Influence of inorganic nitrogen and pH on the elongation of maize seminal roots

BACKGROUND AND AIMS

Root absorption and assimilation of inorganic nitrogen usually alters rhizosphere pH, but the immediate influence of such pH changes on root elongation as well as that of exogenous inorganic nitrogen itself has been uncertain.

METHODS

A differential extensiometer that monitored on a real-time, continuous basis root elongation in an intact 3-d-old maize plant was developed. Treatments included root media at pH 6.5 or 5.6 that lacked nitrogen and ones at pH 6.5 that contained 100 mmol m(-3) NH(4)(+) or NO(3)(-).

KEY RESULTS

Acidifying the root medium from pH 6.5 to 5.6 nearly doubled the elasticity of the seminal root, but slightly decreased its elongation. Plasticity of the root apex was not detectable in all treatments. The presence of ammonium or nitrate in the medium stimulated elongation by 29 % or 14 %, respectively. Addition of an osmoticum to the medium had no effect on root elongation in the absence of inorganic nitrogen, but diminished the stimulation of elongation in the presence of ammonium and nitrate. This indicates that these ions or their by-products serve partially as osmolytes.

CONCLUSIONS

In nutrient solution, root elongation of a maize seedling--even one with ample nitrogen reserves--depended most strongly on exogenous inorganic nitrogen, and less so, if at all, on either the pH of the bulk nutrient solution or the mechanical properties of cell walls.

The potential for nitrification and nitrate uptake in the rhizosphere of wetland plants: a modelling study

BACKGROUND AND AIMS

It has recently found that lowland rice grown hydroponically is exceptionally efficient in absorbing NO3-, raising the possibility that rice and other wetland plants growing in flooded soil may absorb significant amounts of NO3- formed by nitrification of NH4+ in the rhizosphere. This is important because (a) this NO3- is otherwise lost through denitrification in the soil bulk; and (b) plant growth and yield are generally improved when plants absorb their nitrogen as a mixture of NO3- and NH4+ compared with growth on either N source on its own. A mathematical model is developed here with which to assess the extent of NO3- absorption from the rhizosphere by wetland plants growing in flooded soil, considering the important plant and soil processes operating.

METHODS

The model considers rates of O2 transport away from an individual root and simultaneous O2 consumption in microbial and non-microbial processes; transport of NH4+ towards the root and its consumption in nitrification and uptake at the root surface; and transport of NO3- formed from NH4+ towards the root and its consumption in denitrification and uptake by the root. The sensitivity of the model's predictions to its input parameters is tested over the range of conditions in which wetland plants grow.

KEY RESULTS

The model calculations show that substantial quantities of NO3- can be produced in the rhizosphere of wetland plants through nitrification and taken up by the roots under field conditions. The rates of NO3- uptake can be comparable with those of NH4+. The model also shows that rates of denitrification and subsequent loss of N from the soil remain small even where NO3- production and uptake are considerable.

CONCLUSIONS

Nitrate uptake by wetland plants may be far more important than thought hitherto. This has implications for managing wetland soils and water, as discussed in this paper.

Increased endothelin activity mediates augmented distal nephron acidification induced by dietary protein

We tested the hypothesis that increased dietary protein augments distal nephron acidification through an endothelin-dependent mechanism. Munich-Wistar rats ate minimum electrolyte diets of 50% (HiPro) and 20% (CON) casein-provided protein, the latter comparable to standard chow. HiPro vs. CON had higher distal nephron H+ secretion (41.3 +/- 4.0 vs. 23.0 +/- 2.1 pmol/mm.min, p < 0.002) mediated by augmented Na+/H+ exchange and H(+)-ATPase activity. Renal cortex of HiPro vs. CON had higher ET-1 addition to microdialysate and higher ET-1 mRNA, consistent with increased renal ET-1 production. Bosentan, an endothelin A/B receptor antagonist, decreased HiPro distal nephron H+ secretion (28.4 +/- 2.4 vs. 41.3 +/- 4.0 pmol/mm.min, p < 0.016) through decreased Na+/H+ exchange and decreased H(+)-ATPase activity. Increased dietary protein augments distal nephron acidification through an endothelin-sensitive increase in Na+/H+ exchange and H(+)-ATPase activity, supporting an endothelin role in the distal nephron response to this common challenge to acid-base status.

