Leghemoglobin

Abstract: The role of nitrogen metabolism in the survival of prolonged periods of waterlogging was investigated in highly flood-tolerant, nodulated Lotus japonicus plants. Alanine production revealed to be a critical hypoxic pathway. Alanine is the only amino acid whose biosynthesis is not inhibited by nitrogen deficiency resulting from RNA interference silencing of nodular leghemoglobin. The metabolic changes that were induced following waterlogging can be best explained by the activation of alanine metabolism in combination with the modular operation of a split tricarboxylic acid pathway. The sum result of this metabolic scenario is the accumulation of alanine and succinate and the production of extra ATP under hypoxia. The importance of alanine metabolism is discussed with respect to its ability to regulate the level of pyruvate, and this and all other changes are discussed in the context of current models concerning the regulation of plant metabolism.

Abstract: A. General Introduction.- The Historical Background of the Bacteria-Plant Interaction.- The Rhizobium-Plant Interaction.- La Piste des Opines.- B. The Rhizobium-Plant Interaction.- I. The Rhizobium meliloti-Medicago sativa System.- Studies on Rhizobium meliloti Plasmids and on Their Role in the Control of Nodule Formation and Nitrogen Fixation: The pSym Megaplasmids and the Other Large Plasmids.- Studies on Rhizobium meliloti Plasmids and on Their Role in the Control of Nodule Formation and Nitrogen Fixation: A Strategy for Region-Specific Transposon Mutagenesis of pSym Megaplasmid.- Analysis of Symbiotic Nitrogen Fixation Genes Carried by the Rhizobium meliloti Mega-Plasmid.- Characterization of Rhizobium meliloti Genetic Loci Essential for Symbiotic Nitrogen Fixation.- Mapping and Regulation of the Structural Genes nifK, nifD, and nifH of Rhizobium meliloti.- Early Nodulation Genes of Rhizobium meliloti.- Symbiotic Nitrogen Fixation Genes of Rhizobium meliloti.- Vector Plasmids for in-Vivo and in-Vitro Manipulations of Gram-Negative Bacteria.- II. The Rhizobium leguminosarum-Pisum sativum System.- Genetic Analysis of pRL1 JI, a Symbiotic Plasmid of Rhizobium leguminosarum.- Natural Variation in Rhizobium Plasmids.- Analysis of Nodule-Specific Plant and Bacteroid Proteins in Pea Plants Inoculated by Transposon Mutagenized Rhizobium leguminosarum.- III. The Rhizobium japonicum-Glycine max System.- Rhizobia Use Free-Living N2 Fixation to Promote Growth by a Mechanism of Crossfeeding.- The Nitrogenase Genes of Rhizobium japonicum.- The Structure and Organization of the Soybean Leghemoglobin Genes.- The Role of Plant Genes in Soybean-Rhizobium Interactions.- IV. The Interaction of Different Rhizobium Species with Plants.- General Organization of Nitrogen Fixation Genes in Rhizobium phaseoli.- Identification of Nitrogen Fixation and Nodulation Genes on a Large Plasmid from a Broad Host Range Rhizobium sp..- Identification, Broad Host Range Mobilization and Mutagenesis of a Rhizobium trifolii Sym::R68.45 Cointegrate Plasmid.- Genetic Analysis of the Symbiotic Regions in Rhizobium trifolii and Rhizobium parasponia.- Molecular Anatomy of the Symbiotic Region in Rhizobium trifolii and Rhizobium parasponia.- Stem Nodulation in Aeschynomene: A Model System for Bacterium-Plant Interactions.- C. The Agrobacterium-Plant Interaction.- I. The Tumor-Inducing Plasmids of Agrobacterium.- Onc- and vir-Genes Located on the Ti-Plasmid of Agrobacterium tumefaciens.- Plasmid Genes Essential for the Interactions of Agrobacteria and Rhizobia with Plant Cells.- Genetic Analysis of Host Range Expression by Agrobacterium.- The Biology of Genetic Transformation of Higher Plants by Agrobacterium rhizogenes.- Expression of the T-Region of Octopine Plasmid pTi Ach5 into Protein in Bacterial Systems.- II. The Role of T-DNA in Transformed Plant Cells.- Liposomes as a Carrier of Ti Plasmid into Protoplasts.- Plant Protoplast Transformation by Agrobacterium tumefaciens and its Ti Plasmid DNA.- The Study of Integration of Tumor-Inducing DNA from the Nopaline Ti Plasmid of Agrobacterium tumefaciens.- Transcription of the Ti-Plasmid in Crown Gall Tumors.- TR Genes Involved in Agropine Production.- Transcription of T-DNA in Octopine and Nopaline Crown Gall Tumours.- Genetic Analysis of T-DNA and Regeneration of Transformed Plants.- D. Plant Pathogenic Bacteria and Related Aspects.- The Genetics of the Cherry Pathogen, Pseudomonas syringae pathovar morsprunorum.- Towards the Genetical Analysis of Pathogenicity of Xanthomonas campestris.- Molecular Analysis of Virulence Genes in Pseudomonas solanacearum.- Cloning of Genes Involved in Bacterial Ice Nucleation and Fluorescent Pigment/Siderophore Production.- The Genetics of Indoleacetic Acid Production and Virulence in Pseudomonas savastanoi.- Azospirillum Genetics.- Genome Rearrangement of the Rhizobiaceae.

Abstract: We cloned two hemoglobin genes from Arabidopsis thaliana. One gene, AHB1, is related in sequence to the family of nonsymbiotic hemoglobin genes previously identified in a number of plant species (class 1). The second hemoglobin gene, AHB2, represents a class of nonsymbiotic hemoglobin (class 2) related in sequence to the symbiotic hemoglobin genes of legumes and Casuarina. The properties of these two hemoglobins suggest that the two families of nonsymbiotic hemoglobins may differ in function from each other and from the symbiotic hemoglobins. AHB1 is induced, in both roots and rosette leaves, by low oxygen levels. Recombinant AHB1 has an oxygen affinity so high as to make it unlikely to function as an oxygen transporter. AHB2 is expressed at a low level in rosette leaves and is low temperature-inducible. AHB2 protein has a lower affinity for oxygen than AHB1 but is similar to AHB1 in having an unusually low, pH-sensitive oxygen off-rate.

Abstract: 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. Rewatering of plants led to a partial recovery of the activity (75%) and proteins (>64%) of N2ase, a complete recovery of Suc, and a decrease of malate (−48%) relative to control. The increase in O2 diffusion resistance, the decrease in N2ase-linked respiration and N2ase proteins, the accumulation of respiratory substrates and oxidized lipids and proteins, and the up-regulation of antioxidant genes reveal that bacteroids have their respiratory activity impaired and that oxidative stress occurs in nodules under drought conditions prior to any detectable effect on SS or leghemoglobin. We conclude that a limitation in metabolic capacity of bacteroids and oxidative damage of cellular components are contributing factors to the inhibition of N2ase activity in alfalfa nodules.