Search PubMed⌕ Search

Biomedical subjects

D A Phillips

Publications and source records attributed to D A Phillips.

At least 73 records · Page 4Linked to original sources
PubMed1989

Interactions among Flavonoid nod Gene Inducers Released from Alfalfa Seeds and Roots.

Alfalfa (Medicago sativa L.) seeds and roots can create complex rhizosphere effects by releasing flavonoids that induce nodulation (nod) genes in Rhizobium meliloti. Previous reports identified luteolin and 4,4'-dihydroxy-2'-methoxychalcone as strong inducers that are released from seeds and roots, respectively, and 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone as weaker inducers which are exuded by roots. As a first step toward identifying flavonoid interactions that may occur in the rhizosphere, combinations of these molecules were tested for transcriptional effects on a nodABC-lacZ fusion in R. meliloti. At low concentrations (e.g. 8.4 nanomolar), interactions of the three nod gene inducers from root exudate were additive. When the strong inducers 4,4'-dihydroxy-2'-methoxychalcone and luteolin were present separately at higher concentrations (e.g. 21 nanomolar), their effect could be decreased significantly by the weaker inducers 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone. In contrast, when low concentrations of luteolin from seed rinses and 4,4'-dihydroxy-2'-methoxychalcone from root exudate were present together, they produced synergistic increases in nod gene transcription. Tests with mixtures of the three nod gene inducers from root exudate indicated that alfalfa seedlings might easily decrease the strong inductive effect of the chalcone by releasing modest amounts of the weaker inducers. In addition, mixtures of luteolin and the nod gene inducers in root exudate suggested that interactions between nod gene inducers from seeds and roots may create a zone highly favorable to root nodule formation near the top of the primary root.

Journal Article↗
PubMed1989

A Chalcone and Two Related Flavonoids Released from Alfalfa Roots Induce nod Genes of Rhizobium meliloti.

Flavonoid signals from alfalfa (Medicago sativa L.) induce transcription of nodulation (nod) genes in Rhizobium meliloti. Previous investigations identified the flavone luteolin as an active inducer in alfalfa seed extracts, but the nature of nod inducers released from roots has not been reported. Root exudate from 3-day-old alfalfa seedlings was purified and then assayed for biological activity with a nodABC-lacZ fusion in R. meliloti. Indentities of major nod inducers were established by spectroscopic analyses (ultraviolet/visible, proton nuclear magnetic resonance, and mass spectroscopy) and comparison with authentic standards. Major nod inducers, which were identified as 4',7-dihydroxyflavone, 4'-7-dihydroxyflavanone, and 4,4'-dihydroxy-2'-methoxychalcone, were released from seedling roots at 54, 22, and 20 picomole.plant(-1).day(-1), respectively. Luteolin was not found in these root exudates. The 4,4'-dihydroxy-2'-methoxychalcone induced nod genes at a concentration one order of magnitude lower than luteolin and is the first naturally released chalcone reported to have this function. Moderate and weak nod-inducing activity was associated, respectively, with 4',7-dihydroxyflavone and 4',7-dihydroxyflavanone.

Journal Article↗
PubMed1989

Ergotism as a consequence of thromboembolic prophylaxis.

Vasospasm related to ergot intoxication is unusual. The authors report the case of 15-year-old boy who developed vasospasm necessitating amputation, due to an ergot derivative prescribed for thromboembolic prophylaxis. The importance of prompt angiographic recognition and therapy is stressed.

Adolescent↗
PubMed1988

The safety and angiographic efficacy of tissue plasminogen activator in a cerebral embolization model.

Thrombolysis with tissue plasminogen activator (tPA) has been used to treat myocardial infarction and pulmonary embolism in humans. This plasminogen activator may also be useful in treating certain strokes. We infused tPA or saline in rabbits 15 minutes after selective internal carotid artery embolization with 18-hour aged autologous clot. By serial angiography, the tPA-treated group demonstrated rapid angiographic reperfusion of the occluded vascular territory in 7 of 8 animals, whereas none of 6 saline controls did. None of the animals in either group developed macroscopic cerebral hemorrhage. Both groups showed cerebral infarction, predominantly in the territory of the occluded vessel; the extent of infarction did not differ between tPA-treated animals and controls. Early tPA therapy can allow reperfusion of occluded cerebral arteries safely and effectively in a rabbit cerebral embolization model.

Animals↗
PubMed1988

Selective embolization and clot dissolution with tPA in the internal carotid artery circulation of the rabbit.