Human Rhesus-associated glycoprotein mediates facilitated transport of NH(3) into red blood cells

Rhesus (Rh) antigens are carried by a membrane complex that includes Rh proteins (D and CcEe), Rh-associated glycoproteins (RhAG), and accessory chains (LW and CD47) associated by noncovalent bonds. In heterologous expression systems, RhAG and its kidney orthologs function as ammonium transporters. In red blood cells (RBCs), it is generally accepted that NH(3) permeates by membrane lipid diffusion. We have revisited these issues by studying RBC and ghosts from human and mouse genetic variants with defects of proteins that comprise the Rh complex. In both normal and mutant cells, stopped-flow analyses of intracellular pH changes in the presence of inwardly directed methylammonium (CH(3)NH(+)(3)+CH(3)NH(2)) or ammonium (NH(+)(4)+NH(3)) gradients showed a rapid alkalinization phase. Cells from human and mouse variants exhibited a decrease in their kinetic rate constants that was strictly correlated to the degree of reduction of their RhAG/Rhag expression level. Rate constants were not affected by a reduction of Rh, CD47, or LW. CH(3)NH(2)/NH(3) transport was characterized by (i) a sensitivity to mercurials that is reversible by 2-mercaptoethanol and (ii) a reduction of alkalinization rate constants after bromelain digestion, which cleaves RhAG. The results show that RhAG facilitates CH(3)NH(2)/NH(3) movement across the RBC membrane and represents a potential example of a gas channel in mammalian cells. In RBCs, RhAG may transport NH(3) to detoxifying organs, like kidney and liver, and together with nonerythroid tissue orthologs may contribute to the regulation of the systemic acid-base balance.

Interrelationships between the pathways of inorganic nitrogen assimilation in the cyanobacterium Gloeothece can be described using a mechanistic mathematical model

•  A mathematical model is described that simulates the major features of the interactions between different nitrogen (N)-sources in the nonheterocystous diazotrophic cyanobacterium Gloeothece. •  The interaction between ammonium and nitrate is related to the intracellular concentration of glutamine (GLN), which in turn is representative of cellular N-status. Development of nitrogenase activity is related to N-limitation but, once developed, continues for as long as there is sufficient glucan (carbon-reserve) in order to support N₂ fixation and the assimilation of the resultant ammonium into amino acids. •  Nitrogenase activity decreases in response to elevated N-status and also to increased net oxygen evolution, in keeping with biochemical reality. The model describes the diel cycle of C and N₂ fixation as seen under alternating 12 h light and 12 h darkness, and also the N₂ fixation cycle of about 40 h duration seen in cells cultured in continuous illumination. •  This model has the potential to be adapted to describe N₂ fixation in heterocystous cyanobacterium and in Trichodesmium.

Physiological and growth responses of the montane bryophyte Racomitrium lanuginosum to atmospheric nitrogen deposition

•  The effects of nitrogen (N) deposition on the moss Racomitrium lanuginosum within montane heath in Scotland were investigated over 5 yr. •  Permanent field plots were sprayed with KNO₃ or NH₄ Cl solutions, at doses equivalent to 10 and 40 kg N ha^-1  yr^-1 , in 3-6 applications each summer. •  Racomitrium growth and cover were severely reduced by N addition, whilst the proportion of dead shoots greatly increased. N dose decreased inducibility of shoot nitrate reductase activity (NRA), suggesting that N saturation of Racomitrium occurred, and caused an increase in potassium leakage. At high dosage, effects of NH₄ ⁺ were more detrimental than NO₃ ^- . •  Physiological responses to N indicate that the habitat's critical load (CL) is exceeded by addition of 10 kg N ha^-1  yr^-1 . The differential toxicity of the two forms of N suggests that predominant ion type in deposition should be taken into consideration when CLs are set. In contrast to tissue N, NRA correlated well with shoot growth, and may thus be a useful biological indicator of moss condition.

