Phylogeny of Nannizzia incurvata,N. gypsea,N. fulva and N. otae by restriction enzyme analysis of mitochondrial DNA

Sequence divergence among Nannizzia incurvata, N. gypsea, N. fulva and N. otae was studied genetically using digestion profiles of mitochondrial DNA with restriction enzymes, Hae III, Hha I, Hind III and Xba I. Only N. fulva was subdivided into two types on restriction profiles. Phylogenetic relationships suggest that 1) N. gypsea is more closely related to N. fulva than N. incurvata, 2) the phylogenetic distance between N. otae and the other three species is larger than the distances between the other three species.     

Effects of Dry-Season N Input on the Productivity and N Storage of Mediterranean-Type Shrublands

Anthropogenic nitrogen (N) deposition is a globally important source of N that is expected to increase with population growth. In southern California, N input from dry deposition accumulates on vegetation and soil surfaces of chaparral and coastal sage scrub (CSS) ecosystems during the summer and fall and becomes available as a pulse following winter rainfall. Presumably, N input will act to stimulate the productivity and N storage of these Mediterranean-type, semi-arid shrublands because these ecosystems are thought to be N limited. To assess whether dry-season N inputs alter ecosystem productivity and N storage, a field experiment was conducted over a 4-year period where plots were exposed to either ambient N deposition (control) or ambient + 50 kgN ha⁻¹ y⁻¹ (added N) that was added as NH₄NO₃ during the fall dry-season of each year. Plots exposed to added N had significantly higher accumulation of NH₄ and NO₃ on ion exchange resins that was due in part to direct fertilization and N mineralization, and the increase in N availability lead to a significant increase in NO₃ leaching in chaparral but not CSS. Nitrogen addition also lead to an increase in litter and tissue N concentration and a decline in the C:N ratio, but failed to alter the ecosystem productivity and N storage of the chaparral and CSS shrublands over the 4-year study period. The reasons for the lack of a treatment response are unknown; however, it is possible that these semi-arid shrublands are not N limited, cannot respond rapidly enough to capture the ephemeral N pulse, are limited by other nutrients, or the N response is dependent on the amount and/or distribution of rainfall. These results have important implications for understanding the potential effects of anthropogenic N deposition on the C and N cycling and storage of Mediterranean-type, semi-arid shrublands. Author Contributions  GLV conceived or designed study, performed research, analyzed data, contributed new methods or models, and wrote the article. SCP performed research, analyzed data, and contributed to the writing of the article. RM performed research, analyzed data, and contributed to the writing of the article.     

Natural 15N abundance of soil N pools and N2O reflect the nitrogen dynamics of forest soils

Natural ¹⁵N abundance measurements of ecosystem nitrogen (N) pools and ¹⁵N pool dilution assays of gross N transformation rates were applied to investigate the potential of δ¹⁵N signatures of soil N pools to reflect the dynamics in the forest soil N cycle. Intact soil cores were collected from pure spruce (Picea abies (L.) Karst.) and mixed spruce-beech (Fagus sylvatica L.) stands on stagnic gleysol in Austria. Soil δ¹⁵N values of both forest sites increased with depth to 50 cm, but then decreased below this zone. δ¹⁵N values of microbial biomass (mixed stand: 4.7 ± 0.8‰, spruce stand: 5.9 ± 0.9‰) and of dissolved organic N (DON; mixed stand: 5.3 ± 1.7‰, spruce stand: 2.6 ± 3.3‰) were not significantly different; these pools were most enriched in ¹⁵N of all soil N pools. Denitrification represented the main N₂O-producing process in the mixed forest stand as we detected a significant ¹⁵N enrichment of its substrate NO₃⁻ (3.6 ± 4.5‰) compared to NH₄⁺ (−4.6 ± 2.6‰) and its product N₂O (−11.8 ± 3.2‰). In a ¹⁵N-labelling experiment in the spruce stand, nitrification contributed more to N₂O production than denitrification. Moreover, in natural abundance measurements the NH₄⁺ pool was slightly ¹⁵N-enriched (−0.4 ± 2.0 ‰) compared to NO₃⁻ (−3.0 ± 0.6 ‰) and N₂O (−2.1 ± 1.1 ‰) in the spruce stand, indicating nitrification and denitrification operated in parallel to produce N₂O. The more positive δ¹⁵N values of N₂O in the spruce stand than in the mixed stand point to extensive microbial N₂O reduction in the spruce stand. Combining natural ¹⁵N abundance and ¹⁵N tracer experiments provided a more complete picture of soil N dynamics than possible with either measurement done separately.     

