Ludmila Lisá

The influence of exogenously supplied sucrose on glutamine synthetase and glutamate dehydrogenase levels in excisedPisum sativum roots

Glutamine synthetase (GS) level is positively influenced by exogenously supplied sucrose in isolated pea roots (similarly as nitrate reductase - NR), glutamate dehydrogenase (GDH) level negatively. Comparison with previous results shows that GS level decreases more slowly than NR level when sucrose is omitted from the medium; the rate of changes in GS level corresponds rather to that in GDH level. The increase in GDH level in the tips of isolated roots cultivated in the medium lacking sucrose stops after approx. 24 h, but continues for at least 72 h in more mature root parts. GS level decreases during the first 24 h in the tips of isolated roots (compared with roots of intact seedlings) cultivated both with sucrose and without it (without sucrose more), however it again rises in the course of further cultivation with sucrose. The differences in GS and GDH levels caused by omission of sucrose are small in isolated roots from which root tips were removed, the difference in NR level in decapitated roots is similar to that found in isolated roots with root tips left. Decapitated isolated roots cultivated without sucrose contain higher amounts of soluble sugars than corresponding roots with root tips left. These facts are dismissed with regard to sugar consumption, transport, and compartmentalisation, and with respect to production in root tips and other plant parts of unknown compounds involved in GS and GDH regulation. The results obtained suggest that GDH functions in pea roots in the deaminating direction.

The influence of sugars on nitrate reductase induction by exogenous nitrate or nitrite in excised pisum sativum roots

Nitrate reductase (NR) induction is enhanced by exogenously supplied sucrose in excised pea roots exposed to both exogenous nitrate and exogenous nitrite. NR synthesis is preferentially supported by sugars transported to the cells at the moment, however NR induction can take place for some time without exogenous sugar influx if roots are saturated with sugars during precultivation. Steady high NR levels are dependent on steady sugar and nitrate influxes. NR induction is low in roots precultivated for 20 h without sucrose although sugar content is still high in them. This suggests that compartmentation of sugars in the cells is of major importance during NR induction. Total nitrate content in roots exposed to nitrate is not influenced by sucrose supplied together with nitrate. Some nitrite is oxidized to nitrate in roots exposed to exogenous nitrite ; we assume that this nitrate is responsible for NR induction. Our results indicate that sugars, besides many indirect effects on NR induction, may also directly influence NR synthesis either as coinducers or as derepressors of NR synthesis. Our results further show that NR is not a product-inducible enzyme.

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.

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.

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.

Comparative response of Pisum sativum nodulated with indigenous soil Rhizobium populations and/or Co-inoculated with a Rhizobium leguminosarum strain. II : Nodulation, competition for nodulation, plant biomass and nitrogen accumulation

Plants nodulated byRhizobium populations from two soils that differed markedly in their acidity (Ruzyně soil pH=7.6, Lukavec soil pH=4.9) produced a significantly higher amount of the nodule dry mass per plant and a higher ratio of the nodule dry mass per unit of plant dry biomass in comparison with plants inoculated or co-inoculated (7×107 cells per seedling) with Hup+ strain 128C30. When inoculated with Lukavec soil, the nodulation was delayed. Production of dry plant biomass and the amount of nitrogen yielded by this biomass were by 10 and 16% (nodulated by Ruzyně soil population) and 30 and 34% (Lukavec soil population), respectively, lower than if inoculated or co-inoculated with 128C30. Potential dinitrogen fixation resulting from seasonal changes in acetylene-reducing and dihydrogen-evolving activities of the nodulated roots represented up to 40% of the total nitrogen of the plant biomass if nodulated with soil rhizobia and about 64% when inoculated or co-inoculated with 128C30. Co-inoculation with 128C30 together with the soil populations ofRhizobium resulted in an induction of more than 90% of the nodules by this strain.

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 .

The effect of cultivation temperature on nitrate reductase, glutamine synthetase and glutamate dehydrogenase levels in isolatedPisum sativum roots

Nitrate reductase (NR), glutamine synthetase (GS), and glutamate dehydrogenase (GDH) levels are differently influenced by cultivation temperature, NR level being influenced most and GDH level least. The differences caused by cultivation temperature are more pronounced in roots cultivated without sucrose in which a slower decrease in NR and GS levels and a lower increase in GDH level occur at 14 and 18 °C than at 24 °C in comparison to roots cultivated with sucrose. Sugar consumption also tends to be slower at 14 °C than at 24 °C in roots cultivated without sucrose.

Rhizobium leguminosarum strains forming nitrogen-rich nodules inPisum sativum

The nodules which developed on the roots ofPisum sativum after inoculation withRhizobium leguminosarum bv.viciae strains showing a Hup+ symbiotic phenotype and/or a high relative efficiency of electron transfer to dinitrogen (RE) had a high nitrogen content of their tissue. In comparison with the nodules initiated by a strain possessing the Hup− symbiotic phenotype or by an indigenous soilRhizobium population, the nitrogen-rich root nodules contained up to four times more nitrogen (9.2% of dry mass). In the nitrogen-rich nodules, total amino acid, and especially Ala, Lys and Phe contents were significantly increased. The nitrogen-rich nodule symbiotic phenotype (Nrn) was well expressed, irrespective of pea cultivars and host plant age. If a strain showing the Nrn phenotype was applied in double-strain inocula, a significant correlation was found between increasing rates of the strain and increasing percentage nitrogen content of nodule tissue in the nodulated plants.