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21.
Summary Remobilization of15N from vegetative tissue of mungbean (Vigna radiata (L.) Wilczek) into pods was measured during the reproductive phase of growth. Plant tissue was labelled with15N during vegetative development. Experiments were conducted in the field at two sites. At one site the soil provided cowpeas
with most of their N but at the other site N fixation provided most of the N. Remobilized N from vegetative tissue to pods
occurred soon after they began to develop. The quantity of the labelled N ultimately remobilized to the pods amounted to 50%
for one cultivar (Tx33) at the high soil N site and 70% at the low N site. For the other cultivar (Tx13) the values were 25%
and 30%, respectively. The two cultivars performed very differently with respect to partitioning of N into pods and the rate
of N fixation. Even though more N was accumulated in the shoots of the high N fixing cultivar (Tx13) less total N was contained
in the pods. 相似文献
22.
Effects of photoperiodicity and light irradiance on phosphate-limited Oscillatoria agardhii in chemostat cultures 总被引:1,自引:0,他引:1
Oscillatoria sp. strain 23 is a filamentous, non-heterocystous cyanobacterium that fixes nitrogen aerobically. Although, in this organism nitrogenase is inactivated by oxygen a high tolerance is observed. Up to a pO2 of 0.15 atm, oxygen does not have any measurable effects on acetylene reduction. Higher concentrations of oxygen inhibited the activity to a relatively high degree. Evidence for two mechanisms of oxygen protection of nitrogenase in this cyanobacterium was obtained. A high rate of synthesis of nitrogenase may allow the organism to maintain a certain amount of active enzyme under aerobic conditions. Secondly, a switch off/on mechanism may reversibly convert the active enzyme into a non-active form which is insensitive to oxygen inactivation after a sudden and short-term exposure to high oxygen concentrations. It is conceived that these mechanisms in addition to a temporal separation of nitrogen fixation from oxygenic photosynthesis sufficiently explain the regulation process of aerobic nitrogen fixation in this organism.Abbreviations DCMU
3-(3,4-dichlorophenyl)-1,1-dimethylurea
- CAP
chloramphenicol 相似文献
23.
The potential nitrogen sources for the primary production in the intertidal area are nitrogen compounds obtained from mineralization in the sediment and the water column, nitrogen fixation, outflow from rivers and groundwater seeping from the mainland. The available inorganic nitrogen in the adjacent coastal waters decreases from 50–80 μmol NO3 -/l and 6–15 μmol NH4 +/l in early spring to ca one tenth during the growing season. In the sediment of the tidal flats available ammonia and nitrate vary between 50 and 100 μmol/1 pw. In the salt marsh available ammonia increases from 200–300 nmol NH4 +/g fwt to approximately double the amount, and the available nitrate varies from 100–300 nmol NO3 -/g fwt (250–750 μmol NO3 -/l pw) to ca one third during the growing season. The exchange of NH4 +, NO2 - and NO3 - across the sediment water interface has been estimated during tidal cycles under light and dark conditions on the tidal flats. The flux of nitrogen was dependent on the flora and fauna as well as the time of the year. The tidal activity, frequency and length of inundation are considered the driving force in a two-way process between salt marshes and adjacent coastal waters. The role of marsh sediment, tidal water and sediments of the tidal flats as sites of accumulation, consumption and remineralization of organic matter is emphasized. The possible exchange of ammonia and nitrate between the salt marsh and the different compartments of the tidal water is discussed. 相似文献
24.
The phylogenetically related phototrophic bacteria Rhodospirillum tenue and Rhodocyclus purpureus modulate activity of their glutamine synthetases by adenylylation/deadenylylation. Evidence for covalent modification includes the inhibitory effect of Mg2+ on the activity of glutamine synthetase extracted from cells of either species grown on excess ammonia, and the lack of Mg2+ inhibition of activity of the enzyme isolated from N2-(R. tenue) or glutamine (R. purpureus)-grown cells. In addition, snake venom phosphodiesterase treatment of glutamine synthetase from either species grown on excess ammonia relieved Mg2+ inhibition of the enzyme (as measured via the -glutamyl transferase assay), and changed the cation specificity from Mn2+ to Mg2+ (in the biosynthetic assay). 相似文献
25.
