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.     

Selective priming of rate and duration of the respiratory burst of neutrophils by 1,2-diacyl and 1-O-alkyl-2-acyl diglycerides. Possible relation to effects on protein kinase C

Both 1,2-diacyl- and 1-O-alkyl-2-acyl-sn-glycerols are released during stimulation of human polymorphonuclear leukocytes (PMNL). 1,2-Diacylglycerols have received intense interest as intracellular "second messengers" due to their ability to activate protein kinase C (Ca2+ phospholipid-dependent enzyme). However, little is known about bioactivities of the alkylacylglycerols. This study compared the ability of 1,2-diacyl- and 1-O-alkyl-2-acylglycerols to modulate the respiratory burst of stimulated PMNL, a response which depends on the activation of an NADPH oxidase to generate bactericidal species of reduced oxygen. Direct stimulation by N-formyl-Met-Leu-Phe caused an abrupt release of H2O2 which ceased within 2.5 min. Preincubation with diacylglycerols (1-oleoyl-2-acetylglycerol,5-30 microM, and 1,2-dioctanoylglycerol,2-5 microM) caused a decrease in lag time, 3-fold increase in initial rate of H2O2 release, and marked prolongation of the response to N-formyl-Met-Leu-Phe (features characteristic of a priming effect). Preincubation with alkylacylglycerols (1-O-delta 9-octadecenyl-2-acetylglycerol, 5-30 microM, and 1-O-octyl-2-octanoylglycerol, 20-50 microM) primed initiation (shortened lag time and increased velocity) but, in contrast to diacylglycerols, did not alter duration of H2O2 release. While low concentrations of diacylglycerols (5-30 microM) primed PMNL, higher concentrations (greater than or equal to 70 microM) stimulated the cells directly. In contrast, higher (70-100 microM) concentrations of alkylacylglycerols did not prime the responses but, in fact, inhibited priming (especially of duration) induced by diacylglycerol. The high concentrations of alkylacylglycerol also inhibited direct stimulation induced by high concentrations of diacylglycerol. Direct stimulation by high concentrations of diacylglycerol probably involves activation of protein kinase C, whereas alkylacylglycerol was found to inhibit activation of protein kinase C by diacylglycerol in vitro. Thus, diacylglycerols are complete priming agonists, altering both rate and duration of the response. In contrast, alkylacylglycerols may have biphasic, concentration-related effects in modulation of functions of PMNL. At low concentrations, they may facilitate initiation of functional events; however, as their concentration increases, they may serve to terminate responses. The distinct priming effects of these diglycerides also reveal that priming can involve at least two distinct events: 1) initiation and 2) prolongation.(ABSTRACT TRUNCATED AT 400 WORDS)     

Activation of MHC-restricted rat T cells by cloned syngeneic thyrocytes

We have previously demonstrated that rat thyrocytes express MHC class II Ag (RT1.B&D) in response to IFN-gamma. To determine whether MHC class II-positive thyrocytes can be recognized by MHC-restricted T cells, we used our clone of rat thyroid cells (1B-6) derived from the Fisher rat thyroid cell line (FRTL-5) and known to express MHC class II Ag in response to recombinant rat IFN-gamma. CD4+ and CD8+ normal syngeneic Fisher rat spleen T cells were selected by flow cytometry and averaged greater than 96% purity. We demonstrated that irradiated MHC class II-positive but not class II-negative 1B-6 thyrocytes stimulated CD4+ T cells in a primary sensitization reaction over 4 days. In contrast, CD8+ T cells had no response in similar experiments. This stimulation of CD4+ T cells was dose dependent for 1B-6 thyrocytes and was abrogated by anti-rat MHC class II mAb (MRC OX-6). Autoreactive (Fisher) and alloreactive (Buffalo) T cell lines and isolated CD4+ T cells derived from these lines, which were developed against Fisher rat spleen cells, similarly recognized MHC class II Ag expressed on 1B-6 cells but had no detectable response to 1B-6 MHC class II-negative thyrocytes or MHC class II-positive human thyroid cells. The CD4+ T cell recognition of 1B-6 cells via MHC class II Ag supports our previous data with autologous human thyroid T cell co-cultures and is indicative of an autospecific role for thyrocytes in the development of autoimmune thyroiditis.     

Evaluation of eight and a half years of neonatal screening for haemoglobinopathies in Birmingham

A pilot neonatal screening programme for haemoglobinopathies linked with screening for phenylketonuria and congenital hypothyroidism was reviewed. During 1978 to December 1986 137 000 neonates were tested. There were improvements in the detection rate and accuracy of diagnosis for homozygotes and mixed heterozygotes, mainly associated with the introduction of citrate agarose gel electrophoresis as a follow up procedure on all specimens showing any abnormality on the initial cellulose acetate electrophoresis.We recommend that the programme is continued on a service basis.     

Glomerular bypass shunts and distribution of glomeruli in the kidney of the lesser spotted dogfish,Scyliorhinus caniculus

Summary Scanning electron microscopy of corroded resin casts of the renal vasculature of Scyliorhinus caniculus has revealed a novel vascular pathway arising from the afferent arteriole and bypassing the glomerulus. This glomerulus bypass shunt occurred in 36% of the glomerular casts examined. The shunt ran to join a peritubular network of capillaries and thereby offers the potential to vary the degree of glomerular perfusion and control the proportion of active glomeruli. In 29% of glomeruli two efferent arterioles drained the capillary knot. Glomeruli were located close to the dorsal margin of the posterior mass of the kidney, and towards the lateral edge of the anterior lobes of the kidney of female dogfish. In male dogfish, glomeruli were evenly distributed through the posterior mass of kidney, while in female dogfish 89% of glomeruli occurred in the posterior mass and 11% of glomeruli were located within the small anterior lobes.     

Genomic potential of erythroid and leukocytic cells of Rana pipiens analyzed by nuclear transfer into diplotene and maturing oocytes

In order to determine whether differentiated somatic cells maintain genetic totipotency, nuclear transplantations from several differentiated somatic cell types into eggs and oocytes were performed previously in Rana pipiens and Xenopus laevis. The formation of postneurula embryos and tadpoles under the direction of the test nuclei demonstrated their genetic multipotency. In addition, Rana erythrocyte nuclei transplanted to oocytes directed more extensive tadpole development than those injected into eggs. We have extended our studies of the genomic potential of differentiated somatic nuclei from the peripheral blood of Rana pipiens. First, we show that the developmental potential of erythrocyte nuclei injected into oocytes at first meiotic metaphase was greater than those injected into diplotene oocytes. Second, we demonstrate that erythroblast and leukocyte nuclei transplanted to oocytes at first meiotic metaphase promoted more advanced tadpole development than those previously injected into Xenopus eggs. Third, erythrocyte nuclei were more successful in promoting advanced tadpole development compared with erythroblast and leukocyte nuclei. The results show that differentiated somatic nuclei transferred to the cytoplasm of oocytes at first meiotic metaphase display enhanced genomic and developmental potential over those transplanted to diplotene oocytes and eggs, at least for the three nuclear cell types tested from the peripheral blood.