Subcellular NH4 + flux analysis in leaf segments of wheat (Triticum aestivum)

•  We report the first use of tracer ¹³ NH₄ ⁺ (¹³ N-ammonium) efflux and retention data to analyse subcellular fluxes and compartmentation of NH₄ ⁺ in the leaves of a higher plant (wheat, Triticum aestivum). •  Leaf segments, 1-2 mm, were obtained from 8-d-old seedlings. The viability of the segments, and stability of NH ₄ ⁺ acquisition over time, were confirmed using oxygen-exchange and NH ₄ ⁺ -depletion measurements. Fluxes of NH ₄ ⁺ and compartment sizes were estimated using tracer efflux kinetics and retention data. •  Influx and efflux across the plasma membrane, half-lives of exchange and cytosolic pool sizes were broadly similar to those in root systems. As the external concentration of NH ₄ ⁺ ([NH ₄ ⁺ ] _o ) increased from 10 µ m to 10 m m , both influx and efflux greatly increased, with a sixfold increase in the ratio of efflux to influx. Half-lives were similar among treatments, except at [NH ₄ ⁺ ] _o  = 10 m m , where they declined. Concentrations of NH ₄ ⁺ in the cytosol ([NH ₄ ⁺ ] _c ) increased from 2.6 to 400 m m . •  Although [NH ₄ ⁺ ] _c became large as [NH ₄ ⁺ ] _o increased, the ratio of [NH ₄ ⁺ ] _c to [NH ₄ ⁺ ] _o decreased more than sixfold. The apparently futile cycling of NH ₄ ⁺ at high [NH ₄ ⁺ ] _o suggested by the large fluxes of NH ₄ ⁺ in both directions across the membrane indicate that leaf cells respond to potentially toxic NH ₄ ⁺ concentrations in a manner similar to root cells.

The large capacity for dark nitrate-assimilation in diatoms may overcome nitrate limitation of growth

•  The ability of the diatom Thalassiosira weissflogii to assimilate inorganic N in darkness is compared with that seen in flagellates. •  Experiments were conducted with T. weissflogii grown in N-replete and in N-limiting cultures and the rates and capacity for ammonium and nitrate assimilation were determined. •  High daily growth rates in the diatom under high-light nitrate-replete conditions are only attainable by continuing nitrate assimilation in darkness using excess C accumulated in the light when nitrate assimilation cannot match C-fixation. The ability to use ammonium in darkness is greater than for nitrate but the ratio of dark to light assimilation for each N source is similar over a wide range of cellular N : C ratios. These capabilities are in strong contrast with those in the flagellates Heterosigma carterae and Heterocapsa illdefina, which are incapable of high nitrate use in darkness. •  While the possession of large capacity for dark nitrate-assimilation in diatoms may provide a mechanism that overcomes nitrate limitation of growth, the explanation for the lower capabilities exhibited by flagellates is less clear.

Modelling suggests that optimization of dark nitrogen-assimilation need not be a critical selective feature in phytoplankton

•  Alternative strategies for the dark assimilation of ammonium and nitrate into microalgae are explored using a mechanistic model of algal physiology. •  The standard diatom strategy, continuation of N assimilation at high rates in darkness as long as reserve C remains, is the most advantageous. The flagellate strategy, incorporating ammonium but not nitrate at a reasonable rate in darkness, is best suited to organisms with high metabolic costs, inhabiting waters with relatively high concentrations of ammonium. The strategy of vertically migrating diatoms - accumulation of nitrate in internal pools for assimilation after return to the photic zone - is best suited to slow-growing cells in low-ammonium environments. •  Differences between the strategies become less significant with increasing N-source limitation (the situation more typically encountered by flagellates and migratory species) because transport rather than post-transport assimilatory processes become most limiting. •  It is suggested that optimization of dark N-assimilation is not a critical selective feature; organisms with contrasting abilities in this regard usually inhabit different water bodies and have other more fundamental phenotypic differences (e.g. motility or silicon requirements).

