Growth of Phaseolus vulgaris on Various Nitrogen Sources: The Importance of Urease

Rhizobium-inoculatcd plants of Phaseolus vulgaris L. were grownwith different N-sources (nitrate, ammonium, urea) and differentconcentrations of urea. The distribution of growth between plantparts varied with N-sources. Nitrate and ammonium were moreinhibitory to nodulation than urea, which at 40 mol m^–3N had no effect. Urease activity varied in amount and locationover a range of urea concentrations. At higher concentrations,more urea was transported to and increased urease activity wasfound in the shoot Lower levels of activity in plants relianton N₂-fixation were consistent with a ureide-degradation pathwaynot involving urea. Moderate doses of urea could be assimilatedconcomitantly with N₂-fixation. At higher levels of appliedurea, nodulation and ureide transport to the shoots were reduced,although increased growth could not be maintained at concentrationsof applied urea greater than 6.0 mol m^–3 urea N. Key words: Phaseolus vulgaris, growth, nitrogen source, urease     

The Effect of Various Nitrogen Sources upon Heterocyst Formation in Anabaena Flos-Aquae A-37

Heterocysts are formed abundantly in cultures of Anabaena flos-aquaeA-37 which are fixing nitrogen. Fewer are formed in the presenceof NO₃^– ions, whereas none occurred in the presence ofNH₄⁺ ions. The results indicate that heterocysts may have arole in nitrogen metabolism.     

Non-Frankia Actinomycetes Isolated from Surface-Sterilized Roots of Casuarina equisetifolia Fix Nitrogen

Based on partial 16S sequences, we previously described a novel group of nonsymbiotic, acetylene reduction activity-positive actinomycetes which were isolated from surface-sterilized roots of Casuarina equisetifolia growing in Mexico. An amplified rRNA restriction analysis confirmed that these actinomycetes are distinct from Frankia, a finding substantiated by a 16S rRNA gene phylogenetic analysis of two of the Mexican isolates. Further support for these actinomycetes being separate from Frankia comes from the very low DNA-DNA homology that was found. Nevertheless, the Mexican isolates may be diazotrophs based not only on their ability to grow in N-free medium and reduce acetylene to ethylene but also on the results from ¹⁵N isotope dilution analysis and the finding that a nifH gene was PCR amplified. A comparison of the nifH sequences from the various isolates showed that they are closely related to nifH from Frankia; the similarity was 84 to 98% depending on the host specificity group. An analysis of complete 16S rRNA gene sequences demonstrated that the two strains analyzed in detail are most closely related to actinobacteria in the Thermomonosporaceae and the Micromonosporaceae.     

The Growth and Physiology of Pinus strobus L. Seedlings as Affected by Various Nutritional Levels of Nitrogen and Phosphorus

Potted white pine (Pinus strobus L.) seedlings were grown ingravel either in outdoor cold frames or in growth chambers.They were watered every second day with a salt solution containingdifferent amounts of nitrogen and phosphorus. After 13 weeksof growth individual seedlings were illuminated separately for8 h in the presence of ¹⁴CO₂ and the rates of their apparentphotosynthesis, respiration, and translocation of recent ¹⁴C-photosynthateto their roots were observed. Roots were extracted with 80 percent ethanol and the nature of various ¹⁴C compounds in theextract was determined by paper chromatography. The best over-all growth of plants, mycorrhizal development,apparent photosynthesis, and translocation of recent photosynthateto the roots were observed in plants grown at the intermediatelevels of N and P nutrition. Sucrose was always the dominant form in which recently translocated¹⁴C occurred in the roots, although with increased nitrogensupply there was increased hydrolysis of sucrose to hexosesand appearance of ¹⁴C in the amino- and organic acids.     

The Effect of Combined Nitrogen on the Growth and Nodulation of Excised Roots of Phaseolus vulgaris L.

