induced inactivation of repair is attributable to the suppression of the synthesis de novo of proteins, such as the D1 protein, that are required for the repair of PSII at the level of translational elongation. Furthermore, molecular analysis has revealed that the ROS-induced suppression of protein synthesis is associated with the specific inactivation of elongation factor G via the formation of an intramolecular disulfide bond. Impairment of various mechanisms that protect PSII against Photoinhibition, including photorespiration, thermal dissipation of excitation energy, and the cyclic transport of electrons, decreases the rate of repair of PSII via the suppression of protein synthesis. In this review, we present a newly established model of the mechanism and the physiological significance of repair in the regulation of the Photoinhibition of PSII.
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a bacterial transgene for catalase protects translation of d1 protein during exposure of salt stressed tobacco leaves to strong light
Plant Physiology, 2007Co-Authors: Khaled Altaweel, Norio Murata, Toshio Iwaki, Yukinori Yabuta, Shigeru Shigeoka, Akira WadanoAbstract:During Photoinhibition of photosystem II (PSII) in cyanobacteria, salt stress inhibits the repair of photodamaged PSII and, in particular, the synthesis of the D1 protein (D1). We investigated the effects of salt stress on the repair of PSII and the synthesis of D1 in wild-type tobacco ( Nicotiana tabacum ‘Xanthi’) and in transformed plants that harbored the katE gene for catalase from Escherichia coli . Salt stress due to NaCl enhanced the Photoinhibition of PSII in leaf discs from both wild-type and katE- transformed plants, but the effect of salt stress was less significant in the transformed plants than in wild-type plants. In the presence of lincomycin, which inhibits protein synthesis in chloroplasts, the activity of PSII decreased rapidly and at similar rates in both types of leaf disc during Photoinhibition, and the observation suggests that repair of PSII was protected by the transgene-coded enzyme. Incorporation of [ 35 S]methionine into D1 during Photoinhibition was inhibited by salt stress, and the transformation mitigated this inhibitory effect. Northern blotting revealed that the level of psbA transcripts was not significantly affected by salt stress or by the transformation. Our results suggest that salt stress enhanced Photoinhibition by inhibiting repair of PSII and that the katE transgene increased the resistance of the chloroplast9s translational machinery to salt stress by scavenging hydrogen peroxide.
Wei Huang - One of the best experts on this subject based on the ideXlab platform.
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moderate Photoinhibition of photosystem ii significantly affects linear electron flow in the shade demanding plant panax notoginseng
Frontiers in Plant Science, 2018Co-Authors: Wei Huang, Shibao ZhangAbstract:Although Photoinhibition of photosystem II (PSII) frequently occurs under natural growing conditions, knowledge about the effect of moderate Photoinhibition on linear electron flow (LEF) remains controversial. Furthermore, mechanisms underlying the decrease in LEF upon PSII Photoinhibition are not well clarified. We examined how selective PSII Photoinhibition influenced LEF in the attached leaves of shade-demanding plant Panax notoginseng. After leaves were exposed to a high level of light (2258 μmol photons m-2 s-1) for 30 and 60 min, the maximum quantum yield of PSII (Fv/Fm) decreased by 17% and 23%, respectively, whereas the maximum photo-oxidizable P700 (Pm) remained stable. Therefore, this species displayed selective PSII photodamage under strong illumination. After these treatments, LEF was significantly decreased under all light levels but acidification of the thylakoid lumen changed only slightly. Furthermore, the decrease in LEF under low light was positively correlated with the extent of PSII Photoinhibition. Thus, the decline in LEF was not caused by the enhancement of lumenal acidification, but was induced by a decrease in PSII activity. These results indicate that residual PSII activity is an important determinant of LEF in this shade-adapted species, and they provide new insight into how strong illumination affects the growth of shade-demanding plants.
