Fresh potato (Solanum tuberosum L.) tuber slices had no capacity of the alternative respiration pathway (ARP). But this capacity could be induced drastically by a 24 h aging process. Western blotting results with a mo...Fresh potato (Solanum tuberosum L.) tuber slices had no capacity of the alternative respiration pathway (ARP). But this capacity could be induced drastically by a 24 h aging process. Western blotting results with a monoclonal antibody against the alternative oxidase (AOX) showed no evidence of AOX in fresh slices. However, an AOX protein of 36 kD was clearly detected in slices aged for 12 or 24 h(Fig.1). Under treatments with ACC and with CoCl 2, the ARP capacity of aged potato slices was enhanced and reduced, respectively. Correspondingly, the extent of AOX protein’s expression was enhanced by ACC and reduced by CoCl 2. The above results give evidence that the regulatory effect of endogenous ethylene on the development of ARP capacity in aging potato tuber slices is exerted through the induction of the expression of AOX therein.展开更多
An increase in ultraviolet （UV） B radiation on the earth＇s surface is a feature of current global climate changes. It has been reported that alternative oxidase （AOX） may have a protective role against oxidative ...An increase in ultraviolet （UV） B radiation on the earth＇s surface is a feature of current global climate changes. It has been reported that alternative oxidase （AOX） may have a protective role against oxidative stress induced by environmental stresses, such as UV-B. To better understand the characteristic tolerance of plants to UV-B radiation, the effects of enhanced UV-B radiation on the activity and expression of AOX in red kidney bean （Phaseolus vulgaris） leaves were investigated in the present study. The results show that the total respiration rate and AOX activity in red kidney bean leaves increased significantly during treatment with enhanced UV-B. However, cytochrome oxidase （COX） activity did not change significantly. The H2O2 content was also markedly increased and reached a maximum of 4.45 mmol·L^-1·g^-1 DW （dry weight） at 24 h of UV-B treatment, before dropping rapidly. Both alternative pathway content and alternative pathway activity were increased in the presence of exogenous H2O2. Immunoblotting analysis with anti-AOX monoclonal antibody revealed that expression of the AOX protein increased in red kidney bean leaves under enhanced UV-B radiation, reaching a peak at 72 h. In addition, AOX expression in red kidney bean leaves was induced by exogenous H2O2. These data indicate that the increase in AOX activity in red kidney bean leaves under enhanced UV-B radiation was mainly due to H2O2-induced AOX expression.展开更多
The mechanism by which the mitochondrial alternative oxidase （AOX） pathway contributes to photosystem II （PSII） photoprotection is in dispute. It was generally thought that the AOX pathway protects photosystems by...The mechanism by which the mitochondrial alternative oxidase （AOX） pathway contributes to photosystem II （PSII） photoprotection is in dispute. It was generally thought that the AOX pathway protects photosystems by dissipating excess reducing equivalents exported from chloroplasts through the malate/oxaloacetate （Mal/OAA） shuttle and thus preventing the over-reduction of chloroplasts. In this study, using the aoxla Arabidopsis mutant and nine other C3 and C4 plant species, we revealed an additional action model of the AOX pathway in PSII photoprotection. Although the AOX pathway contributes to PSII photoprotection in C3 leaves treated with high light, this contribution was observed to disappear when photorespiration was suppressed. Disruption or inhibition of the AOX pathway significantly decreased the photorespiration in C3 leaves. Moreover, the AOX pathway did not respond to high light and contributed little to PSII photoprotection in C4 leaves possessing a highly active Mal/OAA shuttle but with little photorespiration. These results demonstrate that the AOX pathway contributes to PSII photoprotection in C3 plants by maintaining photo- respiration to detoxify glycolate and via the indirect export of excess reducing equivalents from chloro-plasts by the MaI/OAA shuttle. This new action model explains why the AOX pathway does not contribute to PSII photoprotection in C4 plants.展开更多