Plant and Soil N Response of Southern Californian Semi-arid Shrublands After 1 Year of Experimental N Deposition

Large inputs of atmospheric N from dry deposition accumulate on vegetation and soil surfaces of southern Californian chaparral and coastal sage scrub (CSS) ecosystems during the late-summer and early-fall and become available as a pulse following winter rainfall; however, the fate of this dry season atmospheric N addition is unknown. To assess the potential for dry season atmospheric N inputs to be incorporated into soil and/or vegetation N pools, an in situ N addition experiment was initiated in a post-fire chaparral and a mature CSS stand where 10 × 10 m plots were exposed to either ambient N deposition (control) or ambient +50 kg N ha⁻¹ (added N) added as NH₄NO₃ during a single application in October 2003. After 1 year of N addition, plots exposed to added N had significantly higher accumulation of extractable inorganic N (NH₄−N + NO₃−N) on ion exchange resins deployed in the 0–10 cm mineral soil layer and higher soil extractable N in the subsurface (30–40 cm) mineral soil than plots exposed to ambient N. Chaparral and CSS shrubs exposed to added N also exhibited a significant increase in tissue N concentration and a decline in the tissue C:N ratio, and added N significantly altered the shrub tissue δ ¹⁵N natural abundance. Leaching of inorganic N to 1 m below the soil surface was on average 2–3 times higher in the added N plots, but large within treatment variability cause these differences to be statistically insignificant. Although a large fraction of the added N could not be accounted for in the shrub and soil N pools investigated, these observations suggest that dry season N inputs can significantly and rapidly alter N availability and shrub tissue chemistry in Mediterranean-type chaparral and CSS shrublands of southern California.     

Enzyme immunoassays of N 6-benzyladenine and N 6-(meta-hydroxybenzyl)adenine cytokinins

Enzyme-linked immunosorbent assays (ELISAs) were developed for determination of N ⁶-benzyladenosine, N ⁶-(meta-hydroxybenzyl)adenosine, and structurally related cytokinins. The use of the ELISAs allowed detection over the range of 0.05–70 pmol for N ⁶-benzyladenine and 0.01–20 pmol for the N ⁶-(meta-hydroxybenzyl)adenine cytokinins. Polyclonal antibodies used in the assays were specific for N ⁶-benzyladenine and N ⁶-(meta-hydroxybenzyl)adenine and their corresponding N ⁹-substituted derivatives. By the use of internal standardization, dilution assays, authentic [2-³H]cytokinin recovery markers, and immunohistograms, the ELISAs have been shown to be applicable for the estimation of N ⁶-benzyladenine and N ⁶-(meta-hydroxybenzyl)adenine-type cytokinins in plant tissues. For the analysis of cytokinins in the tissues of young poplar leaves and Solarium teratoma shoot culture, the extracts were fractionated by high performance liquid chromatography (HPLC) and the fractions analyzed by ELISAs. Immunohistogram ELISA analysis of fractions from different HPLC systems indicated major peaks of immunoreactivity co-chromatographing with the labeled and unlabeled standards of N ⁶-benzyladenine, N ⁶-meta-hydroxybenzyl)adenine, and their N ⁹-glycosides in these tissues.Abbreviations ELISA enzyme-linked immunosorbent assay - FW fresh weight - (mOH)[9R]BAP N ⁶-(meta-hydroxybenzyl)adenosine - HPLC high performance liquid chromatography - TBS Tris-buffered saline - TEAA triethylammonium acetate - [9R]BAP N ⁶-benzyladenosine     

Dynamics of biomass and N accumulation of alfalfa under three N fertilization rates

