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Drought is the single most important factor limiting soya bean ( Glycine max L. Merr.) yields in the field. The following study was therefore undertaken to identify phenotypic markers for enhanced drought tolerance in nodulated soya beans. Leaf and nodule parameters were compared in three genotypes: Prima 2000, glyphosate-resistant A5409RG and Jackson, which had similar shoot biomass and photosynthesis rates at the third trifoliate leaf stage under water-replete conditions. When water was withheld at the third trifoliate leaf stage, photosynthesis, nodule numbers, nodule biomass and symbiotic nitrogen fixation (SNF) were greatly decreased. Significant cultivar-drought interactions were observed with respect to photosynthesis, which also showed a strong positive correlation with nodule SNF, particularly under drought conditions. Prima leaves had high water-use efficiencies, and they also maintained high photosynthetic electron transport efficiencies under long-term drought. Moreover, Prima had the highest shoot biomass under both water-replete and drought conditions. A-5409RG was the most drought-sensitive genotype showing early closure of stomata and rapid inhibition of photosynthesis in response to drought. In addition to classifying the genotypes in relation to drought tolerance, the results demonstrate that the ability to sustain shoot biomass under nitrogen limitation is an important parameter, which can be easily applied in germplasm screening for drought tolerance in soya bean. [ABSTRACT FROM AUTHOR]

Explores the practice of organ retention following pediatric and perinatal autopsy. Need for hospitals and doctors to develop a honest and accurate process for dealing with families who require information about autopsies.

The aim of this work was to examine whether carbohydrates are involved in signalling N deficiency through source:sink imbalance. Photosynthetic metabolism in tobacco was studied over 8 d during the withdrawal of N from previously N-sufficient plants in which the source:sink ratio was manipulated by shading leaves on some of the plants. In N-sufficient plants over this timescale, there was a small decline in photosynthetic rate, Rubisco protein and amino acid content, with a larger decrease in carbohydrate content. Withdrawal of N from the growing medium induced a large decrease in the rate of photosynthesis (35% reduction after 8 d under the growing conditions, with a reduction also apparent at high and low measuring CO2), which was caused by a large decrease in the amount of Rubisco protein (62% after 8 d) and Rubisco activity. Higher amounts of hexoses preceded the loss of photosynthetic activity and sucrose and starch accumulation. Reduction of the source:sink ratio by shading prevented the loss of photosynthetic activity and the increase in hexoses and other carbohydrates. These data indicate that the reduction of photosynthesis that accompanies N deficiency in intact plants has the characteristics of sugar repression of photosynthesis observed in model systems, but that the accumulation of hexose prior to the decline in photosynthesis is small. The possibility that sugar repression of photosynthesis under physiological conditions depends more crucially on the C:N status of leaves than the carbohydrate status alone is discussed. [ABSTRACT FROM AUTHOR]

Winter wheat (Triticum aestivum L., cv. Mercia) was grown at two different atmospheric CO2 concentrations (350 and 700 μmol-1), two temperatures [ambient temperature (i.e. tracking the open air) and ambient +4 °C] and two rates of nitrogen supply (equivalent to 489 kg ha-1 and 87kg ha-1). Leaves grown at 700 μmol mol-1 CO2 had slightly greater photosynthetic capacity (10% mean increase over the experiment) than those grown at ambient CO2 concentration, but there were no differences in carboxylation efficiency or apparent quantum yield. The amounts of chlorophyll, soluble protein and ribulose- 1,5-bisphosphate carboxylase/oxygenase (Rubisco) per unit leaf area did not change with long-term exposure to elevated CO2 concentration. Thus winter wheat, grown under simulated field conditions, for which total biomass was large compared to normal field production, did not experience loss of components of the photosynthetic system or loss of photosynthetic competence with elevated CO2 concentration. However, nitrogen supply and temperature had large effects on photosynthetic characteristics but did not interact with elevated CO2 concentration. Nitrogen deficiency resulted in decreases in the contents of protein, including Rubisco, and chlorophyll, and decreased photosynthetic capacity and carboxylation efficiency. An increase in temperature also reduced these components and shortened the effective life of the leaves, reducing the duration of high photosynthetic capacity. [ABSTRACT FROM AUTHOR]

