Showing papers by "Swedish University of Agricultural Sciences published in 1982"

Fluorescein diacetate hydrolysis as a measure of total microbial activity in soil and litter.

Abstract: Spectrophotometric determination of the hydrolysis of fluorescein diacetate (FDA) was shown to be a simple, sensitive, and rapid method for determining microbial activity in soil and litter. FDA hydrolysis was studied in soil and straw incubated for up to 3 h. Hydrolysis was found to increase linearly with soil addition. FDA hydrolysis by pure cultures of Fusarium culmorum increased linearly with mycelium addition both in shake cultures and after inoculation into sterile soil. FDA hydrolysis by Pseudomonas denitrificans increased linearly with biomass addition. The FDA hydrolytic activities in soil samples from different layers of an agricultural soil were correlated with respiration. Acetone was found to be suitable for terminating the reaction.

Mechanism of the anticoagulant action of heparin

Abstract: The anticoagulant effect of heparin, a sulfated glycosaminoglycan produced by mast cells, requires the participation of the plasma protease inhibitor antithrombin, also called heparin cofactor. Antithrombin inhibits coagulation proteases by forming equimolar, stable complexes with the enzymes. The formation of these complexes involves the attack by the enzyme of a specific Arg-Ser bond in the carboxy-terminal region of the inhibitor. The complexes so formed are not dissociated by denaturing solvents, which indicates that a covalent bond may contribute to their stability. This bond may be an acyl bond between the active-site serine of the enzyme and the arginine of the cleaved reactive bond of the inhibitor. However, the native complexes dissociate slowly at near-neutral pH into free enzyme and a modified inhibitor, cleaved at the reactive bond. So, antithrombin apparently functions as a pseudo-substrate that traps the enzyme in a kinetically stable complex.

Relative addition rate and external concentration; Driving variables used in plant nutrition research

Abstract: An increasing literature accounting for various types of experiments indicates that far lower external nutrient concentrations are required by plants than is usually thought to be the case. It is concluded that the ion uptake capacity of the roots, as described by the carrier concept, is high compared to that required for maintenance of the internal concentration. Serious errors in experimental conclusions are associated with insufficient and constant nutrient addition rates. The main errors are caused by non-steady states of the plants both with regard to the internal nutrient concentrations and the relative growth rate. A dynamic concept has been proposed for direct use as the treatment variable within the range of sub-optimum nutrition. The nutritional factor is expressed as a flow, the relative nutrient addition rate in laboratory studies and the nutrient flux density in the field. The experimental use of the relative addition rate has led to steady-state nutrient status and relative growth rate and the interpretation of plant responses which differ fundamentally from accepted views. Thus, for instance, deficiency symptoms disappear, as in natural conditions, when the internal nitrogen concentration is stable, independent of level. The nutrition/growth relationships are very different from those observed when external concentration is varied. The regression line of relative growth rate on relative addition rate passes near to the origin at an angle close to 45 to the axes, which implies that the obtained relative growth rate approximates closely the treatment variable. A striking example of observed differences is the positive effect on nitrogen fixation exerted by high relative nitrogen addition rates compared to the well-known negative effect of increasing external nitrogen concentration. The application of fertilizer on the basis of the nutrient flux density concept provides the possibility of supplying fertilizers corresponding to the consumption potential of the vegetation and to the natural flux density resulting from mineralization in the soil. Nitrogen utilization is high under such conditions and the resulting feedback of nutrition on the mineralization rate suggests that there will be a long-term increase in fertility.

The polyserial correlation coefficient.

Abstract: The polyserial and point polyserial correlations are discussed as generalizations of the biserial and point biserial correlations. The relationship between the polyserial and point polyserial correlation is derived. The maximum likelihood estimator of the polyserial correlation is compared with a two-step estimator and with a computationally convenient ad hoc estimator. All three estimators perform reasonably well in a Monte Carlo simulation. Some practical applications of the polyserial correlation are described.

Nitrification in forested ecosystems

Abstract: Nitrification, the microbial oxidation of NH $^+\_4$ -N, plays a key role in the cycling of N in forested and other terrestrial ecosystems. Solution losses of nitrate and gaseous losses of N $\_2$ and nitrous oxides are important vectors of N loss from many forested systems and are directly or indirectly controlled by the activity of the nitrifiers. These losses can also have important consequences for downstream ecosystems, groundwater quality, and atmospheric concentrations of ozone. Relative nitrification (the proportion of the total mineral N that is nitrate at the end of an incubation period) provides an independent means of evaluating the general importance of site factors thought to regulate nitrification in situ. Regression of relative nitrification against soil pH, C:N, and percentage N, with the use of data from previously published studies, suggest that although these factor may be important regulators of nitrification in particular sites, they are not good predictors of nitrification across a wide range of sites. Reasons for their low predictive ability may include limitations of current measurement techniques or the capacity of nitrifiers to adapt to relatively extreme conditions.

