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D L Eskew

Publications and source records attributed to D L Eskew.

9 recordsLinked to original sources
PubMed1993

DNA amplification fingerprinting of the Azolla-Anabaena symbiosis.

The Azolla-Anabaena symbiosis has been used for centuries as a nitrogen biofertilizer in rice paddies. Genetic improvement of the symbiosis has been limited by the difficulty in identifying Azolla-Anabaena accessions and Anabaena azollae strains. The recently developed technique of DNA amplification fingerprinting (DAF) was applied to this problem. DAF uses single, short, oligonucleotide primers of arbitrary sequence to direct amplification of a characteristic set of DNA products by a thermostable DNA polymerase in a thermocycling reaction. The products are separated in polyacrylamide gels and detected by silver staining. DAF could easily distinguish and positively identify accessions of Azolla-Anabaena with DNA extracted from the intact symbiosis. The contribution of prokaryotic Anabaena sequences to the fingerprint of the intact symbiosis, however, ranged from 0 to 77%, depending on the primer sequence. Therefore, DNA extracted from the intact symbiosis would not be suitable for Azolla taxonomy studies. The fingerprints of Anabaena strains isolated by sucrose gradient centrifugation from different species of Azolla could be easily distinguished, and DAF patterns were used to confirm the maternal pattern of transmission of Anabaena in a sexual hybrid. Template DNA extracted from roots was used to produce fingerprints for Azolla without interference from the microsymbiont. Comparison of the patterns from the parents and a hybrid gave strong evidence confirming sexual hybridization.

Anabaena↗
PubMed1984

A simple plant nutrient solution purification method for effective removal of trace metals using controlled pore glass-8-hydroxyquinoline chelation column chromatography.

Column chelation chromatography on controlled pore glass-8-hydroxyquinoline was demonstrated to be a very efficient method for removing trace metal contaminants from concentrated macronutrient salt solutions used to prepare nutrient media. By using (63)Ni and (65)Zn radio-isotopes as tracers, controlled pore glass-8-hydroxyquinoline column packings were found to retain 99.9% of the radiotracer and quantitative recovery of the radioisotopes from these columns was obtained by eluting with 1.2 n HCl. This method has several advantages over liquid-liquid extraction methods of purification which previously have been used in plant micronutrient research.

Journal Article↗
PubMed1984

Nickel in higher plants: further evidence for an essential role.

Soybeans (Glycine max [L.] Merr.) grown in Ni-deficient nutrient solutions accumulated toxic urea concentrations which resulted in necrosis of their leaflet tips, a characteristic of Ni deficiency. Estimates of the Ni requirement of a plant were made by using seeds produced with different initial Ni contents. When compared to soybeans grown from seeds containing 2.5 nanograms Ni, plants grown from seeds containing 13 nanograms Ni had a significantly reduced incidence of leaflet tip necrosis. Plants grown from seeds containing 160 nanograms Ni produced leaves with almost no leaflet tip necrosis symptoms. Neither Al, Cd, Sn, nor V were able to substitute for Ni.In other experiments, a small excess of EDTA was included in the nutrient solution in addition to that needed to chelate micronutrient metals. Under these conditions, nodulated nitrogen-fixing soybeans had a high incidence of leaflet tip necrosis, even when 1 micromolar NiEDTA was supplied. However, in nutrient solutions containing inorganic sources of N, 1 micromolar NiEDTA almost completely prevented leaflet tip necrosis, although no significant increase in leaf urease activity was observed. Cowpeas (Vigna unguiculata [L.] Walp) grown in Ni-deficient nutrient solutions containing NO(3) and NH(4) also developed leaflet tip necrosis, which was analogous to that produced in soybeans, and 1 micromolar NiEDTA additions prevented these symptoms.These findings further support our contention that Ni is an essential element for higher plants.

Journal Article↗
PubMed1983

Nickel is not required for apourease synthesis in soybean seeds.

Soybeans (Glycine max L. Merr. cv ;Maple Presto') harvested from plants cultured in nickel-free medium had <0.005% the activity of nickel-sufficient beans and only 15% the activity of a urease-null variety, Itachi. However, whereas Itachi has no detectable urease protein, nickel-free beans of the variety Maple Presto exhibit normal or near normal levels of urease apoprotein. Thus, nickel isn't necessary for urease apoprotein synthesis. The apoprotein wasn't activated by nickel in vitro but, upon seed imbibition of nickel, urease was partially activated. This in vivo activation was not inhibited by cychoheximide.