The requirements for the experimental study of the effects of global climate change conditions on plants are outlined. A semi-controlled plant growth facility is described which allows the study of elevated CO2 and temperature, and their interaction on the growth of plants under radiation and temperature conditions similar to the field. During an experiment on winter wheat (cv. Mercia), which ran from December 1990 through to August 1991, the facility maintained mean daytime CO2 concentrations of 363 and 692 cm³ m-3 for targets of 350 and 700 cm³ m-3 respectively. Temperatures were set to follow outside ambient or outside ambient +4°C, and hourly means were within 0.5°C of the target for 92% of the time for target temperatures greater than 6°C. Total photosynthetically active radiation incident on the crop (solar radiation supplemented by artifical light with natural photoperiod) was 2% greater than the total measured outside over the same period. [ABSTRACT FROM AUTHOR]

Winter wheat (Triticum aestivum L., cv. Mercia) was grown in chambers under light and temperature conditions similar to the UK field environment for the 1990/1991 growing season at two levels each of atmospheric CO2 concentration (seasonal means: 361 and 692 μmol mol-1), temperature (tracking ambient and ambient +4 °C) and nitrogen application (equivalent to 87 and 489 kg ha-1 total N applied). Total dry matter productivity through the season, the maximum number of shoots and final ear number were stimulated by CO2 enrichment at both levels of the temperature and N treatments. At high N, there was a CO2-induced stimulation of grain yield (+15%) similar to that for total crop dry mass (+12%), and there was no significant interaction with temperature. This contrasts with other studies, where positive interactions between the effects of increases in temperature and CO2 have been found. Temperature had a direct, negative effect on yield at both levels of the N and CO2 treatments. This could be explained by the temperature-dependent shortening of the phenological stages, and therefore, the time available for accumulating resources for grain formation. At high N, there was also a reduction in grain set at ambient +4 °C temperature, but the overall negative effect of warmer temperature was greater on the number of grains (-37%) than on yield (-18%), due to a compensating increase in average grain mass. At Low N, despite increasing total crop dry mass and the number of ears, elevated CO2 did not increase grain yield and caused a significant decrease under ambient temperature conditions. This can be explained in terms of a stimulation of early vegetative growth by CO2 enrichment leading to a reduction in the amount of N available later for the formation and filling of grain. [ABSTRACT FROM AUTHOR]

Abstract The aim of this work was to establish the quantitative impact of photorespiration on leaf amino acid contents. Attached leaves of wheat and potato were incubated for 30–40 min under defined conditions in which net CO2 uptake (A ) was manipulated by irradiance, ambient CO2 or ambient O2 . The incubated portion of the leaf was sampled by a rapid-quench method and photorespiratory flux (v o ) was modelled from the measured rate of net CO2 uptake. In both wheat and potato, the ratio between glycine and serine showed a strong positive correlation with v o . Aspartate and alanine correlated negatively with v o but glutamate and glutamine showed less clear relationships. In potato, glutamate and glutamine did not correlate clearly with either A or v o . In wheat, glutamine showed a general increase with A but no relationship with v o , whereas 2-oxoglutarate contents correlated positively with v o and negatively with A . As a result, glutamine : glutamate and glutamine : 2-oxoglutarate increased with net CO2 uptake in wheat, observations that are attributed primarily to imperfect and variable coupling between the supply of NH3 in primary nitrogen assimilation and the associated delivery of 2-oxoglutarate to the chloroplast. A simple theoretical analysis is used to illustrate the potentially marked impact of primary nitrogen assimilation on leaf glutamine, even against a background of high rates of photorespiratory ammonia recycling. [ABSTRACT FROM AUTHOR]

Equilibrium partitioning (EqP) theory, which has been used to develop sediment quality criteria, predicts that the effects of organic compounds in sediments can be assessed by comparison of organic carbon-normalized sediment concentrations and estimated pore-water concentrations to effects determined in water-only exposures. A complementary approach, the critical body residue (CBR) theory, examines actual bodyburdens in relation to toxic effects. Critical body residue theory predicts that the narcotic effects of nonpolar compounds should be essentially constant for similar organisms, and narcosis should be observed at body burdens of 2 to 8 5 mol/g tissue. This study compares these two approaches for predicting toxicity of the polycyclic aromatic hydrocarbon (PAH) fluoranthene. The freshwater amphipods Hyalella azteca and Diporeia spp, were exposed for up to 30 d to sediment spiked with radiolabeled fluoranthene at concentrations of 0.1 (trace) to 3,940 nmol/g dry weight (= 346 5 mol/g organic carbon). Mean survival of Diporeia was generally high (>70%) and not significantly different from that of control animals. This result agrees with EqP predictions, because little mortality was observed for Diporeia in 10-d water-only exposures to fluoranthene in previous studies. After 10-d exposures, mortality of H. azteca was not significantly different from that of controls, even though measured interstitial water concentrations exceeded the previously determined 10-d water-only median lethal concentration (LC50). Equilibrium partitioning overpredicted fluoranthene sediment toxicity in this species. More mortality was observed for H. azteca at later time points, and a 16-d LC50 of 3,550 nmol/g dry weight sediment (291 5 mol/g organic carbon) was determined. A body burden of 1.10 5 mol fluoranthene-equivalents/g wet weight in H. azteca was associated with 50% mortality after 16-d exposures. Body burdens ashigh as 5.9 5 mol/g wet weight resulted in little mortality in Diporei [ABSTRACT FROM AUTHOR]

