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At least 811 records · Page 45Linked to original sources
PubMed1978

Interdependence of Nitrogen Nutrition and Photosynthesis in Pisum sativum L: II. Host Plant Response to Nitrogen Fixation by Rhizobium Strains.

Physiological responses to infection by strains of Rhizobium leguminosarum which differed in their capacity to reduce N(2) were determined in 26-day-old pea plants (Pisum sativum L. cv. Alaska) grown under uniform environmental conditions in the absence of combined N. The highest N(2) reduction rates, calculated from H(2) evolution and C(2)H(2)-dependent C(2)H(4) production measurements, were approximately 6-fold greater than the lowest. Higher N(2) fixation rates were associated with greater CO(2) exchange rates (R(2) = 0.92) and carboxylation efficiency (R(2) = 0.99). Increases in the apparent relative efficiency of N(2) fixation [1-(H(2) evolved in air/C(2)H(2) reduced)] (acteroid efficiency) were associated with increases in whole-plant N(2) fixation efficiency (N(2)/CO(2) reduction ratio) (R(2) = 0.95). Whole-plant dry weight and total N content were related by regression analysis (R(2) = 0.98); both parameters were enhanced by increased N(2) fixation in a manner analogous to previously reported increases caused by greater external applications of NH(4) (+). These data reveal that photosynthetic parameters in genetically uniform host plants grown under identical environmental conditions are affected by N(2) fixation characteristics of the rhizobial symbiont. The measured efficiencies of micro- and macrosymbiont are directly related under uniform environments.

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PubMed1985

Nitrogen nutrition and metabolic interconversions of nitrogenous solutes in developing cowpea fruits.

Budgets for import and utilization of ureide, amides, and a range of amino acids were constructed for the developing first-formed fruit of symbiotically dependent cowpea (Vigna unguiculata [L.] Walp. cv Vita 3). Data on fruit total N economy, and analyses of the xylem and phloem streams serving the fruit, were used to predict the input of various solutes while the compositions of the soluble and protein pools of pod, seed coat, and embryo were used to estimate the net consumption of compounds. Ureides and amides provided virtually all of the fruit's N requirements for net synthesis of amino compounds supplied inadequately from the parent plant. Xylem was the principal source of ureide to the pod, while phloem was the major source of amides to pod and seed. All fruit parts showed in vitro activity of urease (EC 3.5.1.5), allantoinase (EC 3.5.2.5), asparaginase (EC 3.5.11), ammonia-assimilating enzymes and aspartate and alanine aminotransferases (EC 2.61.1 and EC 2.6.1.1.2). Asparagine:pyruvate aminotransferase (EC 2.6.1.14) was recovered only from the pod. The pod was initially the major site for processing and incorporating N; later seed coats and finally embryos became predominant. Ureides were broken down mainly in the pod and seed coat. Amide metabolism occurred in all fruit organs, but principally in the embryo during much of seed growth. Seed coats released N to embryos mainly as histidine, arginine, glutamine, and asparagine, hardly at all as ureide. Amino compounds delivered in noticeably deficient amounts to the fruit were arginine, histidine, glycine, glutamate, and aspartate, while seeds received insufficient arginine, histidine, serine, glycine, and alanine. Quantitatively based schemes are proposed depicting the principal metabolic transformation accompanying N-flow between seed compartments during development.

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PubMed1986

Effects of nitrogen dioxide and nitrate nutrition on nodulation, nitrogenase activity, growth, and nitrogen content of bean.

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO(2) (0-0.5 parts per million) on nodulation and in vivo acetylene reduction activity of the roots and on growth and nitrate and Kjeldahl N concentration in shoots was studied in bean (Phaseolus vulgaris L. cv Kinghorn Wax) plants. Exposing 8-day old seedlings for 6 hours each day, for 15 days, to 0.02 to 0.5 parts per million NO(2) decreased total nodule weight at 0 and 1 millimolar nitrate, and nitrogenase (acetylene reduction) activity at all concentrations of nitrate. The pollutant had little effect on root fresh or dry weights. Shoot growth was inhibited by NO(2). The NO(2) exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO(2) markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO(2) concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants.

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PubMed1991

Effects of genetically engineered microorganisms on nitrogen transformations and nitrogen-transforming microbial populations in soil.

The principal concern about releasing genetically engineered microorganisms (GEMs) into the environment is their potential adverse effects on the environment, whether caused directly or indirectly by the GEMs. The effects of five GEMs on ammonification, nitrification, and denitrification in soil were studied. With the possible exception of a strain of Enterobacter cloacae carrying a plasmid, no consistent statistically or ecologically significant differences in effects on these processes or on the population dynamics of the microorganisms responsible for the processes were observed between soils inoculated with the GEMs or their homologous plasmidless hosts and those that were not inoculated. Increasing the concentration of montmorillonite in the soil enhanced the rate of nitrification, regardless of the inoculum, indicating that the perfusion technique used was sensitive enough to detect changes in nitrification rates when they occurred.

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