Research Interests:
The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and... more
The composition of antioxidant enzymes, especially superoxide dismutase (SOD), was studied in one nontransgenic and three transgenic lines of nodulated alfalfa plants. Transgenic lines overproduced MnSOD in the mitochondria of nodules and leaves (line 1–10), MnSOD in the chloroplasts (line 4–6), and FeSOD in the chloroplasts (line 10–7). In nodules of line 10–7, the absence of transgene-encoded FeSOD activity was due to a lack of mRNA, whereas in nodules of line 4-6 the absence of transgene-encoded MnSOD activity was due to enzyme inactivation or degradation. Transgenic alfalfa showed a novel compensatory effect in the activities of MnSOD (mitochondrial) and FeSOD (plastidic) in the leaves, which was not caused by changes in the mRNA levels. These findings imply that SOD activity in plant tissues and organelles is regulated, at least partially, at the posttranslational level. All four lines had low CuZnSOD activities and an abundant FeSOD isozyme, especially in nodules, indicating t...
Research Interests: Biochemistry, Genetics, Microbiology, Biology, Mitochondria, and 15 moreMedicine, Antioxidants, Catalase, Iron, Molecular Plant Microbe Interactions, Isoenzymes, Enzyme activity, Amino Acid Sequence, Base Sequence, Chloroplast, Isozyme, Chloroplasts, Mitochondrion, Molecular Sequence Data, and Medicago sativa
Research Interests: Genetics, Biology, Medicine, Biological Sciences, Saccharomyces cerevisiae, and 15 morePhylogeny, Plant Physiology, Lotus, Plant, Alternative splicing, Gene, Gene Duplication, Plant Roots, Cadmium, Intron, Alternative Splicing, Protein isoforms, Amino Acid Sequence, Molecular Sequence Data, and Lotus japonicus
Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon metabolism and oxidative stress in the decline of nitrogenase (N2ase) activity. Exposure of plants to a moderate drought (leaf water potential... more
Alfalfa (Medicago sativa) plants were exposed to drought to examine the involvement of carbon metabolism and oxidative stress in the decline of nitrogenase (N2ase) activity. Exposure of plants to a moderate drought (leaf water potential of −1.3 MPa) had no effect on sucrose (Suc) synthase (SS) activity, but caused inhibition of N2ase activity (−43%), accumulation of succinate (+36%) and Suc (+58%), and up-regulation of genes encoding cytosolic CuZn-superoxide dismutase (SOD), plastid FeSOD, cytosolic glutathione reductase, and bacterial MnSOD and catalases B and C. Intensification of stress (−2.1 MPa) decreased N2ase (−82%) and SS (−30%) activities and increased malate (+40%), succinate (+68%), and Suc (+435%). There was also up-regulation (mRNA) of cytosolic ascorbate peroxidase and down-regulation (mRNA) of SS, homoglutathione synthetase, and bacterial catalase A. Drought stress did not affect nifH mRNA level or leghemoglobin expression, but decreased MoFe- and Fe-proteins. Rewate...
Research Interests: Biochemistry, Carbon, Biology, Drought Stress, Medicine, and 15 moreBiological Sciences, Antioxidants, Antioxidant, Plant, Catalase, Lipid peroxidation, Nitrogenase, Carbohydrate metabolism, Oxidative Damage, Carbon Metabolism, Glutathione Reductase, Leghemoglobin, Leaf water potential, Ascorbate Peroxidase, and Medicago sativa
Phytochelatin synthases (PCS) catalyze phytochelatin (PC) synthesis from glutathione (GSH) in the presence of certain metals. The resulting PC-metal complexes are transported into the vacuole, avoiding toxic effects on metabolism. Legumes... more
Phytochelatin synthases (PCS) catalyze phytochelatin (PC) synthesis from glutathione (GSH) in the presence of certain metals. The resulting PC-metal complexes are transported into the vacuole, avoiding toxic effects on metabolism. Legumes have the unique capacity to partially or completely replace GSH by homoglutathione (hGSH) and PCs by homophytochelatins (hPCs). However, the synthesis of hPCs has received little attention. A search for PCS genes in the model legume Lotus (Lotus japonicus) resulted in the isolation of a cDNA clone encoding a protein (LjPCS1) highly homologous to a previously reported homophytochelatin synthase (hPCS) of Glycine max (GmhPCS1). Recombinant LjPCS1 and Arabidopsis (Arabidopsis thaliana) PCS1 (AtPCS1) were affinity purified and their polyhistidine-tags removed. AtPCS1 catalyzed hPC synthesis from hGSH alone at even higher rates than did LjPCS1, indicating that GmhPCS1 is not a genuine hPCS and that a low ratio of hPC to PC synthesis is an inherent featu...
Research Interests: Biochemistry, Biology, Medicine, Arabidopsis thaliana, Biological Sciences, and 15 morePhylogeny, Plant Physiology, Heavy metals, Lotus, Plant, Glutathione, Arabidopsis, Enzyme, Protein Sequence Analysis, Soybeans, Substrate Specificity, Glycine, Recombinant Proteins, PLANT PROTEINS, and Lotus japonicus
Research Interests:
Ascorbic acid (vitamin C) is a major antioxidant and redox buffer, but is also involved in other critical processes of plants. Recently, the hypothesis has been proposed that legume nodules are unable to synthesize ascorbate and have to... more
Ascorbic acid (vitamin C) is a major antioxidant and redox buffer, but is also involved in other critical processes of plants. Recently, the hypothesis has been proposed that legume nodules are unable to synthesize ascorbate and have to import it from the shoot or root, thus providing a means by which the plant regulates nodule senescence. The last step of ascorbate biosynthesis in plants is catalyzed by l-galactono-1,4-lactone dehydrogenase (GalLDH). The mRNAs encoding GalLDH and three other enzymes involved in ascorbate biosynthesis are clearly detectable in nodules. Furthermore, an active membrane-bound GalLDH enzyme is present in nodule mitochondria. Biochemical assays on dissected nodules reveal that GalLDH activity and ascorbate are correlated in nodule tissues and predominantly localized in the infected zone, with lower levels of both parameters (relative to the infected tissues) in the apex (87%) and senescent region (43%) of indeterminate nodules and in the peripheral tissu...
