George Ignatov

Effects of Succinate on Manganese Toxicity in Pea Plants

ABSTRACT Pea (Pisum sativum cv. Citrine) plants were grown in nutrient solution containing various manganese (Mn) concentrations in the presence or absence of succinate to evaluate the potential role of succinate in the plant tolerance to Mn excess. Supplying pea plants with excess Mn led to a reduction in the relative growth rate (RGR), chlorophyll a and b content, photosynthetic O2 evolution activity, and photosystem II (PSII) activity, as measured in the light-adapted state (φPSII) in comparison to the control. The primary photochemical efficiency of PSII, estimated by the Fv/Fm ratio, was less affected by increasing Mn concentration. Chloroplasts from Mn-treated leaves exhibited significant changes in their ultrastructure, depending on the strength of Mn toxicity. The concentration of Mn in roots, stem, and leaves increased with the increase of Mn in the nutrient solution. Addition of succinate before and after Mn treatment did not reduce the inhibitory effect of Mn on the plant growth, chlorophyll fluorescence parameters, photosynthetic O2 evolution activity, and chloroplast structure of the pea plants. It was found that supply of exogenous succinate at a high Mn concentration (over 1500 μM) in the nutrient solution led to an increase of Mn uptake in the roots accompanied by a decrease in a Mn translocation to the leaves and stems compared to Mn-treated pea-plants. However, differences in the toxicity effect of Mn in both Mn and Mn/Succinate-treated pea plants were not detected. Thus, such changes in Mn distribution within the Mn/succinate-treated plant did not confer tolerance of Mn excess to pea plants. These results suggest that succinate probably has an affinity for Mn and may function as a “terminal acceptor” of large amounts of Mn, decreasing Mn transport to the stem and leaves, but does not contribute to Mn tolerance.

Effect of low pH on nitrogen fixation of common bean grown at various calcium and nitrate levels

Abstract The influence of low pH (4.0–4.5) of the medium on nodulation, nodule biomass, nodule nitrogenase activity, and ultrastructure at various concentrations of calcium (Ca) (0.127 mM and 0.508 mM) and nitrate (NO3) (0.390 mM and 1.560 mM) at different stages of development (2nd, 3rd, 6th, and 7th compound leaf) of the common bean plants was studied. The experiment was conducted using Hellriegels nutrient solution under greenhouse conditions. Bean root nodule nitrogen (N2) fixation was influenced favorably at a decrease of Ca (0.127 mM) and NO3 (0.390 mM) concentrations in the growth solution. In contrast, the biomass of the roots, stems, leaves, and pods decreased at low Ca and NO3 levels while the most sensitive were the leaves and pods of the plants. The number of nodules, their fresh and dry weight, nitrogenase activity, and ultrastructure was affected to a greater extent at a low pH of the medium when Ca and NO3 concentrations were low (0.127 mM and 0.390 mM, respectively). Under these condition...

Polyamine-induced changes in symbiotic parameters of the Galega orientalis-Rhizobium galegae nitrogen-fixing system

Plants of goats rue (Galega orientalis) inoculated with Rhizobium galegae strain HAMBI 540 were grown in the presence of putrescine (Put), spermidine (Spd) or spermine (Spm), and several symbiotic characteristics were investigated to delineate the influence of polyamines (PA) on this nitrogen-fixing system. All three PA exerted a concentration-dependent effect on the nodule parameters tested. The increment of nodulation ability and nodule biomass accumulation was extreme (from 2.4- to 4.0-fold) when plants were subjected to 10 and 50 μM of various PA. However, at 100 μM a negative effect was observed. The acetylene-reduction activity of nodulated roots was increased also in response to treatment with the lower PA concentrations. The level of nitrogenase activity supported by succinate was significantly higher in bacteroids isolated from PA-treated nodules than in bacteroids from control nodules. The symbiotic parameters were also dependent on the type of PA used; the most effective being the diamine Put, while Spm showed a smaller physiological effect with respect to the others. Polyamines altered the ultrastructure of Galega nodule infected cells. After treatment with these substances, pronounced changes in the relative volume of the main components of infected cells and their compartments were observed. The significance of the structural observations and morphometric analyses, their relationship to differences in nitrogen fixation and possible modes of action are discussed.

Remedying the iron-deficient maize plants by new synthetic macromolecular chelating agents

The efficacy of Fe3+ complexes of polyethers with 8-quinolinol (8QOH) chelating groups attached to the polymer chain at different positions of the aromatic ring or having different chain length for remedying the iron-deficient maize plants was evaluated. The efficacy of chelates of polymers having terminal 8QOH residues was compared with that of complexes of ethylenediaminetetraacetic acid, 8QOH, mixtures of commercial polyethers with isopropylamino end-groups and 8QOH or FeCl3.6H2O. It was found that at 30/25 °C (day/night) and photosynthetic photon flux density 1100–1300 μmol m−2 s−1, the chlorotic maize plants recovered for 4 days of iron re-supply. An increase in the fresh and dry weight, leaf area, net photosynthetic CO2 uptake of maize leaves, leaf pigment composition and chlorophyll fluorescence was more pronounced in the plants supplied with Fe3+ chelates of polymers bearing 8QOH groups attached at 5-position, compared to the other tested Fe3+complexes. The importance of the stability of Fe3+ complexes, structure of the chelating agent and the necessity of effective ligand exchange between synthetic chelators and free phytosiderophore in iron uptake by strategy II plants was discussed.