Although mitochondrial alternative oxidase(AOX)has been proposed to play essential roles in high light stress tolerance,the effects of AOX on chlorophyll synthesis are unclear.Previous studies indicated that during gr...Although mitochondrial alternative oxidase(AOX)has been proposed to play essential roles in high light stress tolerance,the effects of AOX on chlorophyll synthesis are unclear.Previous studies indicated that during greening,chlorophyll accumulation was largely delayed in plants whose mitochondrial cyanide-resistant respiration was inhibited by knocking out nuclear encoded AOX gene.Here we show that this delay of chlorophyll accumulation was more significant under high light condition.Inhibition of cyanide-resistant respiration was also accompanied by the increase of plastid NADPH/NADP^+ratio,especially under high light treatment which subsequently blocked the import of multiple plastidial proteins,such as some components of the photosynthetic electron transport chain,the Calvin-Benson cycle enzymes and malate/oxaloacetate shuttle components.Over expression of AOXla rescued the aoxla mutant phenotype,including the chlorophyll accumulation during greening and plastidial protein import.It thus suggests that light intensity affects chlorophyll synthesis during greening process by a metabolic signal,the AOX-derived plastidial NADPH/NADP^+ratio change.And our results thus revealed a molecular mechanism of chloroplast-mitochondria interactions.展开更多
Salinity-imposed limitations on plant growth are manifested through osmotic and ionic imbalances. However, because salinity-induced responses vary considerably among crop plants, monitoring of such responses at an ear...Salinity-imposed limitations on plant growth are manifested through osmotic and ionic imbalances. However, because salinity-induced responses vary considerably among crop plants, monitoring of such responses at an early stage has relevance. In this study,physiological(seed germination, seed vigor index, root length, shoot length, fresh weight,dry weight) and biochemical attributes(osmoprotectants, K^+/Na^+ ratio) were analyzed for a time-course assessment of salt responses in Indian mustard(Brassica juncea L.) with an emphasis on early monitoring. The results showed strong correlations for total soluble sugars at germination phase(24 h), proline content in the seedling establishment phase(48 h) and various physiological parameters including seed vigor index(R^2= 0.901), shoot length(R^2= 0.982), and fresh weight(R^2= 0.980) at 72 h(adaptation under stress). In addition, transcriptional changes were observed under NaCl treatment for key genes belonging to the family of selective ion transporters(NHX, HKT) and abscisic acid synthesis(AAO-3). The status of mitochondrial respiration was also examined as a probe for salinity tolerance at an early stage. The results suggested that although all the analyzed parameters showed correlations(negative or positive) with salt stress magnitude, their critical response times differed, with most of the studied biochemical, physiological, or molecular markers providing valuable information only after radicle emergence, whereas mitochondrial respiration via alternative oxidase was useful for the early detection of salt responses.展开更多
In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalan...In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalanine synthase CYS-C1, catalyzing the conversion of cysteine and cyanide to hydrogen sulfide and β-cyanoalanine. The hydrogen sulfide released also inhibits the cytochrome c oxidase and needs to be detoxified by the O-acetylserine（thiol）lyase mitochondrial isoform, OAS-C, which catalyzes the incorporation of sulfide to O-acetylserine to produce cysteine, thus generating a cyclic pathway in the mitochondria. The loss of functional OAS-C isoforms causes phenotypic characteristics very similar to the loss of the CYS-C1 enzyme, showing defects in root hair formation. Genetic complementation with the OAS-Cgene rescues the impairment of root hair elongation, restoring the wild-type phenotype. The mitochondria compromise their capacity to properly detoxify cyanide and the resulting sulfide because the latter cannot re-assimilate into cysteine in the oas-c null mutant. Consequently, we observe an accumulation of sulfide and cyanide and of the alternative oxidase, which is unable to prevent the production of reactive oxygen species probably due to the accumulation of both toxic molecules. Our results allow us to suggest that the significance of OAS-C is related to its role in the proper sulfide and cyanide detoxification in mitochondria.展开更多