The dynamics of biomass and N accumulation following defoliation of alfalfa and the application of N fertilization has rarely been studied under field conditions, particularly in the seeding year. Our objectives were to determine the effect of N fertilization on the dynamics of biomass and N accumulation during the first regrowth of alfalfa in the seeding year, and to determine if a model describing critical N concentration developed for established stands could be used in the seeding year. In two separate experiments conducted in 1992 and 1993, the biomass and N accumulation of alfalfa grown with three N rates (0, 40 and 80 kg N ha^-1) were determined weekly. Maximum shoot growth was reached with 40 kg N ha^-1 in 1992, and maximum shoot growth was not reached with the highest N fertilization rate in 1993. Nitrogen fixation, root N reserves and soil inorganic N uptake when no N was applied were, therefore, not sufficient to ensure non-limiting N conditions, particularly when growth rates were the highest between 14 to 21 d after defoliation. Nitrogen fertilization increased shoot biomass accumulation in the first 21 d of regrowth, biomass partitioning to the shoots and shoot and taproot N concentrations. The model parameters of critical N concentration developed by Lemaire et al. (1985) for established stands of alfalfa were not adequate in the seeding year. The N requirements per unit of shoot biomass produced are greater in the seeding year than on established stands, and this was attributed to a greater proportion of leaves in the seeding year.     

N G,N G -Dimethyl-l-arginine,a dominant precursor of endogenous dimethylamine in rats

Summary The metabolic significance ofN ^G ,N ^G -dimethyl-l-arginine (DMA) as a precursor of endogenous dimethylamine (DMN) in rats was examined in connection with the wide distribution and active operation of dimethylargininase (EC3.5.3.18) in rat tissues (Kimoto et al., 1993). When [methyl-¹⁴C]DMA was administered intraperitoneally to rats, the radioactive DMN was detected in various tissues as a major radioactive metabolite one hour after injection, and about 65% of the radioactivity administered was recovered in the first 12-h urine as DMN. In the case of the [¹⁴C] DMN-injected rats, almost all the radioactivity was excreted in the 12-h urine as DMN, except for a negligible amount of radioactivity found in urea. The time-dependent decrease in the specific radioactivity of DMA and DMN in urine showed that dimethylargininase was significantly involved in thein vivo formation of DMN by the hydrolytic cleavage of DMA released from methylated proteins and that DMA is a dominant precursor of endogenous DMN in rats.     

N deposition, N transformation and N leaching in acid forest soils

Nitrogen deposition, mineralisation, uptake and leaching were measured on a monthly basis in the field during 2 years in six forested stands on acidic soils under mountainous climate. Studies were conducted in three Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco] plantations (D20: 20 year; D40: 40 yr; D60: 60 yr) on abandoned croplands in the Beaujolais Mounts; and two spruce (Picea abies Karst.) plantations (S45: 45 yr; S90: 90 yr) and an old beech (Fagus sylvatica L.) stand (B150: 150 yr) on ancient forest soils in a small catchment in the Vosges Mountains. N deposition in throughfall varied between 7–8 kg ha^–1 year^–1 (D20, B150, S45) and 15–21 kg ha^–1 yr^–1 (S90, D40, D60). N in annual litterfall varied between 20–29 kg ha^–1 (D40, D60, S90), and 36–43 kg ha^–1 (D20, S45, B150). N leaching below root depth varied among stands within a much larger range, between 1–9 kg ha^–1 yr^–1 (B150, S45, D60) and 28–66 kg ha^–1 yr^–1 (D40, S90, D20), with no simple relationship with N deposition, or N deposition minus N storage in stand biomass. N mineralisation was between 57–121 kg ha^–1 yr^–1 (S45, D40, S90) and between 176–209 kg ha^–1 yr^–1 in (B150, D60 and D20). The amounts of nitrogen annually mineralised and nitrified were positively related. Neither general soil parameters, such as pH, soil type, base saturation and C:N ratio, nor deposition in throughfall or litterfall were simply related to the intensity of mineralisation and/or nitrification. When root uptake was not allowed, nitrate leaching increased by 11 kg ha^–1 yr^–1 at S45, 36 kg ha^–1 yr^–1 at S90 and between 69 and 91 kg ha^–1 yr^–1 at D20, D40, B150 and D60, in relation to the nitrification rates of each plot. From this data set and recent data from the literature, we suggest that: high nitrification and nitrate leaching in Douglas-fir soils was likely related to the former agricultural land use. High nitrification rate but very low nitrate leaching in the old beech soil was related to intense recycling of mineralised N by beech roots. Medium nitrification and nitrate leaching in the old spruce stand was related to the average level of N deposition and to the deposition and declining health of the stand. Very low nitrification and N leaching in the young spruce stand were considered representative of fast growing spruce plantations receiving low N deposition on acidic soils of ancient coniferous forests. Consequently, we suggest that past land use and fine root cycling (which is dependent on to tree species and health) should be taken into account to explain the variability in the relation between N deposition and leaching in forests.     