Dry matter and nitrogen accumulation and partitioning in selected soybean genotypes of different derivation 总被引:2,自引:0,他引:2
P. B. Cregan R. W. Yaklich 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1986,72(6):782-786
Summary Experiments were conducted to determine if changes in the accumulation and partitioning of dry matter (DM) and nitrogen (N) in soybean [Glycine max (L.) Merr.] were associated with agronomic improvements and to assess the degree of genetic variation present for these traits. Fifteen maturity group II soybean genotypes including three ancestral cultivars, three modern cultivars, and nine agronomically superior plant introductions (PI's) were grown in replicated tests at four locations in the eastern U.S. The DM and N of stems, pod walls, and seeds were determined at maturity, and the apparent harvest indices (HI) and the apparent nitrogen harvest indices (NHI) were calculated. Pod DM partitioning was calculated as the ratio of seed DM to total pod DM and pod N partitioning was the ratio of seed N to total pod N. The mean DM accumulation of the modern cultivars was significantly greater than that of the ancestral cultivars and PI's. The apparent HI and the pod DM partitioning of both the modern and ancestral cultivars were significantly higher than that of the PI's. The three modern cultivars demonstrated the highest N accumulation. As a group, the modern cultivars consistently showed maximal accumulation and partitioning of DM and N suggesting that these physiological traits are associated with agronomic improvement. No individual PI was found to possess DM or N accumulation or partitioning which significantly exceeded the best modern cultivar or ancestral cultivar, indicating that genotypes with accumulation or partitioning characteristics which exceed available germplasm may be difficult to identify. Seed yield was correlated (P<0.05) with both DM (r=0.61) and N (r=0.57) accumulation. 相似文献
26.
G. Schilling 《Plant and Soil》1983,72(2-3):321-334
Summary Mineral nitrogen did not increase grain yield and seed protein levels ofVicia faba L. andLupinus luteus L. in field trials and pot experiments. Fixed N2 was substituted by mineral nitrogen in these cases because of inhibition of N2 fixation by mineral nitrogen. Contrary to these results mineral nitrogen increased grain yields and seed protein amounts ofLupinus albus L.,Pisum sativum L., andGlycine max. (L.) Merr. The nitrogen effect was caused at an early stage by saving energy due to inhibition of N2 fixation (measurement of gas exchange by means of IRGA). In case of the N application after flowering grain, yields and seed protein levels increased because the mineral N was an additional nitrogen source for plants. At this stage the plants had ceased fixing atmospheric nitrogen. The high sink activity of growing fruits induced a lack of assimilates in nodules (determined by means of14CO2 application). The N effect was therefore the consequence of the lower assimilate pool for supplying root nodules in these plants in comparison withVicia faba L. andLupinus luteus L. Hence it follows that response to mineral nitrogen can be a criterion for discovering more effective Rhizobium-host combinations. 相似文献
27.
Trypanosoma congolense. I. Clinical observations of experimentally infected cattle 总被引:12,自引:0,他引:12
B. Wellde R. Lötzsch G. Deindl E. Sadun J. Williams G. Warui 《Experimental parasitology》1974,36(1):6-19
The course of disease was studied in 8 cattle infected with Trypanosoma congolense. Although the onset of patency was dependent on the numbers of infecting organisms, the duration of the infection was not. High fevers were present on the day of or the day after initial patency. Succeeding peaks of parasitemia, and a progressive weight loss of over 30% occurred. A decrease in packed cell volume (PCV) beginning the first week after infection was observed. Early in the course of the developing anemia, many polychromatophilic erythrocytes and occasional normoblasts were found in the blood. A leucopenia persisted for the duration of the disease. Total serum protein concentrations fell sharply during the first 5 weeks of infection, then gradually increased to low normal levels. Serum albumin levels followed a similar pattern for the first 5 weeks, and remained at a relatively low level. Although gamma globulin levels also declined during the first 5 weeks, their levels gradually surpassed those of preinfection samples. No marked changes in serum glucose were noted. A mild elevation of serum urea nitrogen values occurred early during infection, but subsided. The animals dying early after infection developed elevated total bilirubin levels. 相似文献
28.
29.
Pamela Matson 《Oecologia》1990,85(2):241-246
Summary Plant nutrient status and physiological processes were examined in relation to soil nutrient characteristics under individuals of five species colonizing a young cinder deposit in Hawaii Volcanoes National Park. Two exotic species, Buddeleja asiatica and Myrica faya, had high photosynthetic rates and high nitrogen concentrations and relatively easily decomposed leaves; soils under them had high concentrations of nitrogen, cations, and organic matter and high rates of net nitrogen mineralization. At the other extreme, the natives Metrosideros polymorpha and Vaccinium reticulatum had low plant concentrations and photosynthetic rates, and low concentrations and turnover rates of N in the soil. Thus, a strong correlation exists between soil processes and plant processes, suggesting a positive feedback cycle. 相似文献
30.
Peter Högberg 《Oecologia》1990,84(2):229-231
Summary Urea (U) and ammonium nitrate (AN) had been applied to a Scots pine (Pinus sylvestris L.) forest in northern Sweden for 18 consecutive years at four doses resulting in total N applications ranging from 0 to 1980 kg ha–1. The 15N abundance ( 15N) of the grass Deschampsia flexuosa (L.) Trin. increased linearly (from –0.7 to 11.0) with application rate in the case of U. The response to AN was in the same direction but smaller. While others have shown that the initial response of nitrogen-limited systems to additions of N is a change of 15N abundance towards that of added N, this study shows that further and excessive additions leads to a retention of 15N. Monitoring 15N abundance over time in dose-response trials of this type thus opens new possibilities to estimate critical loads of N and the point of nitrogen saturation. 相似文献