Complex I （the NADH：ubiquinone oxidoreductase） of the mitochondrial respiratory chain is a complicated, multi-subunit, membrane- bound assembly and contains more than 40 different proteins in higher plants. In this...Complex I （the NADH：ubiquinone oxidoreductase） of the mitochondrial respiratory chain is a complicated, multi-subunit, membrane- bound assembly and contains more than 40 different proteins in higher plants. In this paper, we characterize the Arabidopsis homologue （designated as AtCIB22） of the B22 subunit of eukaryotic mitochondriai Complex I. AtCIB22 is a single-copy gene and is highly con- served throughout eukaryotes. AtCIB22 protein is located in mitochondria and the AtC1B22 gene is widely expressed in different tissues. Mutant Arabidopsis plants with a disrupted AtC1B22 gene display pleiotropic phenotypes including shorter roots, smaller plants and de- layed flowering. Stress analysis indicates that the AtC1B22 mutants＇ seed germination and early seedling growth are severely inhibited by sucrose deprivation stress but more tolerant to ethanol stress. Molecular analysis reveals that in moderate knockdown AtCIB22 mutants, genes including cell redox proteins and stress related proteins are significantly up-regulated, and that in severe knockdown AtCIB22 mu- tants, the alternative respiratory pathways including NDA1, NDB2, AOXla and AtPUMP1 are remarkably elevated. These data demon- strate that AtCIB22 is essential for plant development and mitochondrial electron transport chains in Arabidopsis. Our findings also en- hance our understanding about the physiological role of Complex I in plants.展开更多
Endogenous ethylene production and alternative oxidase (AOX) protein expression in 'Royal Gala' apple fruits were investigated after treatments with cold ( 0℃ for 1 week) and heat ( 38℃ for 1 h). A ...Endogenous ethylene production and alternative oxidase (AOX) protein expression in 'Royal Gala' apple fruits were investigated after treatments with cold ( 0℃ for 1 week) and heat ( 38℃ for 1 h). A monoclonal antibody to the terminal oxidase of the alternative pathway from Sauromatum guttatum was used to identify the AOX protein in apple fruits. The molecular mass of AOX in 'Royal Gala' apple fruits is approximately 38 kDa, similar to those reported in tobacco and tomato. The cold treatment depressed the release of endogenous ethylene production before the climacteric ethylene production and obviously induced the expression of AOX protein expression. The heat treatment had the opposite effects on the ethylene production and AOX protein expression. In addition, the climax of endogenous ethylene production preceded the maximum AOX expression after the cold temperature treatment. It is therefore proposed that in climacteric fruits the production of induced ethylene is not coordinated with the level of AOX protein.展开更多
文摘Fresh potato (Solanum tuberosum L.) tuber slices had no capacity of the alternative respiration pathway (ARP). But this capacity could be induced drastically by a 24 h aging process. Western blotting results with a monoclonal antibody against the alternative oxidase (AOX) showed no evidence of AOX in fresh slices. However, an AOX protein of 36 kD was clearly detected in slices aged for 12 or 24 h(Fig.1). Under treatments with ACC and with CoCl 2, the ARP capacity of aged potato slices was enhanced and reduced, respectively. Correspondingly, the extent of AOX protein’s expression was enhanced by ACC and reduced by CoCl 2. The above results give evidence that the regulatory effect of endogenous ethylene on the development of ARP capacity in aging potato tuber slices is exerted through the induction of the expression of AOX therein.
基金the Doctoral Program of Higher Education of China(20050730017)Foundation of Science and Technology of Gansu Provlnce(3ZS051-A25-018).
文摘An increase in ultraviolet （UV） B radiation on the earth＇s surface is a feature of current global climate changes. It has been reported that alternative oxidase （AOX） may have a protective role against oxidative stress induced by environmental stresses, such as UV-B. To better understand the characteristic tolerance of plants to UV-B radiation, the effects of enhanced UV-B radiation on the activity and expression of AOX in red kidney bean （Phaseolus vulgaris） leaves were investigated in the present study. The results show that the total respiration rate and AOX activity in red kidney bean leaves increased significantly during treatment with enhanced UV-B. However, cytochrome oxidase （COX） activity did not change significantly. The H2O2 content was also markedly increased and reached a maximum of 4.45 mmol·L^-1·g^-1 DW （dry weight） at 24 h of UV-B treatment, before dropping rapidly. Both alternative pathway content and alternative pathway activity were increased in the presence of exogenous H2O2. Immunoblotting analysis with anti-AOX monoclonal antibody revealed that expression of the AOX protein increased in red kidney bean leaves under enhanced UV-B radiation, reaching a peak at 72 h. In addition, AOX expression in red kidney bean leaves was induced by exogenous H2O2. These data indicate that the increase in AOX activity in red kidney bean leaves under enhanced UV-B radiation was mainly due to H2O2-induced AOX expression.