We describe a model of thromboembolic stroke in rabbits that utilizes the Seldinger technique and digital arteriography. The internal carotid arteries of 14 rabbits were catheterized selectively and embolized with autologous blood clots. After embolization, eight rabbits received IV tissue plasminogen activator (tPA); the remaining six were infused with saline and served as controls. After embolization, cerebral arteriograms were obtained at 30-min intervals for 180 min. Cerebral arteriograms obtained after tPA therapy revealed partial or complete thrombus dissolution in seven (88%) of the eight treated rabbits. In the control group, none of the arteriograms of the embolized internal carotid arteries showed thrombus dissolution. In the tPA-treated group, the median time for thrombus dissolution was 60 min. This stroke model is economical, reproducible, and less traumatic to the brain than most of the previously described animal models. It also provides a means to compare the safety and efficacy of various thrombolytic agents in small animals.

Animals↗
PubMed1988

Pulmonary artery pseudoaneurysm. A potential complication of pulmonary artery catheterization.

A 70-year-old woman with pulmonary hypertension due to severe chronic obstructive pulmonary disease and long-standing mitral stenosis developed hemoptysis and a right upper lobe infiltrate during manipulation of a balloon-tipped flow-directed pulmonary artery catheter. Hemoptysis resolved spontaneously over several minutes, and the right upper lobe infiltrate cleared over several weeks, during which time a new right upper lobe nodule became apparent. Angiography disclosed the presence of a late-filling well-circumscribed saccular pseudoaneurysm. This was obliterated with an acute infiltrate with or without hemoptysis in the area subtended by a flow-director pulmonary artery catheter, and particularly when it is associated with manipulation of that catheter, the differential diagnosis should include pulmonary artery perforation as well as infarction. If the patient survives the episode, the possibility that a pseudoaneurysm has formed must be actively entertained and aggressively evaluated, since pseudoaneurysm is a potentially fatal lesion that is treatable.

Acute Disease↗
PubMed1987

Flavone limitations to root nodulation and symbiotic nitrogen fixation in alfalfa.

Transcription of the nodABC genes in Rhizobium meliloti is required for root nodule formation in alfalfa (Medicago sativa L.) and occurs when specific compounds, such as the flavone luteolin, are supplied by the host plant. Results reported here indicate how luteolin in the root and rhizosphere can affect subsequent N(2) fixation and plant growth. Previous experiments with ;Hairy Peruvian 32' (HP32), an alfalfa population produced from ;Hairy Peruvian' (HP) by two generations of selection for increased N(2) fixation and growth, found that HP32 had more root nodules and fixed more N(2) than the parental HP population. In the present study, flavonoid extracts of HP32 seedling roots are shown to contain a 60% higher concentration of compounds that induce transcription of a nodABC-lacZ fusion in R. meliloti than comparable extracts of HP roots. Chromatographic data indicated that HP32 roots had a 77% higher concentration of luteolin than HP roots. Adding 10 micromolar luteolin to the rhizosphere of HP seedlings increased nodulation, N(2) fixation, total N, and total dry weight but had no effect on nitrate assimilation. These data show that normal levels of flavone nodulation signals in the rhizosphere of HP alfalfa can limit root nodulation, symbiotic N(2) fixation, and seedling growth and suggest that one mechanism for increasing N(2) fixation can be the genetic enhancement of specific biochemical signals which induce nodulation genes in Rhizobium.

Journal Article↗
PubMed1987

Socialization of perceived academic competence among highly competent children.

A sample of 81 academically competent third graders and their parents were studied (1) to determine whether the illusion of incompetence documented for fifth graders appears in younger children, (2) to examine whether parents' competence-related perceptions significantly distinguish children with varying levels of perceived academic competence, and (3) to develop a predictive model of the association between parent and child competence beliefs. More than 20% of the children--equal proportions of girls and boys--had self-perceptions that seriously underestimated their actual high abilities, and displayed a corresponding pattern of disparaging self- and other-achievement attitudes. Mothers' and fathers' perceptions of their children's abilities varied significantly with the perceived competence status of the children, as did the children's perceptions of their parents' appraisals. Using path analysis, preliminary support was found for a model in which children's perceptions of competence are influenced more by their parents' appraisals than by objective evidence of their achievements. The results are discussed in the context of research on the socialization of math attitudes and new work on parental belief systems.

Achievement↗
PubMed1987

The clinical implications of bilaterally abnormal impedance plethysmography.

Although impedance plethysmography (IPG) is a test of recognized value in the diagnosis of acute proximal deep venous thrombosis (DVT), its meaning in patients with bilaterally abnormal IPGs is unclear. Consequently, we sought to determine the clinical significance of the bilaterally abnormal IPG in hospitalized patients. In a five-month prospective study, 19% (81/425) of all IPGs done at our institution were bilaterally abnormal (55% of all abnormal IPGs). Acute proximal DVT was found in 26% (14/53) of patients with bilaterally abnormal IPGs who underwent further diagnostic testing. Thirty-five percent of the patients with DVT were found to have either bilateral lower extremity DVT or clots in the inferior vena cava. A numerical score, the venous function index (VFI), was computed for the 101 legs for which further definitive diagnostic evaluations for DVT had been completed. The mean VFI of seven for legs with acute proximal DVT was significantly less than the mean VFI of 13 for legs with no DVT. Fifty percent of legs with a VFI less than or equal to five had DVT, whereas only 7% of legs with a VFI greater than 15 had DVT. The bilaterally abnormal IPG is a common clinical occurrence, is frequently associated with acute DVT, and the VFI is helpful in discriminating legs with acute proximal DVT from normal legs in patients with a bilaterally abnormal IPG.

