Seasonal carbon isotope discrimination in a grassland community

Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.     

Effect of salinity on growth of four strains of Rhizobium and their infectivity and effectiveness on two species of Acacia

Two Rhizobium strains (WU1001 and WU1008) were isolated from nodules of Acacia redolens growing in saline areas of south-west Australia, and two strains selected from the University of Western Australia's culture collection (WU429 isolated from A. saligna and WU433 from A. cyclops). The growth of each in buffered, yeast extract mannitol broth culture was largely unaffected by salt up to 300 mM NaCl. A slight increase in lag time occurred at concentrations of 120 mM NaCl and above, but cell number at the static phase was not affected. Each of the four Rhizobium strains tested accumulated Na⁺ but showed decreasing levels of sugar with increasing salt in the external medium. Amino acid levels also increased, in some cases by more than tenfold. However, the relative proportion of each remained fairly constant in the bacteria, irrespective of salt treatment. Only trace quantities of proline were detected and there was no increase in this amino acid with salt. Acidic amino acids (glutamate and aspartate) remained as a constant proportion.Rhizobium strains WU429, WU1001 and WU1008 produced effective nodules on both A. cyclops and A. redolens grown in sand with up to 80 mM NaCl (added in nutrient solutions free of nitrogen). Strain WU433 was highly infective on both Acacia species tested at low salt concentrations (2–40 mM NaCl), but infection was sensitive to salt levels at 120 mM NaCl and above. Nodules formed with strain WU433 were, however, ineffective on both A. redolens and on A. cyclops and showed nil or negligible rates of acetylene reduction at all salt concentrations. Strains WU429, WU1001 and WU1008 in combination with a highly salt-tolerant provenance of A. redolens formed symbioses which did not vary significantly in nodule number and mass, specific nodule activity or total N content irrespective of salt level up to 160 mM NaCl. On a more salt sensitive provenance of A. redolens and on A. cyclops the infectivity and effectivity of the Rhizobium strains tested usually decreased as the external salt concentration increased. These data are interpreted to indicate that tolerance of the legume host was the most important factor determining the success of compatible Rhizobium strains in forming effective symbioses under conditions of high soil salinity.     

Analysis of X-chromosome inactivation and presumptive expression of the Wiskott-Aldrich syndrome (WAS) gene in hematopoietic cell lineages of a thrombocytopenic carrier female of WAS

Summary We report on a thrombocytopenic female belonging to a pedigree with the Wiskott-Aldrich syndrome (WAS). Restriction fragment length polymorphism (RFLP) analysis with probe M27, closely linked to the WAS gene, demonstrated that she is a carrier of WAS. Both small-sized and normal-sized platelets were present, suggesting that, unlike the vast majority of WAS carriers, she does not manifest nonrandom X-chromosome inactivation in the thrombopoietic cell lineage. Study of X-chromosome inactivation by means of RFLP and methylation analysis demonstrated that the pattern of X-chromosome inactivation was nonrandom in T lymphocytes, but random in granulocytes. While this is the first complete report on the occurrence of thrombocytopenia in a carrier female of WAS as the result of atypical lyonization, it also suggests that expression of the WAS gene occurs at (or extends up to) a later stage than the multipotent stem cell along the hematopoietic differentiation pathway.     

Walleye, Stizostedion vitreum, and northern pike, Esox lucius, populations in three Alberta lakes

Results are presented from a survey of walleye and northern pike in Ethel, Marie and Wolf Lakes, Alberta conducted May-September, 1983. Three types of experimental gill net were fished, mainly inshore. Northern pike were abundant in all three lakes but white sucker and yellow perch also were common. Walleye were caught in largest numbers in Wolf Lake. Age and growth of both walleye and northern pike were determined from examination of the opercular bones. The walleye in the three lakes were represented by a few strong year classes but there was no synchronism between the lakes. The strong 1975 year class in Ethel and Wolf Lakes may have been correlated with high spring precipitation and heavy run-off. Although there were dominant year classes in the northern pike populations (especially the 1979 year class) the variability was not so marked as in the walleye. There were no significant differences between length-at-age for year classes of walleye in Ethel and Marie or northern pike in all three lakes. In Wolf Lake the 1978 and 1979 year classes grew faster than in previous years. Walleye and northern pike growth was well described by the von Bertalanffy growth model. Females of both species grew to a greater ultimate length and had a longer lifespan than the males. Fecundity data are presented for walleye from Wolf Lake (log₁₀ absolute fecundity = 0.856 + 2.441 log₁₀ length) and northern pike from Marie Lake (log₁₀ absolute fecundity =?2.671+4.052 log₁₀ length). The stomach contents of both species were examined during May and June. The majority of walleye had empty stomachs. Walleye and northern pike in Ethel and Wolf Lakes fed on a variety of fish and invertebrate species but both fed mainly on fish (in particular whitefish) in Marie Lake. The similarity of diet suggests competition for prey species. A walleye yield to commercial fishermen of c. 0.69 kg ha^?1 year^?1 in Wolf Lake has made up 8% of the total catch. Since 1970/71 when mesh size of nets was increased, the yield has been reduced to c. 0.30 kg ha^?1 year^?1. Anglers remove an additional c. 0.48 kg ha^?1 year^?1 walleye from Wolf Lake. Northern pike yields to commercial fishermen have been c. 2.00 kg ha^?1 year^?1 in Wolf Lake. Ethel and Marie Lakes have yielded only poor catches of walleye and northern pike. A yield model was used to illustrate that faster-growing northern pike have higher potential yields than walleye. Walleye produce higher yields in Wolf Lake than in Marie Lake, the reverse being true for northern pike. It is suggested that northern pike could be cropped at a higher rate in Marie and Wolf Lakes with a possible improvement in walleye stocks.     