Two 10-d water-only toxicity tests with radiolabeled fluoranthene were conducted with two species of freshwater amphipods, Hyalelia azteca and Diporeia sp. For H. azteca, 10-d median lethal concentrations were 564 nmol/L and 481 nmol/L. Tentative median lethal doses, determined from the regressions of body burden of remaining live H. azteca versus survival, were 5.6 and 3.6 mmol fluoranthene/kg wet weight tissue. Diporeia appeared to be less sensitive, because survival in Diporeia wasgreater than 84% after 10-d exposures. Elimination rates determined for Diporeia, ranging from 0.0011 to 0.0042/h (half-lives of 7--26 d), were much slower than rates determined for H. azteca of 0.128to 0.188/h (half-lives of 4--6 h). Faster elimination in H. azteca may be related to its greater ability to metabolize fluoranthene. For H. azteca, an average of 17% of its body burden was present as metabolites after 24 h of exposure to radiolabeled fluoranthene, as compared to 5% for Diporeia. For Diporeia, exposure to various water concentrations of fluoranthene for various lengths of time resulted in declines in the conditional uptake clearance rates (ml water cleared/g wetweight tissue/h). A similar, although less dramatic trend was observed for conditional uptake clearance rates in H. azteca. [ABSTRACT FROM AUTHOR]

Current protocols for conducting freshwater sediment bioaccumulationtests recommend that food not be added to exposures, whereas toxicity tests require food addition. To determine effects of adding food onexposure, 30-d sediment exposures were conducted with Hyalella azteca to sediment dosed with four fluoranthene concentrations (trace level to 897 nmol/g dry weight). Accumulation was significantly greater in fed versus nonfed animals at all dose levels after 96 h of exposureand continued to be greater after 30 d in the low dose levels. At sediment concentrations above 478 nmol/g dry weight, survival of unfed animals dropped to 34% after 30 d. After 30 d of exposure, growth andreproduction were observed in fed animals exposed to sediment concentrations 20 to 90 times the expected median lethal concentration (LC50) values for fluoranthene in sediment, according to 10-d studies reported in the literature using sediment with comparable organic carbonconcentrations. Samples of sediment in exposure beakers taken from the sediment-water interface (flocculent layer) and 1 to 2 cm below the interface had large differences in fluoranthene and organic carbon concentrations. The concentration of fluoranthene was 2 to 10 times greater in the flocculent layer, the area inhabited by H. azteca, compared to the deeper sediment. These data raise questions concerning the interpretation of standard toxicity and bioaccumulation tests when food is routinely added. [ABSTRACT FROM AUTHOR]

Two freshwater amphipods, Hyatella azteca and Diporeia sp., were exposed to sediment spiked with radiolabeled fluoranthene at nominal concentrations of 0.1 (trace) to 1,270 nmol fluoranthene/g dry weight. In two experiments, uptake kinetics and mortality were determined over30-d exposures. Concentrations of fluoranthene in sediment and pore water were also measured. Mean survival of H. azteca was generally high, greater than 90% after 10 or 16 d, and greater than 74% after 30 d. Mean survival was lower for Diporeia, 14% after a 30-d exposure tothe highest sediment concentration in experiment 1, and 53% in experiment 2. Tissue concentrations in Diporeia were as high as 2 to 4 mu mol/g wet weight, a body burden that could be expected to result in death by narcosis. Hyalella azteca did not typically accumulate more than 1 mu mol/g wet weight, which is consistent with the lower observed mortality. Apparent steady-state biota-sediment accumulation factors (BSAFs, lipid- and organic-carbon-normalized) for sediment concentrations other than trace level tended to be higher for Diporeia (0.345--0.818) than for H. azteca (0.161--0.612). The BSAFs for trace levels tended to be lower for both species (0.045--0.436) in comparison tohigher sediment concentrations. For both organisms, the internal concentration based on body residue was a more reliable indicator of toxicity than were equilibrium partitioning predictions. [ABSTRACT FROM AUTHOR]