Polyethers with 8-Hydroxy-54-Quinolinyl Chelating End-Groups: Effect on Iron Nutrition of Plants and Antibacterial/Antimycotic Effects

The effect of Fe3+ chelates of polyethers having terminal 8-quinolinol (8Q) residues linked to the polymer chain at different ring positions on the remedy of iron-deficient maize plants was studied. It was found that Fe3+ chelates of polymers with 8Q groups attached at the 5-position (HOQ-P-QOH) were the most effective. Decreasing the temperature and photosynthetic photon flux density caused a four-fold retardation in the remedy of iron-deficient plants. The results are explained in terms of the stability of the Fe3+ complexes. The microbiological tests showed that the polyethers were active against Gram-positive and Gram-negative bacteria. HOQ-P-QOH also exhibited antimycotic activity.

Effect of high nitrate concentrations on dicarboxylate transport across the peribacteroid membrane of soybean root nodules

Summary Uptake studies were carried out with intact peribacteroid units isolated from nodules of soybean plants ( Glycine max L. cv. Hodgson) inoculated with Bradyrhizobium japonicum strain 273 and treated for 48h with high concentrations of nitrate. Malate penetrated the peribacteroid membrane most rapidly when the plants were affected by 0.390 mM nitrate. The 2 mM nitrate treatment had a slightly negative effect on the malate uptake, resulting in a 12 % decrease in the dicarboxylate transport across the peribacteroid membrane, as compared with the controls. Malate transport across the peribacteroid membrane decreased by 55% after 7.5 mM nitrate treatment and by 85% after 15 mM nitrate treatment. At higher nitrate levels poly-β-hydroxybutyrate synthesis was increased. These data support the suggestion that in these conditions malate is funneled to poly-s-hydroxybutyrate synthesis, which together with the reduced malate uptake by peribacteroid units could explain the inhibited nitrogen fixation.

Role of Ca2+ in Bradyrhizobium japonicum Strain 273 Attachment Ability and Accumulation on Soybean Root Surface

Summary Ca2+ limitation in the cultivation medium of Bradyrbizobium japonicum strain 273 and in Hellriegels nutrient solution led to optimal bacterial growth and to greater accumulation and attachment of the bacterium to the root hair surface. With the increase of Ca2+ in the medium the bacterial attachment ability and their quantity on the root surface were reduced. Optimal nodule formation in soybean plants required 127 µM Ca2+ in the nutrient medium. The problem concerning differences between Bradyrbizobium japonicum and Rhizobium leguminosarum attachment and accumulation caused by Ca2+ is discussed.

Remedying the iron-deficient maize plants grown at lower than the optimal temperature and irradiance by new synthetic macromolecular iron-chelating agents

Summary The efficacy of Fe 3+ complexes of polyethers having chelating terminal 8-quinolinol (8QOH) residues for remedying the iron-deficient maize plants at temperatures of 20/16°C and photosynthetic photon flux density (PPFD) 500-600 μmol m -2 s -1 was evaluated by their effect on the fresh and dry weight, pigment content (total chlorophyll and carotenoids), chlorophyll fluorescence, and photosynthetic activity of maize plants. In order to estimate the effect of the oligomer nature of the polyethers with 8QOH group attached to the oxyethylene chain at different positions of aromatic ring, tests on chlorotic plants were also performed with Fe 3+ complexes of low-molecular-weight ligand 8QOH, and mixtures of commercial polyethers with isopropylamino end-groups (Jeffamines ED) and 8QOH (Jeff/8QOH). The efficacy of Fe 3+ chelates of synthetic chelator ethylenediaminetetraacetic acid and FeCl 3 · 6H 2 O for remedying the chlorotic maize plants under the same conditions was also tested. At temperatures of 20/16 °C and PPFD 500-600 1J.mol m-2 s-1 , the Fe3+ chelates of polymers with 8QOH groups attached at 5-position were the most effective for remedying the iron-deficient maize plants compared to the other tested Fe 3+ complexes. It was found that the plant remedy process was sensitive to lowering of the temperature and PPFD. The remedy of chlorotic maize plants supplied with investigated Fe 3+ complexes at 20/16 °C (day/night) and PPFD 500-600 μmol m -2 s -1 retarded 4-fold compared to that observed at 30/25 °C and PPFD 1100-1300 μmol m -2 s -1 . We concluded that the longer period for remedying the iron-deficient maize plants at lower than the optimal temperature and PPFD is probably due to the fact that, under these conditions, the amount of DMA released from roots is several times lower, and the efficiency of the high-affinity system for uptake of Fe 3+ -PS is decreased as compared to that at optimal temperature and PPFD.

Free-living and symbiotic characteristics of plasmid-cured derivatives of Rhizobium galegae

Rhizobium galegae strain NBIMTC2250 contains two plasmids one of which (the larger one) is the symbiotic plasmid. To determine the participation of the smaller plasmid in cellular functions and in the symbiosis, we used a positive selection system for isolation of derivatives cured of this plasmid. The derivatives did not show differences from the wild type with respect to the following free-living cellular properties: antibiotic-resistance pattern, carbohydrates and organic acid utilization, growth rate and colony morphology in pure culture, lipopolysaccharide (LPS) profile, motility and sensitivity to extreme temperatures, which indicated that these functions were not plasmid encoded. Some of the cured derivatives differed from the wild type in the symbiotic characteristics, and the possible reason for the differences was discussed. In these cases reintroduction of the plasmid did not restore the derivatives to a wild type but the plasmid-free and plasmid-recontaining derivatives had similar symbiotic phenotype. Hybridization study showed that the smaller plasmid had been lost integrally in all cured derivatives. These results and the fact that almost half of the plasmid-cured derivatives have the symbiotic characteristics similar to those of the parent strain suggested that the smaller plasmid of strain Rhizobium galegae NBIMTC2250 did not participate in the symbiotically important functions of this strain.