Are Swedish forest soils sinks or sources for CO<Subscript>2</Subscript>—model analyses based on forest inventory data

Forests soils should be neither sinks nor sources of carbon in a long-term perspective. From a Swedish perspective the time since the last glaciation has probably not been long enough to reach a steady state, although changes are currently very slow. In a shorter perspective, climatic and management changes over the past 100 years have probably created imbalances between litter input to soils and organic carbon mineralisation. Using extant data on forest inventories, we applied models to analyse possible changes in the carbon stocks of Swedish forest soils. The models use tree stocks to provide estimates of tree litter production, which are fed to models of litter decomposition and from which carbon stocks are calculated. National soil carbon stocks were estimated to have increased by 3 Tg yr⁻¹ or 12–13 g m⁻² yr⁻¹ in the period 1926–2000 and this increase will continue because soil stocks are far from equilibrium with current litter inputs. The figure obtained is likely to be an underestimation because wet sites store more carbon than predicted here and the inhibitory effect of nitrogen deposition on soil carbon mineralisation was neglected. Knowledge about site history prior to the calculation period determines the accuracy of current soil carbon stocks estimates, although changes can be more accurately estimated. This article has previously been published in issue 82/3, under DOI .     

Quantitative changes in secondary metabolites of dark-leaved willow (Salix myrsinifolia) exposed to enhanced ultraviolet-B radiation

This is a study of the impact of increased ultraviolet-B (UV-B) radiation on the secondary chemistry of Salix myrsinifolia (dark-leaved willow). For nearly two decades, the loss of stratospheric ozone above the high latitudes of the Northern Hemisphere has increased UV-B radiation (280–320 nm) over the long-term mean. Willows (Salicaceae) are widely distributed in these northern regions. To determine the effects of increased UV-B radiation on willows, the plantlets of three clones of S. myrsinifolia were grown under ambient (3.6 kJ m⁻² day⁻¹) or enhanced (7.18 kJ m⁻² day⁻¹) UV-B irradiance. After the 2-week indoor experiment, the concentrations of UV-B-screening phenolics (flavonoids and phenolic acids) and low-UV-B-screening phenolics (salicylates and condensed tannins) in fresh leaves were investigated and the biomass of leaves, stems and roots was determined. As expected, the total amount of flavonoids in willow leaves clearly increased when plantlets were exposed to higher UV-B irradiation. However, the degree of increase of individual compounds varied: luteolin-7-glucoside, monomethyl-monocoumaryl-luteolin-7-glucoside and one myricetin derivative increased significantly, while the apigenin-7-glucuronide increased only slightly. The enhanced UV-B also increased the amount of p -hydroxycinnamic acid derivative. The UV-B effects on other phenolic acids and tannins were minor. In contrast to the other phenolics, the amounts of two salicylates, salicin and saligenin, decreased under enhanced UV-B irradiation. Our results indicate that the concentrations of both UV-B-screening and low-UV-B-screening phenolic compounds in leaves of S. myrsinifolia may vary in response to elevated UV-B radiation. However, while the UV-B protective flavonoids and phenolic acids accumulate during UV-B exposure, the concentrations of certain salicylates decrease.     

Fine mapping of Hyplip1 and the human homolog, a potential locus for FCHL

Familial combined hyperlipidemia (FCHL) is a common genetic dyslipidemia predisposing to premature coronary heart disease (CHD). We previously identified a locus for FCHL on human Chromosome (Chr) 1q21-q23 in 31 Finnish FCHL families. We also mapped a gene for combined hyperlipidemia (Hyplip1) to a potentially orthologous region of mouse Chr 3 in the HcB-19/Dem mouse model of FCHL. The human FCHL locus was, however, originally mapped about 5 Mb telomeric to the synteny border, the centromeric part of which is homologous to mouse Chr 3 and the telomeric part to mouse Chr 1. To further localize the human Hyplip1 homolog and estimate its distance from the peak linkage markers, we fine-mapped the Hyplip1 locus and defined the borders of the region of conserved synteny between human and mouse. This involved establishing a physical map of a bacterial artificial chromosome (BAC) contig across the Hyplip1 locus and hybridizing a set of BACs to both human and mouse chromosomes by fluorescence in situ hybridization (FISH). We narrowed the location of the mouse Hyplip1 gene to a 1.5-cM region that is homologous only with human 1q21 and within approximately 5–10 Mb of the peak marker for linkage to FCHL. FCHL is a complex disorder and this distance may, thus, reflect the well-known problems hampering the mapping of complex disorders. Further studies identifying and sequencing the Hyplip1 gene will show whether the same gene predisposes to hyperlipidemia in human and mouse. Received: 9 September 2000 / Accepted: 30 October 2000     

Respiratory distress syndrome: evaluation of genetic susceptibility and protection by transmission disequilibrium test

Based on epidemiological data and genetic association studies, neonatal respiratory distress syndrome (RDS) is a complex disease with a multigenic background. The genes coding for surfactant proteins (SP) A and B have been assigned as the most likely genes in the etiology of RDS. The major factor predisposing to RDS is prematurity, and thus the phenotype of a very premature newborn infant that does not develop the disease can be regarded as hypernormal. Altogether 107 father-mother-offspring trios were divided into two sets according to the proband's phenotype, to evaluate familial segregation of candidate gene polymorphisms by the transmission disequilibrium test. A set of 76 trios were analyzed for transmission disequilibrium from parents to affected offspring. Another set of 31 trios were studied for allele transmission from parents to hypernormal offspring born very prematurely before the gestational age of 32 weeks. SP-A1-A2 haplotype 6A(2)-1A(0) showed significant excess transmission to affected infants and SP-A1 allele 6A(2) decreased transmission to the hypernormals. The present family study provides strong support for a direct or indirect role of the SP-A alleles as genetic predisposers to RDS in premature infants. The inclusion of parent-hypernormal offspring trios in transmission disequilibrium test is a useful approach to test for genetic protection against a disease.     