Progress on the genetics of the N2-fixing actinorhizal symbiont Frankia

The actinomycete Frankia is of fundamental and ecological interests for several reasons including its wide distribution, its ability to fix nitrogen, differentiate into sporangium and vesicle (specialized cell for nitrogen-fixation), and to nodulate plants from about 24 genera. Here, we present a review on the genetics performed so far on Frankia. At the end of July 2001, 293 kbp of Frankia DNA sequences were found in the databases. Thirty five percent of these sequences corresponded to full gene or gene cluster sequences. These genes could be divided according to their role into 6 key activities: gene translation (rrnA and tRNA ^pro gene), proteolysis (pcr genes), assimilation of ammonium (glnA and glnII), protection against superoxide ions (sodF), nitrogen fixation (nif cluster), and plasmid replication. We present a review of these genetic islands; their function, expression, localization and particular properties are discussed. A comparative analysis of Frankia nif genes from various strains and species is presented. An improved nomenclature for some of these genes is suggested to avoid conflicts. Frankia plasmids DNA sequences are also presented. The novel trends in Frankia genetics are described.     

The influence of shading on associative N2 fixation

Summary The effect of reduced solar radiation on associative N₂-fixation and plant parameters was studied in three field experiments (1978–80). Gahi-3 pearl millet (Pennisetum americanum (L.) K. Monch.) field plots were shaded with saran shade cloth that reduced solar radiation by 50% and 75%. Acetylene reduction activity (ARA) was reduced by shading in one of the three experiments. The two non-responding experiments were conducted on a wall-drained, low-activity site (ARA means ranging 17–68 n moles ethylene core^–1 h^–1), the responding experiment was conducted on a poorly drained, high-ARA site.Shading affected the plants drastically, reducing fresh weight and dry matter yields up to 46% (50% shade) and 57% (75% shade). Shading also reduced dry matter percentage from 19.6 (no shade) to 15.3 (75% shade) and increased nitrogen content from 0.6% (no shade) to 1.53% (75% shading). However, shading did not affect protein yield. Inoculation withAzospirillum brasilense had no measurable effect on yield or acetylene reduction in the first two experiments.In the third experiment, shading reduced mean ARA of inoculated plots over 100% but had no significant effect on control plots. Inoculation significantly increased ARA in the nonshaded plots but not in shaded plots. Acetylene reduction activity was high, with means ranging between 208 and 465 n moles ethylene evolved core^–1 h^–1. Soil moisture and millet growth stage also affected acetylene reduction activity.     

Influence of urea on biological N2 fixation and N transfer from Azolla intercropped with rice

The N₂ fixed by Azolla before and after urea application during the rice cycle, the mineralisation of Azolla-N as well as its availability to rice was studied in two greenhouse experiments conducted in 1996 and 1997 and in June 1998 in Goettingen (Germany). Dry matter production of the various rice parts of experiment 1 showed a clear positive synergism between treatment with Azolla and urea with a resulting apparent N recovery by rice increasing from 40% (without Azolla) to 57% in the presence of Azolla. Part of this increase may be due to N fixed biologically by Azolla and transferred to the rice. The second experiment shed some light on the role of BNF. Using an iterative method of estimation, the daily rate of N fixation was estimated at 0.6 – 0.7 kg N ha^–1. The rate was not so much affected by the age of the Azolla crop. At this rate, the BNF would amount to up to 100 kg N ha^–1 over a 130-day season. Assuming that BNF may be inhibited for a period of 5 – 10 days following urea application due to high levels of N in the floodwater, this might reduce the BNF by between 6 and 14 kg N ha over the season. Using the mean-pool-abundance concept, it was estimated that around 75 – 80% of the Azolla-N mineralized during the growth period was actually absorbed by the rice plants. Of the N taken up by rice around 28% was derived from the biologically fixed Azolla N, the remainder was urea N cycled through the Azolla. Azolla also seems to help sustain the soil N supply by returning N to the soil in quantities roughly equal to those extracted from the soil by the rice plant.     