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Photoinhibition of photosystem i in nephrolepis falciformis depends on reactive oxygen species generated in the chloroplast stroma
Photosynthesis Research, 2018Co-Authors: Wei Huang, Mikko Tikkanen, Shibao ZhangAbstract:We studied how high light causes Photoinhibition of photosystem I (PSI) in the shade-demanding fern Nephrolepis falciformis, in an attempt to understand the mechanism of PSI Photoinhibition under natural field conditions. Intact leaves were treated with constant high light and fluctuating light. Detached leaves were treated with constant high light in the presence and absence of methyl viologen (MV). Chlorophyll fluorescence and P700 signal were determined to estimate Photoinhibition. PSI was highly oxidized under high light before treatments. N. falciformis showed significantly stronger Photoinhibition of PSI and PSII under constant high light than fluctuating light. These results suggest that high levels of P700 oxidation ratio cannot prevent PSI Photoinhibition under high light in N. falciformis. Furthermore, Photoinhibition of PSI in N. falciformis was largely accelerated in the presence of MV that promotes the production of superoxide anion radicals in the chloroplast stroma by accepting electrons from PSI. From these results, we propose that Photoinhibition of PSI in N. falciformis is mainly caused by superoxide radicals generated in the chloroplast stroma, which is different from the mechanism of PSI Photoinhibition in Arabidopsis thaliana and spinach. Here, we provide some new insights into the PSI Photoinhibition under natural field conditions.
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superoxide generated in the chloroplast stroma causes Photoinhibition of photosystem i in the shade establishing tree species psychotria henryi
Photosynthesis Research, 2017Co-Authors: Wei Huang, Yingjie Yang, Jiaolin Zhang, Hong Hu, Shibao ZhangAbstract:Our previous studies indicated that high light induced significant Photoinhibition of photosystem I (PSI) in the shade-establishing tree species Psychotria henryi. However, the underlying mechanism has not been fully clarified. In the present study, in order to investigate the mechanism of PSI Photoinhibition in P. henryi, we treated detached leaves with constant high light in the presence of methyl viologen (MV) or a soluble α-tocopherol analog, 2,2,5,7,8-pentamethyl-6-chromanol (PMC). We found that MV significantly depressed photochemical quantum yields in PSI and PSII when compared to PMC. On condition that no PSI Photoinhibition happened, although cyclic electron flow (CEF) was abolished in the MV-treated samples, P700 oxidation ratio was maintain at higher levels than the PMC-treated samples. In the presence of PMC, PSI Photoinhibition little changed but PSII Photoinhibition was significantly alleviated. Importantly, PSI Photoinhibition was largely accelerated in the presence of MV, which stimulates the production of superoxide and subsequently other reactive oxygen species at the chloroplast stroma by accepting electrons from PSI. Furthermore, MV largely aggravated PSII Photoinhibition when compared to control. These results suggest that high P700 oxidation ratio cannot prevent PSI Photoinhibition in P. henryi. Furthermore, the superoxide produced in the chloroplast stroma is critical for PSI Photoinhibition in the higher plant P. henryi, which is opposite to the mechanism underlying PSI Photoinhibition in Arabidopsis thaliana and spinach. These findings highlight a new mechanism of PSI Photoinhibition in higher plants.
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psi Photoinhibition is more related to electron transfer from psii to psi rather than psi redox state in psychotria rubra
Photosynthesis Research, 2016Co-Authors: Wei Huang, Yingjie Yang, Jiaolin Zhang, Hong Hu, Shibao ZhangAbstract:Although it has been believed that wild-type plants are capable of protecting photosystem I (PSI) under high light, our previous study indicates that PSI is sensitive to high light in the shade-established tree species Psychotria rubra. However, the underlying physiological mechanisms are unclear. In this study, we examined the roles of electron transfer from PSII to PSI and PSI redox state in PSI Photoinhibition in P. rubra by treatments with lincomycin (Lin), diuron (DCMU), and methyl viologen (MV). After exposure to 2000 μmol photons m−2 s−1 for 2 h, PSI activity decreased by 35, 29, 3, and 49 % in samples treated with H2O, Lin, DCMU, and MV, respectively. Meanwhile, the MV-treated samples showed higher P700 oxidation ratio than the H2O-treated samples, suggesting the PSI Photoinhibition under high light was accompanied by high levels of P700 oxidation ratio. PSI Photoinhibition was alleviated in the DCMU-treated samples but was accelerated in the MV-treated samples, suggesting that PSI Photoinhibition in P. rubra was mainly controlled by electron transfer from PSII to PSI. Taking together, PSI Photoinhibition is more related to electron transfer from PSII to PSI rather than PSI redox state in P. rubra, which is different from the mechanisms of PSI Photoinhibition in Arabidopsis thaliana and cucumber.
