PubMed Health⌕ Search

Biomedical subjects

J K Nielsen

Publications and source records attributed to J K Nielsen.

At least 19 recordsLinked to original sources
PubMed2001

Resistance to an herbivore through engineered cyanogenic glucoside synthesis.

The entire pathway for synthesis of the tyrosine-derived cyanogenic glucoside dhurrin has been transferred from Sorghum bicolor to Arabidopsis thaliana. Here, we document that genetically engineered plants are able to synthesize and store large amounts of new natural products. The presence of dhurrin in the transgenic A. thaliana plants confers resistance to the flea beetle Phyllotreta nemorum, which is a natural pest of other members of the crucifer group, demonstrating the potential utility of cyanogenic glucosides in plant defense.

Animals↗
PubMed2001

Degradation of phenanthrene-analogue azaarenes by Mycobacterium gilvum strain LB307T under aerobic conditions.

A polycyclic aromatic hydrocarbon degrading Mycobacterium gilvum, strain LB307T, was able to degrade the azaarenes 5,6-benzoquinoline, 7,8-benzoquinoline, and phenanthridine (nitrogen-containing heterocyclic aromatic hydrocarbons) under aerobic conditions. The strain was able to use 5,6-benzoquinoline as sole sources of carbon, nitrogen, and energy. However, inhibition of degradation and growth was observed with increasing substrate concentration. During degradation, metabolites built up transiently. One of the metabolites detected during 5,6-benzoquinoline degradation is suggested to be 2-oxo-5,6-benzoquinoline. This is the first report on bacterial degradation of phenanthrene-analogue azaarenes.

Aerobiosis↗
PubMed2001

Seasonal variation in leaf glucosinolates and insect resistance in two types of Barbarea vulgaris ssp. arcuata.

Leaves from natural populations of Barbarea vulgaris ssp. arcuata (Brassicaceae) in Denmark were examined for glucosinolate content and resistance to the crucifer specialist flea beetle Phyllotreta nemorum. Two types of the plant (P- and G-type) could be recognized. Leaves of the G-type contained the glucosinolates (only side chains mentioned): (S)-2-hydroxy-2-phenylethyl- (2S), indol-3-ylmethyl- (4) and in trace amount (R)-2-hydroxy-2-phenylethyl- (2R), 2-phenylethyl- (1) and 4-methoxyindol-3-ylmethyl- (5). Leaves of the P-type were dominated by 2R and 4, and had only trace amounts of 1, 2S, and 5 but contained in addition the previously unknown (R)-2-hydroxy-2-(4-hydroxyphenyl)ethyl- (3R). The epimer, (S)-2-hydroxy-2-(4-hydroxyphenyl)ethyl- (3S) was found in populations believed to be hybrids, and in B. orthoceras. 2S, 2R, desulfo 2S,-2R, -3S and -3R were isolated and identified by NMR and MS. Acylated glucosinolates or allylglucosinolate were not detected in leaves. The glucosinolate content in August was variable, 3-46 micromol/g dry wt, but was low in most populations, 3-15 micromol/g dry wt. In general, the glucosinolate content increased during the autumn, to 35-75 micromol/g dry wt in November. The G-type was resistant to neonate larvae of Phyllotreta nemorum in August and September (survival in 3-day bioassay typically 0%), and gradually lost the resistance in October and November (survival in 3-day bioassay 40-90%), and there was no correlation between glucosinolate content and resistance. Neither did glucosinolates explain the difference in resistance between the P-type (always susceptible) and the G-type (resistant in the summer season).

Acylation↗
PubMed2001

1,4-Dimethoxyglucobrassicin in Barbarea and 4-hydroxyglucobrassicin in Arabidopsis and Brassica.

A novel indole glucosinolate, 1,4-dimethoxyglucobrassicin (1,4-dimethoxyindol-3-ylmethylglucosinolate), was isolated as the desulfo derivative from roots of the P-type of Barbarea vulgaris ssp. arcuata, and its structure was determined by spectroscopy including 2D NMR spectroscopy. 4-Hydroxyglucobrassicin (4-hydroxyindol-3-ylmethylglucosinolate) was isolated as the desulfo derivative from green siliques (fruits) of Arabidopsis thaliana and identified by comparison of its (1)H NMR spectrum with the spectrum of the known desulfoglucosinolate from Brassica napus. The delayed elution of desulfo indole glucosinolates from the DEAE Sephadex column used in sample preparation was examined, and the diode-array UV spectra of desulfo indole glucosinolates were measured, to ensure a reliable determination of 1,4-dimethoxyglucobrassicin and 4-hydroxyglucobrassicin with the existing analysis method based on the HPLC of desulfoglucosinolates. 1,4-Dimethoxyglucobrassicin was not detected in 10 other Arabidopsis, Brassica, and Barbarea species, indicating an evolutionarily recent mutation in the indole glucosinolate biosynthesis in B. vulgaris ssp. arcuata type P.