Spatial distribution of nitrogen on grazed karst landscapes

The impact on water quality by agricultural activity in karst terrain is an important consideration for resource management within the Appalachian region. Karst areas comprise about 18% of the region"s land area. An estimated one-third of the region"s farms, cattle, and agricultural market value are located on karst terrain. Mean nitrate concentrations in several karst springs in southeastern West Virginia exhibit a strong linear relationship with the percentage of agriculture land cover. Development of best management practices for efficient nitrogen (N) use and reduction of outflow of N to water from karst areas requires knowledge about N dynamics on those landscapes. Water extractable NO3-N and NH4-N were measured along transects at four soil depths in two grazed sinkholes and one wooded sinkhole. Distribution of soil NO3-N and NH4-N were related to frequency of animal presence and to topographic and hydrologic redistribution of soil and fecal matter in the grazed sinkholes. Karst pastures are characterized by under drainage and funneling of water and contaminants to the shallow aquifer. Control of NO3-N leaching from karst pasture may depend on management strategies that change livestock grazing behavior in sinkholes and reduce the opportunity for water and contaminants to quickly reach sinkhole drains.

Modeling of nitrogen in river water using a detailed and a simplified model

To model catchment surface water quantity and quality, different model types are available. They vary from detailed physically based models to simplified conceptual and empirical models. The most appropriate model type for a certain application depends on the project objectives and the data availability. The detailed models are very useful for short-term simulations of representative events. They cannot be used for long-term statistical information or as a management tool. For those purposes, more simplified (conceptual or meta-) models must be used. In this study, nitrogen dynamics are modeled in a river in Flanders. Nitrogen sources from agricultural leaching and domestic point sources are considered. Based on this input, concentrations of ammonium (NH4-N) and nitrate (NO3-N) in the river water are modeled in MIKE 11 by taking into consideration advection and dispersion and the most important biological and chemical processes. Model calibration was done on the basis of available measured water quality data. To this detailed model, a more simplified model was calibrated with the objective to more easily yield long-term simulation results that can be used in a statistical analysis. The results show that the conceptual simplified model is 1800 times faster than the MIKE 11 model. Moreover the two models have almost the same accuracy. The detailed models are recommended for short-term simulations unless there are enough data for model input and model parameters. The conceptual simplified model is recommended for long-term simulations.

Inorganic and organic losses of nitrogen from upland regions of Britain: concentrations and fluxes

The nitrogen (N) composition of streams draining eight upland regions of Britain was compared using monthly samples collected between April 1997 and April 1998. Stream samples were analysed for total N (TN), particulate N (PN), nitrate (NO3), ammonium (NH4), and dissolved organic nitrogen (DON). Concentrations of TN were small, generally less than 1.5 mg N l(-1), were dominated by dissolved forms of N, and varied significantly between regions. NO3 accounted for the majority of variability. Concentrations of DON also varied between regions but to a smaller extent than those of NO3. There were considerable variations in TN fluxes between upland regions, which ranged between 3.8 and 16.1 kg N ha(-1) year(-1). The majority of the variation was due to NO3 fluxes, which were largest in regions receiving largest inputs of atmospheric N deposition and ranged between 1.4 and 13.5 kg N ha(-1) year(-1). Fluxes of DON ranged between 1 and 3.5 kg N ha(-1) year( -1), while fluxes of PN were generally less than 0.5 kg N ha(-1) year(-1) , and NH4 fluxes ranged between 0.1 and 0.4 kg N ha(-1) year(-1). NO3 was the dominant fraction (47-84%) of N exported from all upland regions except the Highlands, where DON accounted for 52% of the TN flux. This study has shown that the DON fraction is an important component of the total N transported by upland streams in Britain.