Endogenous stimulant of prostaglandin endoperoxide synthase activity in human amniotic fluid

In this study we describe the discovery and characterization of a substance in human amniotic fluid that stimulates prostaglandin biosynthesis by a microsome-enriched preparation of bovine seminal vesicles. The stimulatory activity is not retained substantially upon anisotropic ultrafiltration through a filter with a molecular weight exclusion limit of 500. Stimulation of prostaglandin biosynthesis by this substance is time- and concentration-dependent; maximal stimulation of approx. 200% being observed within 20 min of commencing incubation with 1 ml-equivalent of stimulant fraction. Stimulatory activity is demonstrable both in the presence of reduced glutathione (1.3 mM) and L-tryptophan (20 mM), either separately or combined, and in the presence of exogenous arachidonic acid (5-120 microM). In the absence of added cofactors, the stimulatory substance increases the rates of biosynthesis of prostaglandin E2 and prostaglandin F2 alpha to equal extents. The amount of stimulatory substance added to incubations is correlated positively with increased oxygen consumption during incubations. The stimulatory substance is stable to heating at 100 degrees C for 10 min but is inactivated substantially (to less than 20% of original activity) by treatment with pronase. It is concluded that human amniotic fluid contains a substance of relatively low molecular weight, which is proteinaceous in character, that stimulates prostaglandin endoperoxide synthase activity.     

One-carbon metabolism in lectin-activated human lymphocytes

Serine is an essential amino acid for the lectin-mediated transformation of human peripheral blood lymphocytes due to the inability of this cell to synthesize sufficient quantities via either the phosphorylated pathway or by reversal of the serine hydroxymethyltransferase reaction to meet the metabolic demands. The level of intracellular serine is tightly regulated, and the culture medium concentration for optimum cellular transformation falls within a relatively narrow range. The three-carbon atom of serine is the major source of one-carbon units required for purine and pyrimidine nucleotide biosynthesis, but the key effect of both serine deprivation and of high medium serine levels would appear to be on protein synthesis. Although an alternative source of one-carbon units, as provided by high levels of formate in the culture medium, can partially reverse the effects of serine deprivation, the only other demonstrable source of one-carbon units, tryptophan, requires serine for its incorporation and subsequent metabolism. Methionine is also essential for lymphocyte transformation and is involved in the synthesis of a small amount of phosphatidylcholine, although most of this phospholipid is provided by choline and lysophosphatidylcholine from the serum-supplemented culture medium.     

Alpha 1-antitrypsin and serum albumin mRNA accumulation in normal, acute phase and ZZ human liver

Alpha 1-Antitrypsin and albumin mRNA levels of 4 human livers were assessed using a newly sequenced cDNA clone of the carboxyterminal third of alpha 1-antitrypsin and a previously cloned albumin cDNA sequence. The relative concentration of alpha 1-antitrypsin mRNA was the same in poly(A)-containing RNA isolated from acute phase (MM) and alpha1-antitrypsin deficient (ZZ) individuals. In the acute phase liver relative to the normal (MM) liver, total RNA extracts showed a marked decrease in albumin mRNA concentration but no increase in alpha 1-antitrypsin mRNA. The ZZ liver showed decreased total and poly(A)-containing RNA content but the same proportion of alpha 1-antitrypsin to albumin mRNA as in the normal (MM) liver. This supports other evidence that ZZ alpha 1-antitrypsin deficiency is due to a defect in polypeptide processing (secretion) rather than a deficiency in mRNA accumulation.