Cloning and morphological properties of Nicgl;CYCD3;1 gene in genetic tumors from interspecific hybrid of N. langsdorffii and N. glauca

Plant genetic tumors represent neoplastic growths, which arise spontaneously in hybrid plants without apparent external induction. To understand the molecular nature of unregulated cell proliferation, a cyclin D cDNA clone encoding a cyclin D of 1104bp was isolated from a genetic tumor and designated Nicgl;CYCD3;1 gene. DNA gel blot analysis suggested that there are two copies of Nicgl;CYCD3;1 in the genetic tumors. Northern analysis showed that this gene had the highest expression level in genetic tumor compared to Nicotiana glauca, N. langsdorffii and hybrid plants. Plant morphology of hybrid plant was an intermediate between N. glauca and N. langsdorffii and was altered in the genetic tumors. The cell cycle distribution in N. glauca was G0/G1, 90.59; S, 0.60; G2/M, 8.81; in N. langsdorffii it was G 0/G1, 86.22; S, 6.90; G2/M, 6.88; in hybrid plants it was G 0/G1, 96.40; S, 1.79; G2/M, 1.81; and in genetic tumors G 0/G1, 74.70; S, 2.35; G2/M, 22.94. These data provide new insights into the molecular mechanisms underlying genetic tumor formation from interspecific hybrid between N. langsdorffii and N. glauca.     

Inoculation of forage grasses with N2-fixing Enterobacteriaceae

Summary Previous investigations indicated some forage grass roots in Texas are heavily colonized with N₂-fixing bacteria. The most numerous N₂-fixing bacteria were in the genera Klebsiella and Enterobacter. In the present investigation inoculation experiments were conducted using 18 isolates of these bacteria to determine if a N₂-fixing association could be established between the bacteria and the grassesCynodon dactylon andPanicum coloratum. Plants were grown in soil for approximately 5 months in a greenhouse and were measured periodically for dry matter, nitrogen accumulation, and acetylene reduction activity. Results of the investigation indicated that 25% of the plant-soil systems were active in acetylene reduction and the activity was high enough to indicate agronomically significant quantities of N₂ were being fixed (>8kg N ha⁻¹). However, plant systems extrapolated to fix>8 kg N ha⁻¹ contained less nitrogen and accumulated less dry matter than plants less active in acetylene reduction. Inocula could not be re-isolated from healthy grass roots indicating that the N₂-fixing activity may have not have been closely assiciated with plant roots. Future research is needed to determine factors limiting colonization of grass roots.     

Fixation of [13N]N2 and transfer of fixed nitrogen in the Anthoceros-Nostoc symbiotic association

The initial product of fixation of [¹³N]N₂ by pure cultures of the reconstituted symbiotic association between Anthoceros punctatus L. and Nostoc sp. strain ac 7801 was ammonium; it accounted for 75% of the total radioactivity recovered in methanolic extracts after 0.5 min and 14% after 10 min of incubation. Glutamine and glutamate were the primary organic products synthesized from [¹³N]N₂ after incubation times of 0.5–10 min. The kinetics of labeling of these two amino acids were characteristic of a precursor (glutamine) and product (glutamate) relationship. Results of inhibition experiments with methionine sulfoximine (MSX) and diazo-oxonorleucine were also consistent with the assimilation of N₂-derived NH ₄ ⁺ by Anthoceros-Nostoc through the sequential activities of glutamine synthetase (EC 6.3.1.2) and glutamate synthase (EC 1.4.7.1), with little or no assimilation by glutamate dehydrogenase (EC 1.3.1.3). Isolated symbiotic Nostoc assimilated exogenous ¹³NH ₄ ⁺ into glutamine and glutamate and their formation was inhibited by MSX, indicating operation of the glutamine synthetase-glutamate synthase (GS-GOGAT) pathway: However, relative to free-living cultures, isolated symbiotic Nostoc assimilated 80% less exogenous ammonium into glutamine and glutamate, implying that symbiotic Nostoc could assimilate only a fraction of N₂-derived NH ₄ ⁺ . This implication was tested by using Anthoceros associations reconstituted with wild-type or MSX-resistant strains of Nostoc incubated with [¹³N]N₂ in the presence of MSX. The results of these experiments indicated that, in situ, symbiotic Nostoc assimilated about 10% of the N₂-derived NH ₄ ⁺ and that NH ₄ ⁺ was made available to Anthoceros tissue where it was apparently assimilated by the GS-GOGAT pathway. Since less than 1% of the fixed N₂ was lost to the suspension medium, it appears that transfer of NH ₄ ⁺ from symbiont to host tissue was very efficient in this extracellular symbiotic association.Abbreviations DON 6-diazo-5-oxo-l-norleucine - GDH glutamate dehydrogenase - GOGAT glutamate synthase - GS glutamine synthetase - MSX l-methionine-dl-sulfoximine     