Monitoring nitrogen leaching for the evaluation of the Dutch minerals policy for agriculture in clay regions

This paper presents the results of the Dutch monitoring program for agriculture in the clay regions for the period 1996-2000 and evaluates the monitoring strategy. A wide range of farms (25 to 85%) had a NO3--N concentration in tile drainwater higher than the EU standard of 11.3 mg/l. The low figure is related to wet winters; the high, to dry winters. Arable farms are more prone to NO3- leaching than dairy farms. On arable farms, about 25% of the N surplus leached to groundwater and tile drainwater, on dairy farms this was about 15%. N in tile drainwater has shown to be the best indicator for monitoring the effects of farming practice changes in the clay regions. The average NO3--N concentration in tile drainwater was 18.8 and 3.2 mg/l in borehole water on farms where both were monitored. It is known that N use has a relationship with NO3- in tile drainwater and not with NH4+ and organic N. The presented results indicate that crop rotation and precipitation strongly influence NO3- concentration in tile drainwater.

Links between genetic and functional diversity - a bridge too far?

The view that nutrient acquisition by most plants growing in natural ecosystems is mediated by mycorrhiza-forming symbiotic fungi is now largely accepted. With this perception comes the need to learn more about the identity of the organisms responsible for these key processes. Herein lies a challenge taken up by Vrålstad et al. on pp. 549-563 in this issue.

Comparative kinetic analysis of ammonium and nitrate acquisition by tropical lowland rice: implications for rice cultivation and yield potential

Nitrogen limitation compromises the realization of yield potential in cereals more than any other single factor. In rice, the world's most important crop species, the assumption has long been that only ammonium-N is efficiently utilized. Consequently, nitrate utilization has been largely ignored, although fragmentary data have suggested that growth could be substantial on nitrate. Using the short-lived radiotracer ¹³ N, we here provide direct comparisons of root transmembrane fluxes and cytoplasmic pool sizes for nitrate- and ammonium-N in a major variety of Indica rice (Oryza sativa), and show that nitrate acquisition is not only of high capacity and efficiency but is superior to that of ammonium. We believe our results have implications for rice breeding and molecular genetics as well as the design of water-management and fertilization regimes. Potential strategies to harness this hitherto unexplored N-utilization potential are proposed.

The influence of nitrogen fertilization on the carbon economy of Paxillus involutus in ectomycorrhizal association with Betula pendula

Mycorrhizal mycelium was allowed to grow into a compartment from which roots were excluded. Ammonium or nitrate was supplied exclusively to the fungus and the respiration rate before and after nitrogen addition was measured. Mycelial respiration in the fungal compartment represented 11-29%, of total fungal and root respiration. The mycelium in the fungal compartment received 20-29% of shoot net assimilation, and 43-64%, of the carbon allocated to the mycelium was respired. The nitrogen-induced respiration increase ranged, in the fungal compartment, from 54 to 180%.

Colonic protein fermentation and promotion of colon carcinogenesis by thermolyzed casein

Thermolyzed casein is known to promote the growth of aberrant crypt foci (ACF) and colon cancer when it is fed to rats that have been initiated with azoxymethane. We speculated that the promotion was a consequence of increased colonic protein fermentation (i.e., that the thermolysis of the casein decreases its digestibility, increases the amount of protein reaching the colon, and increases colonic protein fermentation and that the potentially toxic products of this fermentation promote colon carcinogenesis). We found that the thermolysis of casein reduces its digestibility and increases colonic protein fermentation, as assessed by fecal ammonium and urinary phenol, cresol, and indol-3-ol. Thermolysis of two other proteins, soy and egg white protein, also increases colonic protein fermentation with increased fecal ammonia and urinary phenols, and thermolysis of all three proteins increases the levels of ammonia and butyric, valeric, and i-valeric acids in the cecal contents. We found, however, that the increased protein fermentation observed with thermolysis is not associated with promotion of colon carcinogenesis. With casein, the kinetics of protein fermentation with increasing thermolysis time are clearly different from the kinetics of promotion of ACF growth. The formation of the fermentation products was highest when the protein was thermolyzed for one hour, whereas promotion was highest for protein that had been thermolyzed for two or more hours. With soy and egg white, thermolysis increased colonic protein fermentation but did not promote colon carcinogenesis. Thus, although thermolysis of dietary casein increases colonic protein fermentation, products of this fermentation do not appear to be responsible for the promotion of colon carcinogenesis. Indeed, the results suggest that protein fermentation products do not play an important role in colon cancer promotion.