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Research Interests: Biochemistry, Molecular Biology, Biology, Medicine, Biological Sciences, and 15 moreAntioxidants, Plant Physiology, Nitric oxide, Rhizobium, Plant, Glutathione, Cellular Respiration, Glutathione Peroxidase, Hydrogen Peroxide, Ascorbic Acid, Fabaceae, Rhizobia, Legume, Alternative Oxidase, and Ascorbate Peroxidase
The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medicago sativa L. × Sinorhizobium meliloti 102F78) of the elite genotype N4 and three derived transgenic lines have been studied in detail.... more
The antioxidant composition and relative water stress tolerance of nodulated alfalfa plants (Medicago sativa L. × Sinorhizobium meliloti 102F78) of the elite genotype N4 and three derived transgenic lines have been studied in detail. These transgenic lines overproduced, respectively, Mn‐containing superoxide dismutase (SOD) in the mitochondria of leaves and nodules, MnSOD in the chloroplasts, and FeSOD in the chloroplasts. In general for all lines, water stress caused moderate decreases in MnSOD and FeSOD activities in both leaves and nodules, but had distinct tissue‐dependent effects on the activities of the peroxide‐scavenging enzymes. During water stress, with a few exceptions, ascorbate peroxidase and catalase activities increased moderately in leaves but decreased in nodules. At mild water stress, transgenic lines showed, on average, 20% higher photosynthetic activity than the parental line, which suggests a superior tolerance of transgenic plants under these conditions. Howeve...
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The thiol tripeptide glutathione (GSH; γGlu‐Cys‐Gly) is very abundant in legume nodules where it performs multiple functions that are critical for optimal nitrogen fixation. Some legume nodules contain another tripeptide, homoglutathione... more
The thiol tripeptide glutathione (GSH; γGlu‐Cys‐Gly) is very abundant in legume nodules where it performs multiple functions that are critical for optimal nitrogen fixation. Some legume nodules contain another tripeptide, homoglutathione (hGSH; γGlu‐Cys‐βAla), in addition to or instead of GSH. We have isolated from a pea (Pisum sativum L.) nodule library a cDNA, GSHS2, that is expressed in nodules but not in leaves. This cDNA was overexpressed in insect cells and its protein product was identified as a highly active and specific hGSH synthetase. The enzyme, the first of this type to be completely purified, is predicted to be a homodimeric cytosolic protein. It shows a specific activity of 3400 nmol hGSH min−1 mg−1 protein with a standard substrate concentration (5 mM β‐alanine) and Km values of 1.9 mM for β‐alanine and 104 mM for glycine. The specificity constant (Vmax/Km) shows that the pure enzyme is 57.3‐fold more specific for β‐alanine than for glycine. Southern blot analysis re...
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Research Interests:
The thiol tripeptides, glutathione (GSH) and homoglu-tathione (hGSH), perform multiple roles in legumes, including protection against toxicity of free radicals and heavy metals. The three genes involved in the synthesis of GSH and hGSH in... more
The thiol tripeptides, glutathione (GSH) and homoglu-tathione (hGSH), perform multiple roles in legumes, including protection against toxicity of free radicals and heavy metals. The three genes involved in the synthesis of GSH and hGSH in the model legume, Lotus japonicus, have been fully characterized and appear to be present as single copies in the genome. The γ-glutamylcysteine synthetase (γecs) gene was mapped on the long arm of chromosome 4 (70.0 centimorgans [cM]) and consists of 15 exons, whereas the glutathione synthetase (gshs) and homoglutathione synthetase (hgshs) genes were mapped on the long arm of chromosome 1 (81.3 cM) and found to be arranged in tandem with a separation of approximately 8 kb. Both genes consist of 12 exons of exactly the same size (except exon 1, which is similar). Two types of transcripts were detected for the gshs gene, which putatively encode proteins localized in the plastids and cytosol. Promoter regions contain cis-acting regulatory elements th...
Research Interests: Genetics, Microbiology, Chemistry, Plant Biology, Biology, and 14 morePlant Molecular Biology, Medicine, Phylogeny, Lotus, Glutathione, Gene, Molecular Plant Microbe Interactions, Fabaceae, Base Sequence, Exon, Glutamate Cysteine Ligase, Molecular Sequence Data, Lotus japonicus, and reverse transcriptase polymerase chain reaction
Research Interests:
Research Interests: Plant Biology, Biology, Cell Biology, Medicine, Gene Silencing, and 15 moreRNA interference, Rhizobium, Experimental Botany, Polymerase Chain Reaction, Reverse genetics, Genetic transformation, Gene, Plant Roots, Arabidopsis, Medicago, Gene Function, Base Sequence, Agrobacterium, Lateral Root, and Restriction Mapping
Research Interests:
The thiol tripeptides, glutathione (GSH) and homoglu-tathione (hGSH), perform multiple roles in legumes, includ-ing protection against toxicity of free radicals and heavy met-als. The three genes involved in the synthesis of GSH and hGSH... more
The thiol tripeptides, glutathione (GSH) and homoglu-tathione (hGSH), perform multiple roles in legumes, includ-ing protection against toxicity of free radicals and heavy met-als. The three genes involved in the synthesis of GSH and hGSH in the model legume, Lotus japonicus, ...