Xiaobing Chen - One of the best experts on this subject based on the ideXlab platform.
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Salt pretreatment alleviated salt-induced Photoinhibition in sweet sorghum
Theoretical and Experimental Plant Physiology, 2015Co-Authors: Shijie Zhao, Xiaobing ChenAbstract:Sweet sorghum is an important energy crop. This study aimed to investigate the effects of salt pretreatment on the interaction between photosystem II (PSII) and photosystem I (PSI) upon salt stress. In this study, sweet sorghum was pretreated with 150 mM NaCl for 10 days, and subsequently, the pretreated plants were subjected to severe salt stress at 300 mM NaCl. PSII and PSI Photoinhibition occurred in non-pretreated plants after 4 days of salt stress, as the maximum quantum yield of PSII (Fv/Fm) and the maximal photochemical capacity of PSI (Delta MR/MR0) significantly decreased, and their normal coordination was destroyed. The significant positive correlation between Fv/Fm and Delta MR/MR0 under salt stress indicated that PSII Photoinhibition was in relation to PSI Photoinhibition, and PSI Photoinhibition might lead to PSII Photoinhibition through inhibiting electron transport at the acceptor side of PSII. Salt stress did not induce PSII Photoinhibition in salt-pretreated plants, and thus, salt pretreatment protected PSI against Photoinhibition not by aggravating PSII Photoinhibition. Salt pretreatment mitigated the decrease in CO2 assimilation, reduced the feedback inhibition on photosynthetic electron transport and then contributed to suppressing PSI and PSII Photoinhibition in sweet sorghum under salt stress. Therefore, the normal coordination between PSII and PSI was maintained in salt-pretreated plants. In conclusion, salt pretreatment ensured normal PSII and PSI coordination by preventing Photoinhibition in sweet sorghum under salt stress.
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contrasting photosynthesis and Photoinhibition in tetraploid and its autodiploid honeysuckle lonicera japonica thunb under salt stress
Frontiers in Plant Science, 2015Co-Authors: Lihua Zhang, Congwen Wu, Xiaobing ChenAbstract:Honeysuckle (Lonicera japonica Thunb.) is a popular landscape plant. This study was to explore leaf photosynthetic characterization with emphasis on the coordination between photosystem II (PSII) and photosystem I (PSI) in tetraploid and its autodiploid honeysuckle (TH and DH) upon salt stress (300 mM NaCl). Leaf photosynthetic rate and carboxylation efficiency in DH and TH were significantly decreased under salt stress, and the decrease was greater in DH. PSII Photoinhibition was induced in DH under salt stress, as the maximum quantum yield of PSII (Fv/Fm) was significantly decreased. PSII Photoinhibition declined electron flow to PSI, but did not prevent PSI Photoinhibition, as the maximal photochemical capacity of PSI (Delta MR/MR0) was significantly decreased by salt stress. According to the significant decrease in PSI oxidation amplitude in the first 1 s red illumination, PSI Photoinhibition was more severe than PSII Photoinhibition. As a result, PSII and PSI coordination was destroyed. Comparatively, salt-induced Photoinhibition did not occur in TH, as no significant change was observed in Fv/Fm and Delta MR/MR0. Consequently, PSII and PSI coordination was not significantly affected by salt stress. In conclusion, TH maintained normal coordination between PSII and PSI by preventing Photoinhibition and exhibited higher leaf photosynthetic activity than DH under salt stress. Compared with DH, lower leaf ionic toxicity due to greater root Na+ extrusion and restriction of Na+ transport to leaf might be responsible for maintaining higher leaf photosynthetic capacity in TH under salt stress.