文摘The mechanism by which the mitochondrial alternative oxidase （AOX） pathway contributes to photosystem II （PSII） photoprotection is in dispute. It was generally thought that the AOX pathway protects photosystems by dissipating excess reducing equivalents exported from chloroplasts through the malate/oxaloacetate （Mal/OAA） shuttle and thus preventing the over-reduction of chloroplasts. In this study, using the aoxla Arabidopsis mutant and nine other C3 and C4 plant species, we revealed an additional action model of the AOX pathway in PSII photoprotection. Although the AOX pathway contributes to PSII photoprotection in C3 leaves treated with high light, this contribution was observed to disappear when photorespiration was suppressed. Disruption or inhibition of the AOX pathway significantly decreased the photorespiration in C3 leaves. Moreover, the AOX pathway did not respond to high light and contributed little to PSII photoprotection in C4 leaves possessing a highly active Mal/OAA shuttle but with little photorespiration. These results demonstrate that the AOX pathway contributes to PSII photoprotection in C3 plants by maintaining photo- respiration to detoxify glycolate and via the indirect export of excess reducing equivalents from chloro-plasts by the MaI/OAA shuttle. This new action model explains why the AOX pathway does not contribute to PSII photoprotection in C4 plants.
基金supported by the National Nature Science Foundation of China(31070210,91017004)the Doctoral Foundation of the Ministry of Education(20110181110059 and 20120181130008)Sichuan and Chengdu Nature Science Foundation(2010JQ0080,11DXYB097JH-027 and2012JY0078)
文摘Although mitochondrial alternative oxidase(AOX)has been proposed to play essential roles in high light stress tolerance,the effects of AOX on chlorophyll synthesis are unclear.Previous studies indicated that during greening,chlorophyll accumulation was largely delayed in plants whose mitochondrial cyanide-resistant respiration was inhibited by knocking out nuclear encoded AOX gene.Here we show that this delay of chlorophyll accumulation was more significant under high light condition.Inhibition of cyanide-resistant respiration was also accompanied by the increase of plastid NADPH/NADP^+ratio,especially under high light treatment which subsequently blocked the import of multiple plastidial proteins,such as some components of the photosynthetic electron transport chain,the Calvin-Benson cycle enzymes and malate/oxaloacetate shuttle components.Over expression of AOXla rescued the aoxla mutant phenotype,including the chlorophyll accumulation during greening and plastidial protein import.It thus suggests that light intensity affects chlorophyll synthesis during greening process by a metabolic signal,the AOX-derived plastidial NADPH/NADP^+ratio change.And our results thus revealed a molecular mechanism of chloroplast-mitochondria interactions.
基金supported by departmental grants under the Plan Project of Nuclear Agriculture and Biotechnology Division(NA&BTD),Mumbai
文摘Salinity-imposed limitations on plant growth are manifested through osmotic and ionic imbalances. However, because salinity-induced responses vary considerably among crop plants, monitoring of such responses at an early stage has relevance. In this study,physiological(seed germination, seed vigor index, root length, shoot length, fresh weight,dry weight) and biochemical attributes(osmoprotectants, K^+/Na^+ ratio) were analyzed for a time-course assessment of salt responses in Indian mustard(Brassica juncea L.) with an emphasis on early monitoring. The results showed strong correlations for total soluble sugars at germination phase(24 h), proline content in the seedling establishment phase(48 h) and various physiological parameters including seed vigor index(R^2= 0.901), shoot length(R^2= 0.982), and fresh weight(R^2= 0.980) at 72 h(adaptation under stress). In addition, transcriptional changes were observed under NaCl treatment for key genes belonging to the family of selective ion transporters(NHX, HKT) and abscisic acid synthesis(AAO-3). The status of mitochondrial respiration was also examined as a probe for salinity tolerance at an early stage. The results suggested that although all the analyzed parameters showed correlations(negative or positive) with salt stress magnitude, their critical response times differed, with most of the studied biochemical, physiological, or molecular markers providing valuable information only after radicle emergence, whereas mitochondrial respiration via alternative oxidase was useful for the early detection of salt responses.