Arabidopsis↗
PubMed2001

Demic structure and its relation with the distribution of an adaptive trait in Danish flea beetles.

The flea beetle Phyllotreta nemorum is an oligophagous species using crucifers as host plants. In Denmark two populations have been found which use Barbarea vulgaris ssp. arcuata (G-type) as a host plant, whereas this plant is unsuitable for the survival of the majority of P. nemorum. In the locations in which these two populations occur, alternative host plants are also present. The plants occur in patches, some of which contain a mixture of host plants. In this study of allozyme variation, genetic differentiation between P. nemorum using different host plants in patches in the two different localities was studied hierarchically to assess substructuring of the populations. Evidence was found for low, but significant, amounts of genetic differentiation between (sub)populations using spatially separated plant patches at a distance of approximately 100 m to 1 km (theta = 0.009) and between localities approximately 44 km apart (theta = 0.026), and there was an association between genetic differentiation and geographical distance. No genetic differentiation was found between beetles from different host plants with overlapping local distributions. No evidence was thus found for sympatric host race formation. The geographical distribution of genes enabling P. nemorum to use B. vulgaris as a host plant (100% 'resistant' beetles in samples from B. vulgaris, but much fewer on patches containing only alternative host plants) contrasts with the relatively low amount of genetic differentiation at the neutral allozyme loci. This distribution of 'resistant' beetles (to B. vulgaris defence) is likely to be influenced by local differences in selection and asymmetric gene flow.

Adaptation, Physiological↗
PubMed2000

Genetics of resistance against defences of the host plant Barbarea vulgaris in a Danish flea beetle population.

One essential aspect of the study of the evolution of host-plant use by insects is (variation in) its genetic basis. The genetic basis of the ability of a flea beetle (Phyllotreta nemorum) to use the crucifer Barbarea vulgaris ssp. arcuata (G type) as a host plant was studied in a Danish population (Kvaerkeby) occurring naturally on this atypical host plant. Evidence was found that this ability was determined by a single, major, autosomal gene, although the presence of genes at additional loci at lower frequencies could not be excluded. No evidence was found for sex-linked inheritance, which was common in a second population in Denmark (Ejby) using Barbarea as a host plant. All beetles in the Kvaerkeby sample were homozygous 'resistant' to Barbarea defence. After crossing resistant F1 offspring from pairs consisting of a field-collected beetle and a susceptible one amongst each other, genotyping the F2 (reared on radish) showed a 1:2:1 ratio of homozygous resistant, heterozygous and susceptible beetles. No evidence was found for a reduction in the viability of beetles that were homozygous resistant at the autosomal locus, in contrast to what had been found earlier for two backcrossed lines founded by beetles from Ejby. The results show that there is variation in the genetic basis of host-plant use across local populations and imply that population structure should form part of the study of the interaction between P. nemorum and its host plants.

Animals↗
PubMed2000

Synthesis of FF-MAS from lithocholic acid.

An effective synthesis of 4,4 dimethyl-cholest-8,14,24-trien-3beta-ol (FF-MAS) from lithocholic acid is described, utilising a double oxidation and regioselective Wittig reaction as key steps.

Biochemistry↗
PubMed2000

Reduction in fitness of flea beetles which are homozygous for an autosomal gene conferring resistance to defences in Barbarea vulgaris.

Major resistance genes are present in Danish flea beetle (Phyllotreta nemorum) populations, enabling the beetles to utilize a defended plant, Barbarea vulgaris ssp. arcuata, as a host plant, whereas this plant is unsuitable for beetles lacking the resistance genes. Two lines of beetles carrying a resistance gene have been established which are near-isogenic with a susceptible line. Larval survival of offspring from crosses between flea beetles carrying resistance genes and susceptible beetles, tested in bioassays on the defended B. vulgaris, and sex ratios of the survivors, were consistent with the presence of a dominant, autosomal resistance gene in each of the lines. An attempt to produce pure-breeding lines for the autosomal genes revealed that beetles that are homozygous for the resistance gene suffer a high mortality. This result was repeatable for both lines, and when both resistant males and females were used in the crosses. The high mortality was also independent of the plant (defended B. vulgaris or suitable radish) on which the beetles were reared. The results suggest that the time of death of homozygous resistant beetles is variable. The spread and maintenance of resistance genes in flea beetle populations are discussed.

Animals↗
PubMed1998

Kaempferol tetraglucosides from cabbage leaves.

Four flavonol glycosides were isolated from a leaf extract of cabbage and characterized by chemical and spectroscopic methods including 1H and 13C NMR and negative ion FAB-MS. The common structure of the four compounds was kaempferol 3-O-beta-D-[beta-D-glucopyranosyl(1-->2)glucopyranoside]-7- O-beta-D-[beta-D-glucopyranosyl(1-->4)glucopyranoside]. This compound was found unmodified or acylated at C-2"' (outer glucose in sophorosyl moiety) with either sinapic acid, ferulic acid or caffeic acid. The possible role of diversity in glycosylation and acylation patterns of flavonol glycosides for plant defences against herbivores is discussed.