Isolated roots of Phaseolus vulgaris were grown in aseptic cultureusing a modified Raggio technique in which the organic nutrientsare fed to the cut (basal) end of the excised root while theroot tip grows into a mineral-salt solution inoculated withRhizobium. Treatments were applied to investigate the effectsof varying the level of sucrose in the organic medium and ofadding combined nitrogen as nitrate and urea to both media. There was a marked effect of sucrose on the growth and nodulationof the roots. Increasing the concentration increased the numberof nodules both per root and per unit fresh weight of tissue. The growth of the roots was not affected by the level of combinednitrogen. Nitrate in the mineral-salt solution markedly reducednodule numbers but in the agar medium it had only a slight delayingeffect on nodulation. Urea in either the mineral-salt solutionor the organic medium reduced nodule numbers though to a lesserextent than nitrate in the mineral-salt solution. The number of nodules formed was inversely correlated with thelevels of soluble and inorganic nitrogen compounds in the tissues. It is suggested that the adverse effect of combined nitrogenon nodulation is due to the accumulation of unsequestered nitrogencompounds and a depletion of carbohydrates generally withinthe root tissues rather than the local effect of any particularnitrogen compound.     

不同氮源对红花幼苗生长及营养成分影响

为了提高红花苗菜产量,探讨氮源与红花幼苗生长的关系,该研究以1-3、H-7和3-10红花株系为试验材料,采用盆栽砂培试验,以不施肥为对照,研究铵态氮、硝态氮、生物有机肥、尿素、生物有机肥/铵态氮、生物有机肥/硝态氮、生物有机肥/尿素、铵态氮/硝态氮等9个处理对红花幼苗生物学性状、可溶性糖、可溶性蛋白质、硝酸盐、羟基红花黄色素A、黄酮等的影响。结果显示:(1)与对照相比,所有施氮处理红花幼苗的株高、单株鲜质量、食用部分质量和生物学产量均有提高,其中尿素处理红花幼苗的食用部分质量、单株鲜质量和生物学产量最高,比对照平均增加了34.16%、25.15%和35.63%,产出比均值达81.94,其次为生物有机肥/硝态氮处理,比对照平均增加27.59%、21.78%和29.81%,产出比均值达78.18。(2)与对照相比,铵态氮和硝态氮处理均降低了红花幼苗可溶性糖含量,尿素处理显著增加红花幼苗可溶性蛋白含量,生物有机肥/尿素处理的幼苗可溶性蛋白含量仅低于尿素处理。(3)铵态氮、硝态氮和尿素与生物有机肥配施处理,红花幼苗的硝酸盐含量增加幅度小于铵态氮、硝态氮和尿素单施,表明生物有机肥处理可降低红花幼苗的硝酸盐含量。(4)不同氮源对红花幼苗羟基红花黄色素A没有显著影响;与对照相比,仅生物有机肥/硝态氮处理的红花幼苗中黄酮略有增加,其他处理的黄酮含量均下降。研究表明,氮源为生物有机肥/硝态氮时,红花幼苗生物学产量、可溶性糖、可溶性蛋白和黄酮含量相对较高,而硝酸盐含量相对较低,为红花苗菜生产最佳氮源。     

Effect of Various Light Treatments on Chlorophyll Formation in Excised Potato Roots

Potato root tips were grown in cultures and the effect of blue, red, and white light on chlorophyll formation was studied. The roots grown in white light turned green in 4–6 weeks, whereas in blue or red light, green colour occasionally appeared at places. The chlorophyll contents, as determined by the spectrophotometeric method, were found to be maximum in unfiltered light followed by blue and red light. In white and blue light treatments chlorophyll a contents were higher than chlorophyll b, however in red light this was reversed. The results are compared with earlier experiments on chlorophyll formation in excised roots.     

Diversification of Nitrogen Sources in Various Tundra Vegetation Types in the High Arctic

Low nitrogen availability in the high Arctic represents a major constraint for plant growth, which limits the tundra capacity for carbon retention and determines tundra vegetation types. The limited terrestrial nitrogen (N) pool in the tundra is augmented significantly by nesting seabirds, such as the planktivorous Little Auk (Alle alle). Therefore, N delivered by these birds may significantly influence the N cycling in the tundra locally and the carbon budget more globally. Moreover, should these birds experience substantial negative environmental pressure associated with climate change, this will adversely influence the tundra N-budget. Hence, assessment of bird-originated N-input to the tundra is important for understanding biological cycles in polar regions. This study analyzed the stable nitrogen composition of the three main N-sources in the High Arctic and in numerous plants that access different N-pools in ten tundra vegetation types in an experimental catchment in Hornsund (Svalbard). The percentage of the total tundra N-pool provided by birds, ranged from 0–21% in Patterned-ground tundra to 100% in Ornithocoprophilous tundra. The total N-pool utilized by tundra plants in the studied catchment was built in 36% by birds, 38% by atmospheric deposition, and 26% by atmospheric N₂-fixation. The stable nitrogen isotope mixing mass balance, in contrast to direct methods that measure actual deposition, indicates the ratio between the actual N-loads acquired by plants from different N-sources. Our results enhance our understanding of the importance of different N-sources in the Arctic tundra and the used methodological approach can be applied elsewhere.     