Regulation of nitrate reductase in the ectomycorrhizal basidiomycete, Hebeloma cylindrosporum Romagn., cultured on nitrate or ammonium

The growth of Hebeloma cylindrosporum Romagn. on nitrate medium is associated with nitrate reductase activity equivalent to that measured in herbaceous angiosperms. Nitrate is not indispensable for the induction of NR, as thalli cultivated in ammonium have the same NR activity as thalli cultured on nitrate. However, the simultaneous presence in the culture medium of ammonium with an organic acid such as malate, citrate or succinate causes a diminution of NR activity. Glutamine or asparagine, by-products in the assimilation of ammonium and malate, could intervene in the regulation of this enzyme. The data suggest that the absence of nitrogen or the presence of a nitrogen source, such as ammonium, inappropriate for growth derepresses nitrate reductase in this fungus.

Ammonium assimilation by the nitrate-utilizing yeast, Candida nitratophila

Ammonium-nitrogen was assimilated rapidly by nitrogen-replete cultures of the nitrate-utilizing yeast, Candida nitratophila as long as a suitable source of carbon was available. These cultures contained high activities of an NADPH-dependent glutamate dehydrogenase with a relatively high affinity for ammonium (K_m = 0.27 mM) and high glutamine synthetase activity. Both enzyme activities were apparently derepressed when glutamine-grown cultures were starved of nitrogen or transferred to nitrate medium. Nitrogen-deficient cultures also contained NADH-dependent glutamate synthase activity that was inhibited by azaserine in vitro. Ammonium assimilation in vivo, was inhibited by methionine sulphoximine whilst addition of azaserine resulted in an accumulation of intracellular glutamine and an inhibition of glutamate production. Our results suggest that, in C. nitratophila, there is a potential for ammonium assimilation via both the glutamate dehydrogenase pathway and the glutamine synthetase/glutamate synthase pathway with the latter pathway predominating in nitrogen-deficient cells.

Acidification and endosome-like compartments in the presynaptic terminals of frog retinal photoreceptors

By using the 'acidotropic' vital dye, Acridine Orange, we have found that the presynaptic terminals of rod and cone photoreceptors in retinas of Rana pipiens maintain a low pH relative to the surrounding medium through an energy dependent mechanism. When this pH is raised, by exposing the retinas to weak bases like ammonium chloride, the terminals exhibit large, membrane-delimited compartments, many of which accumulate endocytic tracers. This effect is partly reversed when the weak bases are removed. We infer that among the acidified structures within the terminals are endocytic compartments with at least some of the characteristics of the endosomes that participate in receptor-mediated endocytosis in other cell types. One role of these structures in the terminals may be in the recycling of synaptic vesicles.

EFFECT OF NITROGEN FEEDING SOURCE ON THE SUPPLY OF NITROGEN FROM ROOT TO SHOOT AND THE SITE OF NITROGEN ASSIMILATION IN MAIZE (ZEA MAYS L. CV. R201)

Maize plants (Zea mays L. cv. R201) were grown to 21 d in pH-controlled gravel culture with 2 mM inorganic N supplied as nitrate alone, ammonium alone or 1:1 nitrate + ammonium. At 21 d, the ¹⁴ N feeding solutions were replaced with ¹⁵ N solutions, and xylem sap collections were made 4 and 8 h after the commencement of feeding. Leaf and root material was harvested also for in vitro nitrate reductase and glutamine synthetase activity assays. Xylem sap analyses showed that in nitrate-only fed plants the major supply of nitrogen from root to shoot was in the nitrate form (60%) with 35 % carried as amino compounds. However, 93% of ¹⁵ N was transported to the shoot as nitrate and only 6% in amino compounds, indicating the more direct routing of newly absorbed nitrogen to the shoot via the former. Leaf NRA was seven-fold greater than that of the root, confirming the shoot as the major site of nitrogen assimilation in plants fed only nitrate. In ammonium-only fed plants, 84% of xylem N was found in organic form (66%¹⁶ N), the remainder translocating as ammonium, identifying the root as the major site of ammonium N assimilation. In ammonium + nitrate fed plants, 64% of xylem N was present as organic N (55%¹⁶ N), 34% as nitrate (43 %¹⁶ N), indicating shared N assimilation between shoot and root, with root assimilation predominating. In plants receiving nitrate, glutamine was the major N compound translocated, in plants receiving only ammonium, asparagine predominated. GS activity was approximately the same in root and shoot and showed no response to N source. The significance of these results is discussed with respect to the reported increased productivity of maize fed a mixed nitrate-ammonium N source.

