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
The proton motive force formed across the thylakoid membrane accompanying the photosynthetic electron transport can be used to synthesize ATP from ADP and inorganic phosphate for carbon assimilation. The mechanism of ...The proton motive force formed across the thylakoid membrane accompanying the photosynthetic electron transport can be used to synthesize ATP from ADP and inorganic phosphate for carbon assimilation. The mechanism of this important process has been intensively studied. However, there are still many aspects unsolved. For example: What is the ratio between the ATP and NADPH formed in noncyclic photophosphorylation and can it meet the requirement of carbon assimilation? Is there any localized proton within thylakoid membrane and is it related to the effi-展开更多
During photosynthesis, photosynthetic electron transport generates a proton motive force （pmf） across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is compos...During photosynthesis, photosynthetic electron transport generates a proton motive force （pmf） across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential （△φ） and an osmotic component （△pH）. Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein （AtBest）, which is critical for pmf partitioning. While the △pH component was slightly reduced in atbest, the △φ component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching （NPQ） upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride （Cl^-） channels. Thus, our findings reveal an important Cl^- channel required for ion transport and homeo- stasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.展开更多
Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission (ms-DLE) during the course of state transitions which were indicated by the chlorophyll fluores...Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission (ms-DLE) during the course of state transitions which were indicated by the chlorophyll fluores-cence at room temperature and 77 K. When dark-adapted leaves were induced to stateⅠ with far-red light, Fm/Fo, F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly. However, during the induction to stateⅡ with red light, both Fm/Fo and F685/F735 decreased immedi-ately and the former were quicker than the latter. In this interval, the intensity of fast phase of ms-DLE increased to a maximum and then decreased to a lower value during the transition to stateⅡ. Nigericin, an uncoupler which elimi-nates the proton gradient across thylakoid membrane, inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to stateⅡ. Another uncoupler, valino-mycin, which eliminates the membrane potential, did not affect the changes of the intensity of fast phase. These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to stateⅡ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.展开更多
呼吸链的氧化磷酸化.系统由五种蛋白质—脂类的酶复合体组成:复合体Ⅰ——NADH:泛醌氧化还原酶;复合体Ⅱ——琥珀酸:泛醌氧化还原酶;复合体Ⅲ——泛醌醇:高铁细胞色素 C 氧化还原酶;复合体Ⅳ——亚铁细胞色素 C 氧化还原酶;复合体Ⅴ——...呼吸链的氧化磷酸化.系统由五种蛋白质—脂类的酶复合体组成:复合体Ⅰ——NADH:泛醌氧化还原酶;复合体Ⅱ——琥珀酸:泛醌氧化还原酶;复合体Ⅲ——泛醌醇:高铁细胞色素 C 氧化还原酶;复合体Ⅳ——亚铁细胞色素 C 氧化还原酶;复合体Ⅴ——ATP 合成酶。本文介绍了上述五个复合体的结构和功能研究进展,并用形象的图来表达它们的概念,如图1所示,从功能上来看,线粒体的氧化—磷酸化系统的五种酶复合体是相互作用着的.呼吸链的电子载体都是醌式结构(FMN、FAD、COQ)和过渡金属的复合物(铁硫蛋白等)。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.
基金Project supported by the National Natural Scienoe Foundation of China
文摘The proton motive force formed across the thylakoid membrane accompanying the photosynthetic electron transport can be used to synthesize ATP from ADP and inorganic phosphate for carbon assimilation. The mechanism of this important process has been intensively studied. However, there are still many aspects unsolved. For example: What is the ratio between the ATP and NADPH formed in noncyclic photophosphorylation and can it meet the requirement of carbon assimilation? Is there any localized proton within thylakoid membrane and is it related to the effi-
基金supported by the National Natural Science Foundation of China (31322007 and 31570239)the Hundred Talents Program of the Chinese Academy of Sciences
文摘During photosynthesis, photosynthetic electron transport generates a proton motive force （pmf） across the thylakoid membrane, which is used for ATP biosynthesis via ATP synthase in the chloroplast. The pmf is composed of an electric potential （△φ） and an osmotic component （△pH）. Partitioning between these components in chloroplasts is strictly regulated in response to fluctuating environments. However, our knowledge of the molecular mechanisms that regulate pmf partitioning is limited. Here, we report a bestrophin-like protein （AtBest）, which is critical for pmf partitioning. While the △pH component was slightly reduced in atbest, the △φ component was much greater in this mutant than in the wild type, resulting in less efficient activation of nonphotochemical quenching （NPQ） upon both illumination and a shift from low light to high light. Although no visible phenotype was observed in the atbest mutant in the greenhouse, this mutant exhibited stronger photoinhibition than the wild type when grown in the field. AtBest belongs to the bestrophin family proteins, which are believed to function as chloride （Cl^-） channels. Thus, our findings reveal an important Cl^- channel required for ion transport and homeo- stasis across the thylakoid membrane in higher plants. These processes are essential for fine-tuning photosynthesis under fluctuating environmental conditions.
基金supported by the National Natural Science Foundation of China(Grant No.30070064)the State Key Basic Research Development Plan Program(Grant No.G1998010100)
文摘Change of proton gradient across thylakoid membrane in soybean leaves was studied with millisecond delayed light emission (ms-DLE) during the course of state transitions which were indicated by the chlorophyll fluores-cence at room temperature and 77 K. When dark-adapted leaves were induced to stateⅠ with far-red light, Fm/Fo, F685/F735 and the intensity of fast phase of ms-DLE were af-fected slightly. However, during the induction to stateⅡ with red light, both Fm/Fo and F685/F735 decreased immedi-ately and the former were quicker than the latter. In this interval, the intensity of fast phase of ms-DLE increased to a maximum and then decreased to a lower value during the transition to stateⅡ. Nigericin, an uncoupler which elimi-nates the proton gradient across thylakoid membrane, inhib-ited the increase in the intensity of fast phase of ms-DLE during the transition to stateⅡ. Another uncoupler, valino-mycin, which eliminates the membrane potential, did not affect the changes of the intensity of fast phase. These results suggest that the prompt increase in the intensity of fast phase of ms-DLE at the beginning of transitions to stateⅡ is cor-related mainly with the proton gradient released from water oxidation in photosystemⅡ.
文摘呼吸链的氧化磷酸化.系统由五种蛋白质—脂类的酶复合体组成:复合体Ⅰ——NADH:泛醌氧化还原酶;复合体Ⅱ——琥珀酸:泛醌氧化还原酶;复合体Ⅲ——泛醌醇:高铁细胞色素 C 氧化还原酶;复合体Ⅳ——亚铁细胞色素 C 氧化还原酶;复合体Ⅴ——ATP 合成酶。本文介绍了上述五个复合体的结构和功能研究进展,并用形象的图来表达它们的概念,如图1所示,从功能上来看,线粒体的氧化—磷酸化系统的五种酶复合体是相互作用着的.呼吸链的电子载体都是醌式结构(FMN、FAD、COQ)和过渡金属的复合物(铁硫蛋白等)。