Expression of genes involved in anthocyanin biosynthesis in relation to anthocyanin,proanthocyanidin, and flavonol levels during bilberry fruit development

The production of anthocyanins in fruit tissues is highly controlled at the developmental level. We have studied the expression of flavonoid biosynthesis genes during the development of bilberry (Vaccinium myrtillus) fruit in relation to the accumulation of anthocyanins, proanthocyanidins, and flavonols in wild berries and in color mutants of bilberry. The cDNA fragments of five genes from the flavonoid pathway, phenylalanine ammonia-lyase, chalcone synthase, flavanone 3-hydroxylase, dihydroflavonol 4-reductase, and anthocyanidin synthase, were isolated from bilberry using the polymerase chain reaction technique, sequenced, and labeled with a digoxigenin-dUTP label. These homologous probes were used for determining the expression of the flavonoid pathway genes in bilberries. The contents of anthocyanins, proanthocyanidins, and flavonols in ripening bilberries were analyzed with high-performance liquid chromatography-diode array detector and were identified using a mass spectrometry interface. Our results demonstrate a correlation between anthocyanin accumulation and expression of the flavonoid pathway genes during the ripening of berries. At the early stages of berry development, procyanidins and quercetin were the major flavonoids, but the levels decreased dramatically during the progress of ripening. During the later stages of ripening, the content of anthocyanins increased strongly and they were the major flavonoids in the ripe berry. The expression of flavonoid pathway genes in the color mutants of bilberry was reduced. A connection between flavonol and anthocyanin synthesis in bilberry was detected in this study and also in previous data collected from flavonol and anthocyanin analyses from other fruits. In accordance with this, models for the connection between flavonol and anthocyanin syntheses in fruit tissues are presented.     

Role of hypusinated eukaryotic translation initiation factor 5A in polyamine depletion-induced cytostasis

We have earlier shown that alpha-methylated spermidine and spermine analogues rescue cells from polyamine depletion-induced growth inhibition and maintain pancreatic integrity under severe polyamine deprivation. However, because alpha-methylspermidine can serve as a precursor of hypusine, an integral part of functional eukaryotic translation initiation factor 5A required for cell proliferation, and because alpha, omega-bismethylspermine can be converted to methylspermidine, it is not entirely clear whether the restoration of cell growth is actually attributable to hypusine formed from these polyamine analogues. Here, we have used optically active isomers of methylated spermidine and spermine and show that polyamine depletion-induced acute cytostasis in cultured cells could be reversed by all the isomers of the methylpolyamines irrespective of whether they served or not as precursors of hypusine. In transgenic rats with activated polyamine catabolism, all the isomers similarly restored liver regeneration and reduced plasma alpha-amylase activity associated with induced pancreatitis. Under the above experimental conditions, the (S, S)- but not the (R, R)-isomer of bismethylspermine was converted to methylspermidine apparently through the action of spermine oxidase strongly preferring the (S, S)-isomer. Of the analogues, however, only (S)-methylspermidine sustained cell growth during prolonged (more than 1 week) inhibition of polyamine biosynthesis. It was also the only isomer efficiently converted to hypusine, indicating that deoxyhypusine synthase likewise possesses hidden stereospecificity. Taken together, the results show that growth inhibition in response to polyamine depletion involves two phases, an acute and a late hypusine-dependent phase.     

Distribution of Immunoreactive Prolyl Oligopeptidase in Human and Rat Brain

Prolyl oligopeptidase (POP) is a serine endoprotease that hydrolyses peptides shorter than 30-mer. POP may have a role in inositol 1,4,5-triphosphate (IP₃) signaling and in the actions of antidepressants, and POP inhibitors have exhibited antiamnesic and neuroprotective properties. However, little is known about the distribution of POP protein in the brain. We used immunohistochemistry to localize POP enzyme in the human whole hemisphere and in the rat whole brain. In humans, the highest POP densities were observed in caudate nucleus and putamen, hippocampus and cortex. In the rat, the highest POP densities were found in substantia nigra, hippocampus, cerebellum and caudate putamen. In general, the distribution of POP in human and rat brains was very similar and resembled that of IP₃ receptors. Our findings are support for a role of POP in movement regulation, cognition and possibly in IP₃ signaling. The expression of POP in processing nuclei further supports its function beyond neuropeptide metabolism. Dr. Erkki Tupala M.D. sadly passed away during the research project.     

Ectomycorrhiza,Friend or Foe?

Ecosystems - Many ecology textbooks present the interaction between mycorrhizal fungi and their host plants as the archetype of symbiosis or mutualism. However, mycorrhiza drains carbon directly...