Development of a Standard Reference Material for Rainwater Analysis

This paper describes the development of Standard Reference Material, SRM 2694, "Simulated Rainwater," intended to aid in the analysis of acidic rainfall. Details of the formulation and preparation of the two levels of solutions (2694-I and 2694-II) are given. The 10 analytical techniques used to measure the 12 components in the solutions are described in brief. The data used in the statistical evaluation of the results are summarized and the recommended values for pH, specific conductance, acidity, fluoride, chloride, nitrate, sulfate, sodium, potassium, ammonium, calcium, and magnesium are tabulated. The instability of ammonium ion in acidic solutions is discussed. Recommendations for the use of SRM 2694, particularly with regard to the measurement of pH, are given.

Tumour inhibitory effects of TCGF/IL-2/-containing preparations

Supernatants from ConA-stimulated rat spleen cell cultures and from cultures of PMA-stimulated murine lymphoma subline EL-4TF were found to contain TCGF and to inhibit growth of a transplantable, MC-induced sarcoma MC11 in syngeneic mice. Tumour-inhibitory effects of the supernatants were dependent on local and repeated administration. Prior to use of the supernatants obtained from PMA-stimulated EL-4TF cell cultures, the dialysable PMA had to be removed; contamination with PMA was found to abolish the tumour-inhibitory effect of the supernatants and to produce enhancement of tumour growth. A significant tumour-inhibitory effect has also been obtained with partially purified TCGF prepared from culture supernatants of cloned EL-4TF cells by ammonium sulphate precipitation, ion-exchange (FPLC) chromatography, and AcA 44 Ultrogel filtration.

Influence of Potassium and Nitrogen Fertilization on Parasitism by the Root-knot Nematode Meloidogyne javanica

The influence of various c oncentrations of K, nitrogen sources, and inoculation with root-knot nematode Meloidogyne javanica were evaluated in tomato plants. Increased potassium concentration increased top and root fresh weights of intact plants and fresh weights of excised roots. Nitrate-fertilized plants weighed more than plants receiving ammonium independent of the K level in the medium. Nematode counts on roots were not affected by nutritional differences in intact or excised roots. In intact roots a high percentage of males was recorded at low K levels, whereas in excised roots the proportion of males in the population rose as the K levels increased. Inoculated intact roots accumulated K when the level of potassium supply was low; infected excised roots contained less K than did nematode-free roots.

Antigens in immune complexes from patients with breast cancer. Identification of autoantigens in immune complexes isolated from breast cancer effusions

Sera and effusion fluids of patients with breast cancer (BC) contain immune complexes (IC). Antigens present in these complexes were isolated as follows: a pool of effusions from patients with BC was fractionated with ammonium sulfate. The proteins precipitating at 40% saturation were further fractionated by filtration through a Sephadex G-200 column. The material recovered in the first peak (molecules larger than monomeric IgG) was brought to pH 3.0 to dissociate the IC, and the mixture was filtered through a column of Sephacryl S-300 at pH 3.0. Proteins smaller than monomeric IgG were collected, radioiodinated, and used as antigens (125Ag) to search for corresponding antibodies in sera of patients with BC (BCS) and of healthy individuals (NHS). 125Ag was reacted with the sera and the immune complexes obtained were precipitated with an antiserum to human Ig and analyzed by SDS-polyacrylamide gel electrophoresis followed by autoradiography. Both NHS and BCS contained antibodies against two antigens; one of these appeared as a strong band of 17KD, the other as a doublet of approximately 25KD. It is concluded that some of the proteins in the IC from patients with BC are auto-antigens. No BC-specific antigens were identified.