Thylakoids from mesophyll cells of maize showed a high rateof the ferredoxin (Fd)-dependent and antimycin A (AntiA)-sensitivecyclic electron flow as determined by the quenching of 9-aminoacridinefluorescence which indicates the formation of 相似文献
Photosynthesis Research - While subject to illumination, photosystem I (PSI) has the potential to produce reactive oxygen species (ROS) that can cause photo-oxidative damage in oxygenic... 相似文献
Cyclic electron transport (CET) is an attractive hypothesis for regulating photosynthetic electron transport and producing the additional ATP in oxygenic phototrophs. The concept of CET has been established in the last decades, and it is proposed to function in the progenitor of oxygenic photosynthesis, cyanobacteria. The in vivo activity of CET is frequently evaluated either from the redox state of the reaction center chlorophyll in photosystem (PS) I, P700, in the absence of PSII activity or by comparing PSI and PSII activities through the P700 redox state and chlorophyll fluorescence, respectively. The evaluation of CET activity, however, is complicated especially in cyanobacteria, where CET shares the intersystem chain, including plastoquinone, cytochrome b6/f complex, plastocyanin, and cytochrome c6, with photosynthetic linear electron transport (LET) and respiratory electron transport (RET). Here we sought to distinguish the in vivo electron transport rates in RET and CET in the cyanobacterium Synechocystis sp. PCC 6803. The reduction rate of oxidized P700 (P700+) decreased to less than 10% when PSII was inhibited, indicating that PSII is the dominant electron source to PSI but P700+ is also reduced by electrons derived from other sources. The oxidative pentose phosphate (OPP) pathway functions as the dominant electron source for RET, which was found to be inhibited by glycolaldehyde (GA). In the condition where the OPP pathway and respiratory terminal oxidases were inhibited by GA and KCN, the P700+ reduction rate was less than 1% of that without any inhibitors. This study indicate that the electron transport to PSI when PSII is inhibited is dominantly derived from the OPP pathway in Synechocystis sp. PCC 6803.
Ascorbate (AsA) peroxidase was found in six species of cyanobacteriaamong ten species tested. Upon the addition of H218O2 to thecells of AsA peroxidase-containing cyanobacteria, 16O2 derivedfrom water and 18O2 derived from H2I8O2 were evolved in thelight. The evolution of 16O2 was inhibited by DCMU and did notoccur in the dark, but I8O2 was evolved even in the dark orin the presence of DCMU. Similar light-dependent evolution of16O2 was observed in the cells of AsA peroxidase-containingEuglena and Chlamydomonas. However, the cells of AsA perox-idase-lackingcyanobacteria evolved only 18O2 in either the light or dark.Furthermore, the quenching of chlorophyll fluorescence inducedby hydrogen peroxide was observed only in the cells of the AsAperoxidase-containing Synechocystis 6803, and not in the cellsof Anacystis nidulans which lacks AsA peroxidase. Thus, cyanobacteriacan be divided into two groups, those that has and those thatlacks AsA peroxidase. The first group scavenges hydrogen peroxidewith the peroxidase using a photoreductant as the electron donor,and the second group only scavenges hydrogen peroxide with catalase. (Received July 23, 1990; Accepted October 18, 1990) 相似文献
Summary Formaldehyde dismutase was greatly stabilized by immobilization in a urethane prepolymer (PU-6). The immobilized enzyme exhibited stochiometrical dismutation of formaldehyde to methanol and formate in several repeated reactions. Conversion of methanol to formate occurred in a reaction with an immobilized enzyme system consisting of alcohol oxidase, catalase and formaldehyde dismutase, and with an intact cell-mixture of Hansenula polymorpha and Pseudomonas putida. Furthermore, the stability of the cell-mixture during repeated reactions was greatly improved by the immobilization, the 600 mM methanol added periodically being converted to formate in a 75% yield in 12 h. The immobilized cellsystem was also effective for the conversion of several aliphatic alcohols, C1 to C4, to the corresponding acids. 相似文献
Using thylakoid membranes, we previously demonstrated that accumulated electrons in the photosynthetic electron transport system induces the electron flow from the acceptor side of PSII to its donor side only in the presence of a pH gradient ((Delta)pH) across the thylakoid membranes. This electron flow has been referred to as cyclic electron flow within PSII (CEF-PSII) [Miyake and Yokota (2001) Plant Cell Physiol. 42: 508]. In the present study, we examined whether CEF-PSII operates in isolated intact chloroplasts from spinach leaves, by correlating the quantum yield of PSII [Phi(PSII)] with the activity of the linear electron flow [V(O(2))]. The addition of the protonophore nigericin to the intact chloroplasts decreased Phi(PSII), but increased V(O(2)), and relative electron flux in PSII [Phi(PSII) x PFD] and V(O(2)) were proportional to one another. Phi(PSII) x PFD at a given V(O(2)) was much higher in the presence of (Delta)pH than that in its absence. These effects of nigericin on the relationship between Phi(PSII) x PFD and V(O(2)) are consistent with those previously observed in thylakoid membranes, indicating the occurrence of CEF-PSII also in intact chloroplasts. In the presence of (Delta)pH, CEF-PSII accounted for the excess electron flux in PSII that could not be attributed to photosynthetic linear electron flow. The activity of CEF-PSII increased with increased light intensity and almost corresponded to that of the water-water cycle (WWC), implying that CEF-PSII can dissipate excess photon energy in cooperation with WWC to protect PSII from photoinhibition under limited photosynthesis conditions. 相似文献
The chloroplastic isoform of monodehydroascorbate (MDA) radical reductase was purified from spinach chloroplasts and leaves. The cDNA of chloroplastic MDA reductase was cloned, and its deduced amino acid sequence, consisting of 497 residues, showed high homology with those of putative organellar MDA reductases deduced from cDNAs of several plants. The amino acid sequence of the amino terminal of the purified enzyme suggested that the chloroplastic enzyme has a transit peptide consisting of 53 residues. A southern blot analysis suggested the occurrence of a gene encoding another isoform homologous to the chloroplastic isoform in spinach. The recombinant enzyme was highly expressed in Eschericia coli using the cDNA, and purified to a homogeneous state with high specific activity. The enzyme properties of the chloroplastic isoform are presented in comparison with those of the cytosolic form. 相似文献
Journal of Plant Research - Leaf nitrogen (N) level affects not only photosynthetic CO2 assimilation, but also two photosystems of the photosynthetic electron transport. The quantum yield of... 相似文献
Cell isolation by eliminating undesirable cell aggregations or colonies with low activity is essential to improve cell culture efficiency. Moreover, when creating tissues from induced pluripotent stem cells, residual undifferentiated cells must be removed to prevent tumor formation in vivo. Here, we evaluated the use of ultrasonic irradiation, which can apply energy locally without contact, and proposed a method to eliminate cells in a small area of culture by ultrasonic irradiation from a Langevin transducer. We constructed a device that incorporated a bolt‐clamped 19.84 kHz Langevin transducer with an ultrasonic horn and determined the optimal conditions for stable elimination of cells in small areas of a 35‐mm culture dish. The optimal conditions were as follows: number of cycles = 400, clearance distance = 1 mm, volume of medium = 4 mL, and distance from the center of culture surface = 0 mm. The mean cell elimination area under these conditions was 0.097 mm2. We also evaluated the viability of neighboring cells after ultrasonic irradiation by fluorescent staining and found that most cells around the elimination area survived. These findings suggest that the proposed method has potential for localized elimination of cells without the need for contact with the cell surface. 相似文献