不同氮源对球形棕囊藻生长的影响

采用实验室培养的方法比较了6种不同氮源-硝态氮、尿素、甘氨酸、精氨酸、谷氨酸、腺嘌呤对典型赤潮藻球形棕囊藻(Phaeocystis globosa)生长的影响。结果表明,6种氮源均能不同程度地促进球形棕囊藻的生长,但比生长速率和光合作用效率具有显著差异性。将球形棕囊藻在不同浓度氮源下的最大比生长速率分别拟合Monod方程,得出球形棕囊藻在硝态氮、尿素、甘氨酸、精氨酸、谷氨酸和腺嘌呤等6种氮源下的最大比生长率分别为1.05,1.17,0.82,0.87,1.09,0.90d^-1,相应的半饱和常数分别为9.132,23.758,85.519,7.104,23.94,10.959μmol/L。其中,高氮浓度(8820μmol/L)下腺嘌呤对球型棕囊藻的生长具有显著抑制作用。相比较而言,球形棕囊藻对甘氨酸的亲和力最高。当硝态氮、尿素、甘氨酸、精氨酸、谷氨酸和腺嘌呤的浓度分别为8820,882,882,8820,882,0.441μmol/L时,球形棕囊藻的最大光合效率(Fv/Fm)分别为0.619,0.620,0.579,0.595,0.648,0.667。由此可见,氮源对球形棕囊藻的生长和光合作用具有显著影响;球形棕囊藻能够利用多种无机和有机氮源,与其它仅能利用无机氮源的浮游植物相比,更具有竞争优势。     

The Effect of Several Protein Amino Acids and Some Inorganic Nitrogen Sources on the Growth of Sphagnum nemoreum

The nitrogen metabolism of a bog moss, Sphagnum nemoreum Scop., has been studied in aseptic cultures. The effect of several protein amino acids, especially those found in peat, has been investigated. NH₄NO₃ (1.25 mM) was the best nitrogen source but NH₄⁺ ions were more effectively utilized than NO₃⁻ ions when given as the only nitrogen source. Some of the amino acids (2.5 mM) allowed fairly satisfactory growth (arginine and alanine) when given as the only nitrogen source, but some of them were not utilized at all (leucine, lysine, isoleucine and methionine). Given at low concentrations (0.001 and 0.25 mM) together with NH₄NO₃ (2.5 mM), most of the protein amino acids failed to reveal any growth-promoting or -inhibiting effect. Only lysine (0.25 mM) clearly inhibited growth under these conditions. The nitrogen metabolism of Sphagnum nemoreum seems to be rather flexible and this species is more tolerant of organic nitrogen, especially hydroxyproline, than the higher plants.     

碳源和氮源对黑盖木层孔菌菌丝生长的影响

研究了四种碳源(蔗糖、乳糖、葡萄糖、可溶性淀粉)和九种氮源(玉米面、麸皮、马铃薯、大豆粉、酵母粉、蛋白胨、硝酸钾、硝酸铵、尿素)对黑盖木层孔菌菌丝生长的影响。从不同代数的菌丝体中提取多糖,并测定多糖含量、分子量分布范围及单糖组成。结果表明:黑盖木层孔菌菌丝生长的最佳碳源为可溶性淀粉,最佳氮源为玉米面,最优碳氮组合为蔗糖和玉米面的组合。不同代数的菌丝体多糖性状基本稳定。     

Growth and Transcriptional Changes in Poplar Under Different Nitrogen Sources

Plant Molecular Biology Reporter - Nitrogen greatly affects primary plant growth and development. The relationship between nitrogen availability and source and its effect on secondary growth is...