Effect of nitrogen form on the growth and nitrate concentration of lettuce

Summary A pot experiment with lettuce involving three N forms each at six application levels, showed that lettuce can be grown satisfactorily with a very low nitrate content when supplied with ammonium sulphate and a nitrification inhibitor. For plants growing on nitrate N, the optimum midrib sap nitrate concentration as maturity approached was about 1400 mg/1 NO₃-N. Large losses of mineral N were observed from the peat medium, even in the absence of plants. A relationship is presented which would enable a lettuce grower to estimate whole-shoot nitrate concentration from a quick test of midrib sapi.e. NO₃-N (mg/kg in fresh shoot) =0.14×NO₃-N (mg/l in sap). Tipburn was worst at intermediate levels of applied N, and was less serious with pure ammonium nutrition than with nitrate.     

Production and response to interleukin 2 in vitro and in vivo after bone marrow transplantation in mice

Lymphoid cells from bone marrow radiation chimeras do not produce normal levels of IL 2 but are capable of responding to IL 2 in mitogenic and cytotoxic assays in vitro. The administration of recombinant human IL 2 into host mice that have received allogeneic, H-2-compatible marrow did not enhance mortality.     

On the population dynamics and ecology of the shrimp species (Crustacea,Decapoda, Natantia) in the Central Amazonian river Tarumã-Mirim

Summary Collections over four years in the habitat of submerged litter show that shrimps are abundant the year round. Mean densities vary from 5–45 animals/m² of litter habitat. Finegrained density distribution within litter sites is highly clumped, but coarse-grained distribution in any given month between litter sites along the river is grosso-modo random.Density and species distribution are a function of the annual cycles of inundations. Of the five species (of a total of seven in the area) that were found to be breeding in the litter habitat it could be established that reproduction is restricted to the period of rising and highest water levels. Reproduction is low in all species, namely below 20 eggs per egg batch with essentially a single generation per year.Breeding ecology in relation to the litter habitat is briefly discussed.This project was supported jointly by the CNPq (Brasilian Research Council), by the OAS (Organization of the American States) and by the SUFRAMA (Financing body of local government)     

The finding of Enterobius vermicularis eggs in pre-Columbian human coprolites

Enterobius vermicularis eggs were found in human coprolites collected in the archaeological site of Caserones, Tarapaca Valley, Chile, dating from 400 BC to 800 AD. The human pinworm had already been found in other pre-historic archaeological sites in America, and its introduction in this continent is discussed.     

Trypanosoma cruzi: inhibition of host cell uptake of infective bloodstream forms by alpha-2-macroglobulin

The infection of murine macrophages and fibroblasts by recently isolated infective bloodstream trypomastigotes of Trypanosoma cruzi is inhibited by the addition of human plasma protease inhibitor alpha-2-macroglobulin (alpha 2M) or of soybean trypsin inhibitor. The ingestion of the non-infective epimastigotes by macrophages is not affected by the physiological protease inhibitor. Incubation of bloodstream trypomastigotes for 20 h in a serum-free axenic medium enhances their ability to infect macrophages in a process influenced by the temperature and sensitive to alpha 2M. After this period the infectivity of the parasites to cells was not sensitive to alpha 2M. These observations suggest that proteases located on the surface and/or secreted by the bloodstream trypomastigote form of T. cruzi may modulate its ability to infect host cells.     

Spectral sensitivity of photoreceptors in insect compound eyes: Comparison of species and methods

Summary Three different methods were used to determine the spectral sensitivity of retinula cells in the compound eyes of three species of hymenopteran insects (Apis mellifera, Melipona quadrifasciata, Osmia rufa). The conventional flash method gives the least reliable results. Sensitivity is extremely sensitive to small fluctuations of the resting potential and long lasting changes induced by preceding test flashes. The ramp method, which speeds up a spectral scan to about 1 min and keeps effective illumination constant at every flash, determines S() much more reliably. The best results are obtained with the spectral scan method, which provides the experimenter with aS() function of high spectral resolution within 20 s. Using this method we demonstrate that the high observed variability inS() of individual receptors is the result of the inadequacy of the flash method, which was the only method used in earlier studies.Double microelectrode experiments and variations of the stimulus conditions reveal that field potentials and return flow of electric current produced by activated neighboring cells have no effect in the bee eye. We conclude that the model of Shaw (1975, 1981) of current flow in the locust and fly eye does not apply to the bee eye. Very rare recordings (about 1%) of UV receptors with hyperpolarizing responses to long wavelength light are interpreted as having a synaptic inhibitory connection to green receptors.The improvement of spectral measurements of single receptors allows us for the first time to model the spectral input to a color-coding network with great precision.     

Leishmania mexicana amazonensis: Surface charge of amastigote and promastigote forms

The surface charge of Leishmania mexicana amazonensis was evaluated by means of the binding of colloidal iron hydroxyde particles at pH 1.8 and cationized ferritin particles at pH 7.2 to the cell surface, visualizated by electron microscopy and by direct measurements of the electrophoretic mobility of cells suspended in solutions of different pH. The following forms of the parasite were analysed: amastigotes (surrounded or not by the membrane of the endocytic vacuole, isolated from lesions), transitional forms, and infective (5 passages) and noninfective (176 passages) promastigotes. The results obtained indicate that the surface of L. m. amazonensis contains both negatively and positively charged dissociating groups and that changes occur in the surface charge during amastigote-promastigote transformation. Treatment of the parasite with neuraminidase significantly reduced the electrophoretic mobility of the cells. Neuraminidase-treated cells recovered their normal electrophoretic mobility when incubated for 8 hr in fresh culture medium by a process that is inhibited by puromycin.     

Residual beta-cell function in type II diabetes and evaluation of the hepatic insulin extraction

Insulin and C-peptide (free insulin and C-peptide in insulin-treated patients) were measured after glucose stimulation in nine Type II diabetics on chlorpropamide, eleven insulin-treated maturity-onset diabetics and in 8 normal controls. Dissociation between C-peptide and insulin response to glucose was observed in several diabetics. The relation between incremental molar areas under C-peptide and insulin curves, after glucose challenge (delta CPR - delta IRI/delta CPR) were used to evaluate the hepatic insulin extraction in all but the insulin-treated diabetics. The lower insulin requirements and better control of the short-duration insulin-treated maturity-onset diabetics in relation to the long-term ones could not be explained either by the residual insulin secretion or by the level of "insulin antibodies". The chlorpropamide-responsive patients presented higher insulin levels after the glucose challenge and a lower hepatic insulin extraction than the non-responsive ones.