Inhibitory effect of low partial pressures of acetylene on nitrification

Abstract: The inhibiting effect of C 2 H 2 on nitrification was investigated in two agricultural soils. Nitrification was totally inhibited at 10 Pa partial pressure of C 2 H 2 which is lower than previously reported for soils. There were no differences in rates of nitrate production between flasks without C 2 H 2 and flasks with C 2 H 2 at 0.01 Pa, while there was an effect on nitrification at 0.1 PaC 2 H 2 . At 0.1 Pa no inhibition was noted during the first 3 days; after this period nitrification was partially inhibited. The inhibiting effect did not cease until 7 days after removal of C 2 H 2 . The sensitivity of nitrification to low concentrations of C 2 H 2 should be noted when denitrification rates are determined by the use of the acetylene inhibition method (usually C 2 H 2 at 10kPa).

Gas exchange in a 20-year-old stand of Scots pine

Abstract: The rates of net photosynthesis and transpiration of one-year-old shoots were measured in situ in five different positions within the crown of a young Scots pine (Pinus sylvestris L.). Measurements were carried out on south- and north-facing shoots on the third and sixth whorls, respectively, and on an east-facing shoot on the ninth whorl. In another investigation the rates of gas exchange of one-year-old shoots on the third whorl of eight different trees were studied. The measurements were made during June and July, 1977, under non-limiting conditions of soil water. The daily rates of net photosynthesis in whorls three and six followed the light conditions closely, with higher rates for the south side of each whorl and higher for whorl three than six. On whorl nine the shoot had a higher light compensation point and a low rate of photosynthesis at light saturation compared to the other shoot positions. The quantum yield for the shoot on the lowest whorl, as estimated from the linear part of the light response curve, was 50% lower than for shoots on whorl three and six. The variation in transpiration rates was pronounced within the crown as an effect of differences in the absolute value and diurnal course of stomatal conductance. The variation in net photosynthesis was small between different trees while the variation in transpiration was much higher. Thus the variation in water use efficiency was great. It is concluded that it is possible to extrapolate measurements of net photosynthesis from individual trees up to a stand level without introducing large errors in the estimate. More caution must be paid before extrapolating tree transpiration up to stand transpiration. However, before an extrapolation of gas exchange is made from tree to stand level the variation in net photosynthesis and transpiration rate within the crown must be known.

Microbiological regulation of the biogeochemical nitrogen cycle

Abstract: Most nitrogen transformations in soil are carried out by micro-organisms. An understanding of the microbiological processes is thus necessary in order for us to devise management practices in agricultural ecosystems, which will optimize plant root uptake of nitrogen and minimize nitrogen losses from the systems. Some aspects of the individual microbiological processes in the nitrogen cycle are discussed and their importance for an efficient management of agroecosystems.

Evidence for similar conformational changes in α2-macroglobulin on reaction with primary amines or proteolytic enzymes

Abstract: Reactions of alpha(2)-macroglobulin (alpha(2)M) with primary amines (ammonium chloride, methylammonium chloride and ethylammonium chloride) or proteolytic enzymes (trypsin, chymotrypsin and thrombin) resulted in changes of the absorption, fluorescence and circular-dichroism spectra and of the sedimentation coefficient of the inhibitor. All physico-chemical changes caused by the inactivation of alpha(2)M by the amines were identical with, or highly similar to, those induced by the formation of the enzyme-inhibitor complexes. This suggests that similar conformational changes of the inhibitor occur in the two types of reactions. The frictional ratio, calculated from the increase in sedimentation coefficient, decreased from 1.67 for untreated alpha(2)M to 1.57 for the amine- or proteinase-treated inhibitor. This change is due to a decrease in either asymmetry or hydration of the protein, resulting in a slightly smaller hydrodynamic volume. The circular-dichroism analyses indicated that the reaction of alpha(2)M with either amines or proteinases is accompanied by a loss of the small amount (about 5%) of alpha-helix of the untreated protein. The changes of u.v. absorption and fluorescence suggested that about one out of the eight to ten tryptophan residues of each alpha(2)M subunit is buried as a result of the conformational change. All spectroscopic and hydrodynamic changes that were observed are compatible with a spatial rearrangement of the subunits of alpha(2)M, as implicated by the ;trap' hypothesis for the mechanism of inhibition of proteinases. However, a conformational change involving a decrease in the hydrodynamic volume of each subunit cannot be excluded.

