Evidence for a periodic excretion of nitrogen by roots of grass-legume associations

Diurnal variation in ion content of the solution bathing roots of two plants growing together in sand culture was analysed for three pairs of grass-legume species (Lolium multiflorum andTrifolium pratense; Zea mays andGlycine hispida; Avena sativa andVicia sativa) and their monospecific controls. Biomass and nitrogen content of plants were determined. Ion concentration (NO ₃ ⁻ , NO ₂ ⁻ , NH ₄ ⁺ , and K⁺) and pH of root solutions were measured for Lolium-Trifolium plant pairs and controls at 6 hours intervals over 36 h, starting at 8 am within a circadian cycle. Root solutions were regularly depleted in NO ₃ ⁻ by the grasses (Lolium-Lolium control) throughout the cycle. For associations involving the legume (Lolium-Trifolium and Trifolium-Trifolium), NO ₃ ⁻ depletion was followed by NO ₃ ⁻ enrichment at night, from late afternoon to early morning; the enrichment was more marked for the Lolium-Trifolium association. Solutions which did not contain NO ₂ ⁻ ions, were enriched by trace amounts of NH ₄ ⁺ ions, largely depleted in K⁺ and alkalanized for all associations throughout the cycle. Repeating the experiment with the three pairs of species at the vegetative phase of development confirmed the previous results: NO ₃ ⁻ enrichment during the night for associations with legumes. When the experiment was repeated with older plants which had almost completed their flowering stage, depletion only was observed and no NO ₃ ⁻ enrichment. These data suggest that NO ₃ ⁻ enrichment results from N excretion from active nodulated roots of the legume, accounting for the increase in both biomass and nitrogen content of the companion grass in grass-legume association. The quantitative importance and periodicity of nitrogen excretion as well as the origin of nitrate enrichment are discussed.     

Multielement analysis of biological samples by inductively coupled plasma-mass spectrometry

Interest in the biological behavior of a growing number of elements, along with increasing recognition of the importance of interactions among them, demands a versatile and reliable technique for multielement analysis of biological samples. Significant improvements over the sensitivity achieved with conventional inductively coupled plasma (ICP) optical emission spectrometries have been realized with the introduction of quadrupole mass spectrometry (MS) for detection of ions in the plasma. The hybrid technique of ICP-MS promises to be a method of rapid multielement analysis, at detection limits that approach or surpass those of other technologies. However, the application of ICP-MS to analyses of biological interest is truly in its infancy. Here we report the use of ICP-MS for the determination of more than 30 elements of biological interest in a tissue and a biological fluid (rat liver and serum, respectively). Experimental values of the elements serve as a basis for discussion of analytical protocols, performance criteria, and certain problems peculiar to ICP-MS.     

Propionate metabolism in a methanogenic enrichment culture. Direct reductive carboxylation and acetogenesis pathways

Abstract Serial dilutions of methanogenic sludges in propionate medium gave a methanogenic non-acetoclastic enrichment degrading 1 mol of propionate to 1.6 mol of acetate and 0.17 mol of methane, with a transient accumulation of butyrate. NMR recordings showed the conversion of [2-¹³C]- and [3-¹³C]-propionate to [3-¹³C]- and [4-¹³C]-butyrate, respectively, thus demonstrating a reductive carboxylation of propionate to butyrate. The labelling found in the accumulated acetate and fermentation balances also suggested that reductive carboxylation was the major pathway involved in propionate conversion to acetate.     

Coated nuts as an enrichment device to elicit tool use in tufted capuchins (Cebus apella)

The present paper describes a simple technique that hardens the shell of nuts and makes the use of a tool to crack them open more compelling. Walnuts were coated with a dough of sawdust and nontoxic white glue in different combinations; they were tested for hardness by using machines normally used to test different kinds of wood. Data on relative hardness for uncoated walnuts and walnuts coated with dough of two different combinations are presented. The coated walnuts were significantly harder to break than the uncoated ones, whereas no significant difference was found when comparing the hardness of two types of coated walnuts. Furthermore, observations on a captive group of tufted capuchins (Cebus apella) are described. The monkeys needed significantly more time to break open the coated walnuts. Early results show that coated walnuts may favor acquistion of tool use skills in a juvenile capuchin.     

The allometric approach to species differences in brain size

Allometric methods can be used to test quantitative theories of the relationship between brain size and body size across species, and to search for ecological, behavioural, life history, and ontogenetic correlates of brain size. Brain size scales with an allometric exponent of around 0.75 against body size across mammals, but is closer to 0.56 for birds and for reptiles. The slope of the allometric line often varies depending upon the taxonomic level of analysis. However, this phenomenon, at least in mammals, may be a statistical artifact. Brain size for a given body size (relative brain size) varies among orders in birds and mammals, and some dietary associations with relative brain size have been found in particular taxa. Developmental status at birth is the most consistent correlate of relative brain size: precocial neonates have larger brains for a given maternal size than altricial neonates in both birds and mammals. Altricial neonates, however, have more brain growth following birth, and in birds also have larger relative adult brain sizes. Energetic explanations for differences in neonatal brain growth, although attractive on theoretical grounds, have largely failed to stand up to empirical tests.     