文摘In non-cyanogenic species, the main source of cyanide derives from ethylene and camalexin biosyntheses. In mitochondria, cyanide is a potent inhibitor of the cytochrome c oxidase and is metabolized by the β-cyanoalanine synthase CYS-C1, catalyzing the conversion of cysteine and cyanide to hydrogen sulfide and β-cyanoalanine. The hydrogen sulfide released also inhibits the cytochrome c oxidase and needs to be detoxified by the O-acetylserine（thiol）lyase mitochondrial isoform, OAS-C, which catalyzes the incorporation of sulfide to O-acetylserine to produce cysteine, thus generating a cyclic pathway in the mitochondria. The loss of functional OAS-C isoforms causes phenotypic characteristics very similar to the loss of the CYS-C1 enzyme, showing defects in root hair formation. Genetic complementation with the OAS-Cgene rescues the impairment of root hair elongation, restoring the wild-type phenotype. The mitochondria compromise their capacity to properly detoxify cyanide and the resulting sulfide because the latter cannot re-assimilate into cysteine in the oas-c null mutant. Consequently, we observe an accumulation of sulfide and cyanide and of the alternative oxidase, which is unable to prevent the production of reactive oxygen species probably due to the accumulation of both toxic molecules. Our results allow us to suggest that the significance of OAS-C is related to its role in the proper sulfide and cyanide detoxification in mitochondria.
基金supported by the National Basic Research Program of China (No. 2009CB941503)
文摘Complex I （the NADH：ubiquinone oxidoreductase） of the mitochondrial respiratory chain is a complicated, multi-subunit, membrane- bound assembly and contains more than 40 different proteins in higher plants. In this paper, we characterize the Arabidopsis homologue （designated as AtCIB22） of the B22 subunit of eukaryotic mitochondriai Complex I. AtCIB22 is a single-copy gene and is highly con- served throughout eukaryotes. AtCIB22 protein is located in mitochondria and the AtC1B22 gene is widely expressed in different tissues. Mutant Arabidopsis plants with a disrupted AtC1B22 gene display pleiotropic phenotypes including shorter roots, smaller plants and de- layed flowering. Stress analysis indicates that the AtC1B22 mutants＇ seed germination and early seedling growth are severely inhibited by sucrose deprivation stress but more tolerant to ethanol stress. Molecular analysis reveals that in moderate knockdown AtCIB22 mutants, genes including cell redox proteins and stress related proteins are significantly up-regulated, and that in severe knockdown AtCIB22 mu- tants, the alternative respiratory pathways including NDA1, NDB2, AOXla and AtPUMP1 are remarkably elevated. These data demon- strate that AtCIB22 is essential for plant development and mitochondrial electron transport chains in Arabidopsis. Our findings also en- hance our understanding about the physiological role of Complex I in plants.
基金Supported by the National Natural Science Foundation of China(No.39970 0 72 )
文摘Endogenous ethylene production and alternative oxidase (AOX) protein expression in 'Royal Gala' apple fruits were investigated after treatments with cold ( 0℃ for 1 week) and heat ( 38℃ for 1 h). A monoclonal antibody to the terminal oxidase of the alternative pathway from Sauromatum guttatum was used to identify the AOX protein in apple fruits. The molecular mass of AOX in 'Royal Gala' apple fruits is approximately 38 kDa, similar to those reported in tobacco and tomato. The cold treatment depressed the release of endogenous ethylene production before the climacteric ethylene production and obviously induced the expression of AOX protein expression. The heat treatment had the opposite effects on the ethylene production and AOX protein expression. In addition, the climax of endogenous ethylene production preceded the maximum AOX expression after the cold temperature treatment. It is therefore proposed that in climacteric fruits the production of induced ethylene is not coordinated with the level of AOX protein.