Mycorrhizal associations in some woodland and forest trees and shrubs in tanzania

Abstract: SUMMARY The mycorrhizal associations in 47 indigenous Tanzanian trees and shrubs, mainly from less humid areas, were studied. Forty species were found to be endomycorrhizal. One, Uapaca kirkiana Mull. Arg. (Euphorbiaceae) was ectendomycorrhizal while six, four Brachystegia spp., Julbernardia globiflora (Benth.) Troup. (Caesalpiniaceae) and Monotes elegans Gilg. (Diptero-carpaceae), were ectomycorrhizal. The results demonstrated a dominance of endomycorrhizal species, which is typical for the tropics and is further reinforced by taxonomic considerations. However, in the Miombo (Brachystegia–Julbernardia) woodlands, a major ecosystem in East and South Central Africa, ectomycorrhizal trees predominate in volume. In three other ecosystems studied – a Combretum woodland, a groundwater forest and a semi-evergreen forest–ectomycorrhizal species were absent or almost absent. Nodulated leguminous species appeared to be more common in the fire-induced woodlands than in the closed forests.

Cytokinins as inhibitors of root growth

Abstract: The elongation of roots of wheat (Triticum aestivum L. cv. Diamant II), flax (Linum usitatissimum L. cv. Concurrent) and cucumber (Cucumis sativus L. cv. Favor) seedlings in the dark was strongly inhibited by various native and synthetic cytokinins (kinetin, benzyladenine, isopentenyladenine, zeatin and their corresponding 9-ribosides). An inhibition of 50% was obtained for wheat roots with 3 · 10−9M zeatin and for flax roots with 6 · 10−9M isopentenyladenine. The ribosides were in all cases less inhibitory. The inhibition was reversed by various types of ‘antiauxins’ and ‘antiethylenes’ (such as structural auxin analogues, uncouplers, specific inhibitors of ethylene synthesis, free radical scavengers, inhibitors of ethylene action). These substances as a rule counteract also inhibitions caused by auxins. Auxins and cytokinins stimulate ethylene production synergistically, and the similar inhibitory effects of these two types of hormone can be understood if it is assumed that their effect is at least partly mediated through ethylene. The cytokinins must be considered as possible natural inhibitors and regulators of root growth.

Immune functions of human synovial cells. phenotypic and t cell regulatory properties of macrophage-like cells that express hla–dr

Abstract: Normal and rheumatoid synovial cells have been analyzed in frozen sections and in suspension. HLA-DR-expressing, macrophage-like cells are demonstrated in normal synovial intima and in rheumatoid tissue. Suspended normal synoviocytes equaled peripheral blood non-T lymphocytes as stimulators of mixed lymphocyte reactions, whereas adherent rheumatoid synovial cells were extremely efficient as such stimulators and in presenting soluble antigens to autologous T lymphocytes. This HLA-DR-dependent T lymphocyte regulation might provide a cellular basis for the HLA-D haplotype-arthritis associations.

Adaptive versus incidental explanations for the occurrence of protandry in a butterfly, leptidea sinapis l.

Abstract: In many butterflies males emerge before females (Petersen, 1892; Demoll, 1908; Berge and Rebel, 1910; Ford, 1945; Petersen, 1947; Forster, 1954; Newman, 1968). This phenomenon, here referred to as protandry, is also known from other insects (Petersen, 1892; Demoll, 1908; Petersen, 1947). At least two general classes of hypotheses can be invoked to explain the occurrence of protandry. First, the time difference per se in eclosion times may be the result of selective pressures on males and females to emerge at different times in relation to each other. This class of explanations is here called "adaptive." Thus, for example, Wiklund and Fagerstr6m (1977) argue that sexual selection between males to maximize the number of matings leads to protandry. It has also been argued that sexual selection between females to minimize the risk of death prior to mating also leads to protandry (Ford,, 1945; Bowden, 1979; Wiklund and Fagerstrom, 1979). If eclosions are similarly distributed among males and females the optimal difference in eclosion time is similar for male and female strategies (Wiklund and Fagerstr6m, unpubl.). Another "adaptive" hypothesis claims that selection for outbreeding can explain the incidence of protandry in butterflies (Petersen, 1892) thus presupposing that males are better suited for dispersal than females. Second, the difference in eclosion times may be a byproduct of selection for other life history traits. For example, in many butterflies males are smaller than females (which may be adaptive per se) and thus as an incidental byproduct of the size difference between the sexes. We call this class of explanations for the occurrence of protandry "incidental." Recently Lewontin (1977, 1978a, 1978b) and Gould and Lewontin (1979) have stressed the importance of seriously considering non-adaptive or incidental explanations for various "traits." The aim of this paper is to report the results of experiments aimed at distinguishing between "adaptive" and "incidental" explanations for the occurrence of protandry in a butterfly, the Wood White Leptidea sinapis L. (Lepidoptera: Pieridae). (We are aware of the fact that the term "adaptive" is in part ambiguous. For example a trait can have a positive adaptive value without having been selected for [cf. Williams, 1966; Futuyma, 1979]. We therefore want to state explicitly that in this paper "adaptive" is used synonymously with "selected for. ") The basis for our attempt to distinguish between these two classes of explanations is the occurrence of two developmental phenotypes in L. sinapis. By using different phenotypes (in this case two generations) of the same species we gain the advantage of comparing organisms with the same physiological constraints or "Bauplan" (cf. Gould and Lewontin, 1979) thus avoiding the problems of comparing different species that are always to some extent trapped in their particular evolutionary pasts (cf. Solbreck, 1978). Pertinent points in the biology of L. sinapis in Sweden follow. The insect overwinters in the pupal stage. In spring males emerge from the pupae a couple of days before females (Wiklund, 1977). Follow-