Journal Article↗
PubMed1981

Heterotrophic n(2) fixation and distribution of newly fixed nitrogen in a rice-flooded soil system.

Rice (Oryza sativa L.) plants growing in pots of flooded soil were exposed to a (15)N(2)-enriched atmosphere for 3 to 13 days in a gas-tight chamber. The floodwater and soil surface were shaded with a black cloth to reduce the activity of phototrophic N(2)-fixing micro-organisms. The highest (15)N enrichments were consistently observed in the roots, although the total quantity of (15)N incorporated into the soil was much greater. The rate of (15)N incorporation into roots was much higher at the heading than at the tillering stage of growth. Definite enrichments were also found in the basal node and in the lower outer leaf sheath fractions after 3 days of exposure at the heading stage. Thirteen days was the shortest time period in which definite (15)N enrichment was observed in the leaves and panicle. When plants were exposed to (15)N(2) for 13 days just before heading and then allowed to mature in a normal atmosphere, 11.3% of the total (15)N in the system was found in the panicles, 2.3% in the roots, and 80.7% in the subsurface soil. These results provide direct evidence of heterotrophic N(2) fixation associated with rice roots and the flooded soil and demonstrate that part of the newly fixed N is available to the plant.

Journal Article↗
PubMed1978

Denitrification in Rhizobium.

Thirty-three strains of Rhizobium were examined for their reduction of nitrate under anoxic conditions. Three patterns of dissimilatory nitrate reduction were observed: (1) reduction to N2O and N2 (denitrification), (2) reduction to and subsequent accumulation of NO2- (nitrate respiration), (3) no reduction. Strains of R. japonicum and the cowpea miscellany displayed all three types, while strains of R. leguminosarum, R. phaseoli, and R. trifolii did not reduce nitrate by dissimilatory means. The production and subsequent metabolism of N2O was considerably different among the denitrifying strains: in some instances, N2O was a transient intermediate, while in others, it continued to accumulate during the incubation period.

Anaerobiosis↗
PubMed1977

Nitrogen fixation, denitrification, and pleomorphic growth in a highly pigmented Spirillum lipoferum.

A strain of Spirillum lipoferum with intense red pigmentation was isolated from the roots of Cynodon dactylon "Coastal." This isolate vigorously reduced acetylene when grown in N-free, Na-malate, semisolid agar, and it was identical to S. lipoferum strain SP7 by standard taxonomic tests. Both S. lipoferum SP7 and the C. dactylon root isolate displayed the unique features of being denitrifiers as well as N2 fixers. The N2-dependent growth curve was biphasic: cells in younger cultures showed the characteristic spiral shape and motility, but those in older cultures developed larger, nonmotile, cystlike forms. Nitrogenase activity seemed associated only with younger spiral forms. The red pigment may be a b- or c-type cytochrome. The strong red color, which this strain develops, could be used as a marker in evaluating soil inoculation experiments.

Acetylene↗
PubMed1977

Effect of rj1rj1 (non-nodulating) soybeans on nodulation of near isogenic Rj1Rj1 plants in nutrient culture.

An earlier proposal (Can. J. Microbiol. 7: 851; 1961) that rj1rj1 (non-nodulating) soybeans (Glycine max (L.) Merr.) excrete a substance that inhibits nodulation of Rj1 Rj1 (nodulating) plants was tested. Using near isogenic lines (isolines) of "Clark" and "Harosoy" soybeans, we consistently found nonsignificant reduction in nodule number and acetylene reduction per Rj1Rj1 plant grown in association with their rj1rj1 counterparts: these results suggest that a nodulation inhibitor is not associated with the rj1 gene. Reducing the number of plants grown in each pot produced significant (P = 0.05) reductions in nodule number per Rj1Rj1 plant, and resembled the observations of the earlier report. On this basis, we suggest that the reported inhibition of nodulation was due to a failure to detoxify or remove an inhibitor (possibly nitrate) already present in the nutrient solution. Both Clark isolines removed nitrate from their nutrient solutions at similar rates. Harosoy rj1rj1 plants removed nitrate at a significantly (P - 0.05) slower rate than Harosoy Rj1Rj1 plants, but the differences were not correlated (P = 0.05) with the small observed decreases in nodulation. These differences in nitrate uptake were highly correlated (P = 0.01) with reduced dry weight per Harosoy rj1rj1 plant.

Acetylene↗