Brassica↗
PubMed1998

[Decisions about life and death. An empirical study of the position of Danish physicians concerning end-of-life decisions].

In a postal questionnaire investigation of experiences and attitudes concerning end-of-life decisions among Danish physicians, most of the respondents reported having made decisions involving the hastening of a patient's death, and considered this acceptable. Such decisions were more frequent, and were considered ethically more acceptable, when made with the patient's informed consent than without. Of the respondents, two per cent had participated in assisted suicide, and five per cent had administered a lethal injection at the patient's request, practices considered ethically acceptable by 37 per cent and 34 per cent, respectively, of the respondents. The most frequently cited reasons for opposing such practices were double effect principle, the active killing/allowed-death distinction, and the sanctity of life; and the most frequently cited justifications were respect for the patient's autonomy, the avoidance of unnecessary suffering, and the patient's right to a death with dignity.

Decision Making↗
PubMed1997

[Cervical extraosseous Ewing sarcoma].

A case of extraosseous Ewing's sarcoma is presented. The clinical, morphological and imaging characteristics of this rare neoplasm are briefly discussed.

Adult↗
PubMed1996

Pemoline therapy in college students with attention deficit hyperactivity disorder: a retrospective study.

Pemoline, a dopamine agonist, is effective in children with attention deficit hyperactivity disorder (ADHD), but its efficacy in adults is unknown. The authors studied the efficacy and safety of pemoline, using retrospective chart review of treated students with ADHD over a 2-year period. Forty students met diagnostic and treatment criteria; pemoline was associated with much improved or very much improved Clinical Global Impression symptoms scores in 70% of the students during a treatment period of 14 or more days. Severity of illness scores dropped from 4.11 to 3.01 between baseline and subsequent evaluation. Nine evaluable patients had adverse events, most commonly headaches, insomnia, and decreased appetite. Five additional students, who failed to meet the treatment-duration criterion, terminated because of severe initial insomnia. The authors concluded that pemoline is effective and safe in students with ADHD and has a lower abuse potential than methylphenidate and dextroamphetamine, the other two widely used, structurally dissimilar compounds, but controlled studies may be necessary before any final conclusions are reached.

Adolescent↗
PubMed1993

Acylated flavonol glycosides from cabbage leaves.

Seven flavonol glycosides were isolated from a leaf extract of cabbage and characterized by chemical and spectroscopic methods including 1H and 13C NMR and negative ion FAB-MS. Five compounds were new natural products or were fully characterized for the first time. They are derivatives of kaempferol-3-O-beta-D-sophoroside-7-O-beta-D-glucoside acylated at C-2"' with either caffeic acid, p-coumaric acid or ferulic acid, and of quercetin-3-O-beta-D-sophoroside-7-O-beta-D-glucoside acylated with either caffeic acid or ferulic acid. Kaempferol-3-O-beta-D- sophoroside-7-O-beta-D-glucoside and kaempferol-3-O-beta-D-(2-sinapoylsophoroside)-7-O-beta-D-glucoside were found for the first time in cabbage, but they have previously been found in other Brassica species.

Brassica↗
PubMed1992

[Septic cavernous sinus thrombosis after nasal surgery].

A case of septic cavernous sinus thrombosis after surgical removal of nasal polyps is presented. To the best of our knowledge, this is the second report of this rare and serious complication of nasal surgery. The clinical features are briefly discussed and the importance of early diagnosis and treatment is emphasized.

Aged↗
PubMed1990

Unusual effects of the ionophore A23187 at suboptimal concentrations in mast cell histamine release.

Certain peculiarities are observed in connection with histamine release induced by suboptimal concentrations of the ionophore A23187. The potency of the ionophore can increase by a factor of 3 when added to the incubation medium from solutions in either DMSO or buffer without added calcium as compared with addition from standard buffer. The effect was not due to the solvent per se but may relate to physicochemical conditions facilitating the ionophore's access to cellular domains.

Animals↗
PubMed1990

Influence of TMB-8 and calmidazolium on phorbol ester promoted histamine release from isolated rat mast cells.

The effects of TMB-8 and calmidazolium were investigated on mast cell responses believed to be mediated by protein kinase C, i.e. histamine release induced by TPA (tetradecanoyl-phorbol-acetate) in combination with sub-threshold concentrations of the ionophore A23187 and with antigen. Inhibition with both drugs was found in the same concentration range as observed earlier and could be counteracted by glucose, indicating an impaired oxidative energy production. Hence, the test drugs do not reveal protein kinase C selectivity.

Animals↗