Structure and physiology of ectomycorrhizae

Abstract: SUMMARY The process of mycorrhiza formation in previously uninfected roots was studied in vitro, using the fungus Piloderma croceum Erikss. & Hjortst, and the Norway spruce, Picea abies (L.) Karst, as model organisms. The process could be divided into the following phases: fungal growth stimulation by root metabolites; formation of a hyphal envelope on the root; intercellular penetration by single hyphae, change in fungal morphology into labyrinthic tissue formation leading to Hartig net formation, and extension of labyrinthic tissue to form a mantle. P. croceum, growing in dead tissue, showed saprophytic growth in vitro, a capacity suppressed in living tissue. The way of fungal penetration appeared to be mechanical. A hypothetical model for host-fungus interactions regulating the mycorrhiza infection process is also discussed.

Studies on Lactation Yield and Individual Test-day Yields of Swedish Dairy Cows

Abstract: (1982) Studies on Lactation Yield and Individual Test-day Yields of Swedish Dairy Cows Acta Agriculturae Scandinavica: Vol 32, No 1, pp 103-114

Effects of heparin oligosaccharides with high affinity for antithrombin III in experimental venous thrombosis.

Abstract: The in vitro and in vivo characteristics of two oligosaccharide heparin fragments have been compared to those of unfractionated mucosal heparin. A decasaccharide fragment had essentially no activity by APTT or calcium thrombin time assays in vitro, but possessed very high specific activity by anti-Factor Xa assays. When injected into rabbits at doses of up to 80 microgram/kg, this fragment was relatively ineffective in impairing stasis thrombosis despite producing high blood levels by anti-Xa assays. A 16-18 monosaccharide fragment had even higher specific activity (almost 2000 iu/mg) by chromogenic substrate anti-Xa assay, with minimal activity by APTT. When injected in vivo, this fragment gave low blood levels by APTT, very high anti-Xa levels, and was more effective in preventing thrombosis than the decasaccharide fragment. However, in comparison with unfractionated heparin, the 16-18 monosaccharide fragment was only partially effective in preventing thrombosis, despite producing much higher blood levels by anti-Xa assays. It is concluded that the high-affinity binding of a heparin fragment to antithrombin III does not by itself impair venous thrombogenesis, and that the anti-Factor Xa activity of heparin is only a partial expression of its therapeutic potential.

Nitrogen fixation by the woody legumeLeucaena leucocephala in Tanzania

Abstract: The nitrogen fixation rate in a 4-year-old stand of the woody legumeLeucaena leucocephala (Lam.) de Wit. was estimated in the field at a rather dry site in Tanzania by use of an acetylene reduction technique. The diurnal mean value during April–May was 35 nmol C2H4 mg−1 (dry weight) nodules h−1, with a variation between 22±8 and 48±12 nmol C2H4 mg−1 (dry weight) nodules h−1 in early morning and at midday, respectively. The nodule biomass was determined by auger sampling to be 51±16 kg (dry weight) ha−1. Most of the nodules were found at the 10–30 cm soil depth level. A rough calculation of the amount of nitrogen fixed annually arrived at 110±30 kg ha−1. The results give strong support for the use ofL. leucocephala for soil enrichment in less humid areas of tropical Africa.

Uptake of SO2 in shoots of Scots pine: field measurements of net flux of sulphur in relation to stomatal conductance

Abstract: UPTAKE OF SO2 IN SHOOTS OF SCOTS PINE - FIELD-MEASUREMENTS OF NET FLUX OF SULFUR IN RELATION TO STOMATAL CONDUCTANCE