Marie Němcová

Symbiotic dinitrogen fixation as affected by short-term application of nitrate to nodulatedPisum sativum L.

Effect of nitrate on the nitrogenase (C2H2-reduction) activity, growth of nodule tissue accumulation of nitrate and nitrate reductase activity in 4-weeks-old nodulated peas (Pisum sativuml.) was investigated. A relatively slow decrease of the total nitrogenase activity (μmol C2H4 per root per h), as compared with plants cultivated without nitrate, was due to both retardation of further growth of the nodule tissue and to a decrease of their specific nitrogenase activity (μmol C2H4 per gf.wt. per h). However, an absolute and pronounced decrease of both nitrogenase activities occurred only 4 or 7 d after the application of nitrate. The addition of nitrate led to its rapid accumulation in the nodule and leaf tissue with a simultaneous induction of the nitrate reductase activity. The nitrogenase activity was not completely inhibited even after a 7-d cultivation with 280 ppm NO3−-N in the nutrient medium and after accumulation of up to 180 ppm NO3−-Nf.wt. in the nodule tissue. The results obtained indicate that the “photosynthate deprivation” reflects competition between assimilation of nitrate and fixation of dinitrogen.

Relationships between nitrate level, nitrate reductase activity and anaerobic nitrite production inPisum sativum leaf tissue

Anaerobic nitrite production (thein vivo NO3-R activity) in an incubation medium lacking exogenous nitrate but containing 0.5%n-propanol and 0.1% Triton X-100 showed higher correlation (y - axb) with the level of endogenous nitrate inPisum sativum L. leaves than thein vitro nitrate reductase activity. Thein vivo NO3-R activity correlated well with thein vitro activity up to the 50 ppm NO3-N level of endogenous nitrate. The ratioin vivo: in vitro activity slightly decreased with increasing level of endogenous nitrate in leaf tissue.

Comparison of peas nodulated with a hydrogen-uptake positive or negative strain ofRhizobium leguminosarum

During a 49-d growth period peas nodulated with a Hup+ strain ofR. leguminosarum (17-to 66-d-old plants) had a significantly higher total (by 80 %) and specific (by 155 %) C2H2-reducing nitrogenase activity a lower dihydrogen production by the root nodules (by 53 %), and a higher value of the relative efficiency coefficient of nitrogen fixation (by 45 %) in comparison with the plants nodulated with a Hup- strain. The nodules induced by the Hup+ strain evolved less CO2 per unit of the acetylene-reducing activity than those induced by the Hup- strain (by 30 %). However, the accumulation of the nodule dry mass was significantly lower in the plants nodulated with the Hup+ strain.

Comparative response ofPisum sativum nodulated with indigenous soilRhizobium populations and/or co-inoculated with aRhizobium leguminosarum strain

No significant differences in the acetylene-reducing activity and evolution of H2 and CO2 nodulated roots ofPisum sativum inoculated with soilRhizobium populations from two soils with different acidities (Ruzyně soil 7.6; Lukavec soil 4.9) were observed.Rhizobium population from Lukavec soil formed nodules, exhibiting a higher H2 evolution. Co-inoculation with the Hup+ strain 128C30 (7×107 cells per seedling) eliminated, to some extent, the effect of soil populations on physiological activity.No significant differences in the acetylene-reducing activity and evolution of H2 and CO2 nodulated roots ofPisum sativum inoculated with soilRhizobium populations from two soils with different acidities (Ruzyně soil 7.6; Lukavec soil 4.9) were observed.Rhizobium population from Lukavec soil formed nodules, exhibiting a higher H2 evolution. Co-inoculation with the Hup+ strain 128C30 (7×107 cells per seedling) eliminated, to some extent, the effect of soil populations on physiological activity.

Fluctuations of nitrogenase and cytosol glutamine synthetase activity in pea (Pisum sativum L.) nodules in the course of vegetation

Changes in glutamine synthetase activity located in the cytosol of root nodules were followed in pea (Pisum sativum L.) plants in relation to their nitrogenase activity. The highest glutamine synthetase activity was found in young nodules (15 days after inoculation) and its changes in 17-to 45-day-old plants showed a positive correlation with nitrogenase activity. In contrast to nitrogenase activity, changes in glutamine synthetase activity during the day and night period could not be unequivocally interpreted in terms of diurnal fluctuation.

Behaviour of nodulatedPisum sativum L. under short-term nitrate stress conditions

Nitrate (20 mM) applied to the root medium of 28-day-old nodulated pea plants (Pisum sativum L., cv. Jupiter) immediately retarded nodule growth and inhibited root nodulation. Acetylene-reducing and H2-evolving nitrogenase activities were also significantly inhibited. The inhibitory effect of nitrate on nodule respiration was less pronounced while the respiration of roots was increased after the addition of nitrate. The levels of cytosol glutamine synthetase and nitrate reductase in nodule cytosol were permanently decreased from the 4th day after nitrate application. These results indicate that the inhibitory effect of high nitrate concentration on whole nodule metabolism is nonspecific in nature.

Acetylene reduction (dinitrogen fixation) and nitrification in soil as affected by the structural aggregate size.

The effect of size of structural aggregates on the intensity of nitrification and nitrogenase (nitrogen: acetylene oxidoreductase) activity was investigated in three soils. In two of them the nitrogenase activity was limited by addition of glucose. Aggregates of a larger diameter (2–4 mm) exhibited a considerably higher nitrogenase activity than those with a diameter smaller than 2 mm. This effect was even more pronounced when the soil samples were repeatedly intensively aerated. On the contrary, smaller aggregates (0.5–2 mm) exhibited more intensive nitrification.

Dinitrogen fixation — acetylene reduction in soybeans during the reproductive growth period

In a greenhouse pot oulture experiment, a dinitrogen (N2) fixing — acetylene reduction activity profile was examined in detail as affected by plant age. Total [μmol C2H4 root-1 h-1] and speoifio nitrogenase [nmol C2H4 (mg nodule d. wt.)-1 min-1] activities peaked 63 days after sowing, near the end of flowering. The nitrogenase activities, nodule dry matter accumulation, top dry matter accumulation, and total nitrogen yield in the top dry matter were found to be highly correlated.

Characterization of soil populations of Rhizobium leguminosarum bv. Viceae by means of symbiotic traits

Abstract Ten “whole-soil” populations of Rhizobium leguminosarum bv. viceae from different agricultural locations in Bohemia and Moravia were characterized phenotypically by using symbiotic or plant growth traits. The test plants, inoculated with diluted soil suspensions, were cultivated under standard growth conditions. Cluster analysis was used to segregate the populations into three groups. There were no clear-cut relationships between population groups and elevation of the locations or soil pH. When test plants were co-inoculated with soil suspensions and a standard inoculant strain, almost all segregated into the same group. This suggests that the inoculant strain was a very successful competitor under the experimental conditions used.

Gross carbon respiratory costs of symbiotic dinitrogen fixation in peas (Pisum sativum L.)

Summary Diurnal and seasonal fluctuations in nitrogenase C 2 H 2 -reducing activity, H 2 evolution and respiratory losses of CO 2 from nodules were studied in nodulated Pisum sativum L. as a basis for assessments of gross carbon and/or energy respiratory costs of symbiotic N 2 fixation. In 21 to 59-day-old pea plants the respiratory costs, expressed in the terms of carbon respirated per nitrogen fixed (GCC) and reflecting also the electron allocation for N 2 reduction and H 2 evolution, varied from 5.1 to 11.5 g C (g N) −1 . A seasonal average value was found to be 7.4 g C (g N) −1 .