The influence of CO2 enrichment, phosphorus deficiency and water stress on the growth, conductance and water use of Pinus radiata D. Don

Abstract. Seedlings of Pinus radiata D. Don were grown in growth chambers for 22 weeks with two levels of phosphorus, under either well-watered or water-stressed conditions at CO₂ concentrations of either 330 or 660mm³ dm^?3. Plant growth, water use efficiency and conductance were measured and the relationship between these and needle photosynthetic capacity, water use efficiency and conductance was determined by gas exchange at week 22. Phosphorus deficiency decreased growth and foliar surface area at both CO₂concentrations; however, it only reduced the maximum photosynthetic rates of the needles at 660 mm³ CO₂ dm^?3 (plants grown and measured at the same CO₂ concentration). Water stress reduced growth and foliar surface area at both CO₂ concentrations. Increases in needle photosynthetic rates appeared to be partly responsible for the increased growth at high CO₂ where phosphorus was adequate. This effect was amplified by accompanying increases in needle production. Phosphorus deficiency inhibited these responses because it severely impaired needle photosynthetic function. The relative increase in growth in response to high CO₂ was higher in the periodically water-stressed plants. This was not due to the maintenance of cell volume during drought. Plant water use efficiency was increased by CO₂ enrichment due to an increase in dry weight rather than a decrease in shoot conductance and, therefore, transpirational water loss. Changes in needle conductance and water use efficiency in response to high CO₂ were generally in the same direction as those at the whole plant level. If the atmospheric CO₂ level reaches the predicted concentration of 660 mm³ dm^?3 by the end of next Century, then the growth of P. radiata will only be increased in areas where phosphorus nutrition is adequate. Growth will be increased in drought-affected regions but total water use is unlikely to be reduced.     

Filtration rate capacities in 6 species of European freshwater bivalves

Summary Filtration rate capacities in undisturbed freshwater bivalves were determined by means of two different methods (indirect clearance and suction methods) in Anodonta anatina (L.), Unio tumidus Philipsson, Unio pictorum (L.), Unio crassus Philipsson, Dreissena polymorpha (Pallas) and Sphaerium corneum (L.). In A. anatina, D. polymorpha, and S. corneum the filtration rate (FR, 1 h^-1) at 19–20°C as a function of dry tissue weight (DW, g) or ash-free dry weight (AFDW, g) could be expressed by the equations: 1.10 DW^0.78, 6.82 DW^0.88, and 2.14 AFDW^0.92, respectively. In U. tumidus, U. pictorum, and U. crassus filtration rates were comparable with those of A. anatina. In D. polymorpha the b value of the corresponding regression of gill area on dry weight was 0.87. The rates of water transport in freshwater bivalves are 2–8 times lower than in marine bivalves of comparable size. A corresponding difference in the filtration rate per gill area unit is found. The measured filtration rates in undisturbed bivalves are substantially higher (at least 4 times) than previously reported. This indicates that the impact of bivalve water processing on freshwater ecosystems is greater than hitherto suggested.     

Effect of CO2 enrichment and nitrogen availability on resource acquisition and resource allocation in a grass,Bromus mollis

Summary The effects of CO₂ enrichment on the growth, biomass partitioning, photosynthetic rates, and leaf nitrogen concentration of a grass, Bromus mollis (C₃), were investigated at a favorable and a low level of nitrogen availability. Despite increases in root: shoot ratios, leaf nitrogen concentrations were decreased under CO₂ enrichment at both nitrogen levels. For the low-nitrogen treatment, this resulted in lower photosynthetic rates measured at 650 l/l for the CO₂-enriched plants, compared to photosynthetic rates measured at 350 l/l for the non-enriched plants. At higher nitrogen availability, photosynthetic rates of plants grown and measured at 650 l/l were greater than photosynthetic rates of the non-enriched plants measured at 350 l/l. Water use efficiency, however, was increased in enriched plants at both nitrogen levels. CO₂ enrichment stimulated vegetative growth at both high and low nitrogen during most of the vegetative growth phase but, at the end of the experiment, total biomass of the high and low CO₂ treatments did not differ for plants grown at low nitrogen availability. While not statistically significant, CO₂ tended to stimulate seed production at high nitrogen and to decrease it at low nitrogen.     

Experimental approaches to guarantee minimal risk of potential virus in purified monoclonal antibodies

Regarding biological products, increasing awareness of potential side effects have placed great importance not only at protein purity regarding other proteins but on the removal of biologicals such as DNA and especially virus the importance of which may not be known. Monoclonal antibodies (Mab) have come to be an important class of molecules obtained from hybridoma cells, i.e., nonrecombinant cells in culture. It has been noted during the last years, that with rare exceptions hybridoma cell lines contain retrovirus like particles. The infectious nature of the EM-visible particles has been tested for, however, in most cases not been substantiated. In order to bring these valuable biological reagents, Mab's, to good use in man for imaging or therapy, the remaining concern about a potential retroviral infection has to be reduced to an acceptable minimum. We describe experimental approaches for the validation of chromatographic and ultrafiltration steps used in the production of monoclonal antibodies to remove and inactivate murine retrovirus. Present day biotechnological manufacturing processes have been devised incorporating a number of strategic preventive measures that have found wide spread acceptance. They permit to answer the question: how can a potentially harmful infection by an unknown virus be excluded. Knowledge of the efficacy of purification steps to clear infectious model virus is fundamental to devise biotechnological manufacturing processes yielding a purified antibody for use in man.     

Subgroups in theHordeum patagonicum complex (Poaceae)

Seeds of theHordeum patagonicum complex were collected from the field and grown in the greenhouse. The aim was to take a sample of members of the complex, and on the basis of the phenotypic similarities in some morphological and physiological characters, determine whether distinct groups exist. When cluster analyses, to generate hypotheses, and orthodox statistical procedures, for hypotheses obtained a priori, were applied to the reproductive morphology, germination and flowering patterns, onlyH. patagonicum subsp.magellanicum, out of the five recognized taxa, could be distinguished consistently. The remaining four taxa, which overlapped considerably, could be re-formed into three groups whose centroids were different but whose ranges of variation were not distinct from each other. We conclude that the highly cross-compatible members of theH. patagonicum complex, first defined as species and later redefined as subspecies are probably no more than biotypes.