N2-fixation in Erwinia herbicola

Four from 18 strains of Erwinia herbicola tested had nitrogenase activity and grew with N₂ as sole source of nitrogen under strict anaerobic conditions with a doubling time of 20–24 h. Nitrogenase activity started only 96–120 h after transfer to a special medium maintained under anaerobic conditions. A ten fold increase in protein per culture found after the maximum nitrogenase activity of 80–130 nmol C₂H₄. mg protein^-1·min^-1 was accompanied by a fall in pH of the medium (20 mM phosphate buffer and in 125 mM Tris-buffer) from pH 7.2 to 5.4 or less, but only to 6.8 in 100 mM phosphate buffer. In all cases we found a sharp curtailing of nitrogenase activity 48 h after the maximum. The bacteria utilized only 35–50% of the nitrogen fixed for growth. Erwinia herbicola strains differed from two strains of Enterobacter agglomerans in being unable to fix nitrogen on agar surfaces exposed to air. Specific nitrogenase activity in Erwinia herbicola is compared with data reported for other Enterobacteriaceae and is found to be higher than that reported for Klebsiella pneumoniae, Enterobacter cloacae or Citrobacter freundii.     

Agrobacterium-mediated transformation of the ectomycorrhizal symbiont Laccaria bicolor S238N

The development of an efficient transformation system is required to alter the expression of symbiosis-regulated genes and to develop insertional mutagenesis in the ectomycorrhizal basidiomycete Laccaria bicolor S238N. Vegetative mycelium of this fungus was transformed by Agrobacterium tumefaciens-mediated gene transfer. The selection marker was the hygromycin resistance gene of Escherichia coli (hph) under the control of the gpd promoter from Agaricus bisporus and the CaMV 35S terminator as part of the T-DNA. PCR amplification of hph and Southern blot analyses showed that the genome of the hygromycin-resistant transformants contained the cassette. The latter proved mostly single copy and random integration of part of the transgene into the fungal genome. A. tumefaciens-mediated gene transfer should facilitate future development of insertional mutagenesis, targeted gene disruption and RNA interference technology in L. bicolor.     

N5, N10-methylenetetrahydromethanopterin dehydrogenase (H2-forming) from the extreme thermophile Methanopyrus kandleri

A bacterium tentatively classified as Arthrobacter strain Py1 being capable to degrade pyrrole-2-carboxylate as only source of carbon, nitrogen, and energy was isolated from soil. In contrast to many other N-heterocyclic compounds, growth of the isolate on pyrrole-2-carboxylate was not affected by molybdate or its specific inhibitor tungstate, indicating a molybdoenzyme-independent breakdown. The latter was initiated by a hydroxylation reaction catalyzed by a pyrrole-2-carboxylate oxygenase, which also exhibited an NADH-cytochrome c reductase activity. The pyrrole-2-carboxylate oxygenase reaction as examined in cell extracts depended on NADH, FAD, and pyrrole-2-carboxylate; the apparent K _m values were 44, 6, and 43 M, respectively. A degradation pathway for pyrrole-2-carboxylate is proposed which involves 5-hydroxy-pyrrole-2-carboxylate and 2-oxoglutarate.     

Effect of N fertilizer rate and soil pH on N efficiency in corn

Nitrogen (N) efficiency components and N accumulation parameters were determined for seven commercially available corn (Zea mays L.) hybrids grown on a Cecil sandy loam soil (Typic Hapludult) in the Southeasten U.S. The hybrids were grown in field plots at three soil pH levels (4.8, 5.5, and 6.6) and four N fertilizer rates (0.4, 1.8, 3.2, and 6.0, g plant⁻¹). Nitrogen uilitzation efficiency (grain yield/total N uptake) was significantly different among hybrids in both 1983 and 1984. Differences in N use efficiency (grain yield/N supply) and N uptake efficiency (total N uptake/N supply) ranged from 100.4 to 114.6 and from 1.62 to 1.90, respectively, in 1984. Nitrogen fertilizer rate significantly affected all measured N accumulation and efficiency parameters except N uptake after silking in 1983. The results indicate that improving N uptake or soil N availability might increase grain yields for hybrids with higher N utilization efficiency.     

Two monoclonal antibodies highly specific for the blood group N determinant

Two monoclonal IgM antibodies, 179K and 35/5F, obtained following immunization of mice with A₂,MN or O,MN human erythrocytes, agglutinate NN and MN red cells strongly, and MM erythrocytes weakly. As shown by hemagglutination inhibition and solid phase ELISA, both antibodies are highly specific for the blood group N determinant. They react with N glycoprotein, its amino-terminal glycopeptides and with Ss glycoprotein (glycophorin B), which carries the blood group N determinant. They fail to react with M glycoprotein, M glycoprotein-derived glycopeptides, or with internal glycopeptides derived from N glycoprotein. Reaction of the antibodies with N glycoprotein is abolished by desialylation, periodate oxidation/borohydride reduction, orN-acetylation of the glycoprotein. Thus, the antibodies are specific for an epitope which includes sialylated oligosaccharide chain(s) and is located in the region of the amino-terminal leucine residue of N glycoprotein. MMU^– erythrocytes, lacking both blood group N and Ss glycophorin are non-reactive. Agglutination of MMU⁺ erythrocytes by the anti-N antibodies occursvia interaction with glycophorin B and correlates with the Ss phenotype of red cells MM,S erythrocytes are usually more strongly, agglutinated than MM,ss cells. The agglutination of MM erythrocytes decreases markedly as the pH is increased from 6 to 8, while agglutination of NN red cells is much less affected by shifts in pH over this range. As a result, both monoclonal antibodies are highly anti-N specific typing reagents when the agglutination assay is carried out at pH 8.     

Studies on the availability of Azolla N and urea N for rice growth using 15N

Field experiments (20 m² plots) were conducted to compare Azolla and urea as N sources for rice (Oryza sativa L.) in both the wet and dry seasons. Parallel microplot (1 m²) experiments were conducted using ¹⁵N. A total of approximately 60 kg N ha^-1 was applied as urea, Azolla, or urea plus Azolla. Urea or Azolla applied with equal applications of 30 kg N ha^-1 at transplanting (T) and at maximum tillering (MT) were equally effective for increasing rice grain yields in both seasons. Urea at 30 kg N ha^-1 at T and Azolla 30 kg N ha^-1 at MT was also equally effective. Urea applied by the locally recommended best split (40 kg at T and 20 kg at MT) gave a higher yield in the wet season, but an equal yield in the dry season. The average yield increase was 23% in the wet season, and 95% in the dry season. The proportion of the N taken up by the rice plants which was derived from urea (%NdfU) or Azolla (%NdfAz) was essentially identical for the treatments receiving the same N split. Recovery of ¹⁵N in the grain plus straw was also very similar. Positive yield responses to residual N were observed in the succeeding rice crop following both the wet and dry seasons, but the increases were not always statistically significant. Recovery of residual ¹⁵N ranged from 5.5 to 8.9% for both crops in succeeding seasons. Residual recovery from the urea applications was significantly higher than from Azolla in the crop succeeding the dry season crop. Azolla was equally effective as urea as an N source for rice production on a per kg N basis.