Adolescent↗
PubMed1986

Sodium stimulation of uptake hydrogenase activity in symbiotic Rhizobium.

Initial observations showed a 100% increase in H(2)-uptake (Hup) activity of Rhizobium leguminosarum strain 3855 in pea root nodules (Pisum sativum L. cv Alaska) on plants growing in a baked clay substrate relative to those growing in vermiculite, and an investigation of nutrient factors responsible for the phenomenon was initiated. Significantly greater Hup activity was first measured in the clay-grown plants 24 days after germination, and higher activity was maintained relative to the vermiculite treatment until experiments were terminated at day 32. The increase in Hup activity was associated with a decrease in H(2) evolution for plants with comparable rates of acetylene reduction. Analyses of the clay showed that it contained more Na(+) (29 versus 9 milligrams per kilogram) and less K(+) (6 versus 74 milligrams per kilogram) than the vermiculite. Analyses of plants, however, showed a large increase in Na(+) concentration of clay-grown plants with a much smaller reduction in K(+) concentration. In tests with the same organisms in a hydroponic system with controlled pH, 40 millimolar NaCl increased Hup activity more than 100% over plants grown in solutions lacking NaCl. Plants with increased Hup activity, however, did not have greater net carbon or total nitrogen assimilation. KCl treatments from 5 to 80 millimolar produced slight increased in Hup activity at 10 millimolar KCl, and tests with other salts in the hydroponic system indicated that only Na(+) strongly promoted Hup activity. Treating vermiculite with 50 millimolar NaCl increased Na(+) concentration in pea plant tissue and greatly promoted Hup activity of root nodules in a manner analogous to the original observation with the clay rooting medium. A wider generality of the phenomenon was suggested by demonstrating that exogenous Na(+) increased Hup activity of other R. leguminosarum strains and promoted Hup activity of R. meliloti strain B300 in alfalfa (Medicago sativa L.).

Journal Article↗
PubMed1986

Distribution of hydrogen-metabolizing bacteria in alfalfa field soil.

H(2) evolved by alfalfa root nodules during the process of N(2) fixation may be an important factor influencing the distribution of soil bacteria. To test this hypothesis under field conditions, over 700 bacterial isolates were obtained from fallow soil or from the 3-mm layer of soil surrounding alfalfa (Medicago sativa L.) root nodules, alfalfa roots, or bindweed (Convolvulus arvensis L.) roots. Bacteria were isolated under either aerobic or microaerophilic conditions and were tested for their capacity to metabolize H(2). Isolates showing net H(2) uptake and H(2) incorporation activity under laboratory conditions were assigned a Hup phenotype, whereas organisms with significant H(2) output capacity were designated as a Hout phenotype. Under aerobic isolation conditions two Hup isolates were obtained, whereas under microaerophilic conditions five Hup and two Hout isolates were found. The nine isolates differed on the basis of 24 standard bacteriological characteristics or fatty acid composition. Five of the nine organisms were isolated from soil around root nodules, whereas the other four were found distributed among the other three soil environments. On the basis of the microaerophilic isolations, 4.8% of the total procaryotic isolates from soil around root nodules were capable of oxidizing H(2), and 1.2% could produce H(2). Two of the Hup isolates were identified as Rhizobium meliloti by root nodulation tests, but the fact that none of the isolates reduced C(2)H(2) under the assay conditions suggested that the H(2) metabolism traits were associated with various hydrogenase systems rather than with nitrogenase activity. Results from this study support the concept that H(2) evolution by alfalfa root nodules has a significant effect on the surrounding microenvironment and influences the number and diversity of bacteria occupying that region.

Journal Article↗
PubMed1985

Uptake Hydrogenase Activity Determined by Plasmid pRL6JI in Rhizobium leguminosarum Does Not Increase Symbiotic Nitrogen Fixation.

Six mutants of Rhizobium leguminosarum 3855 lacking uptake hydrogenase activity (Hup phenotype) as a result of Tn5-mob mutagenesis of the hup-containing plasmid pRL6JI were tested for symbiotic performance on Pisum sativum L. and Vicia benghalensis L. Three pea cultivars and one vetch line, which induce four different levels of Hup activity in strain 3855, were grown to flowering under microbiologically controlled conditions in the absence of combined N. Direct Kjeldahl N measurements showed that in every case at least one Hup mutant fixed as much N(2) as the isogenic Hup strain. Measures of C(2)H(2) reduction, H(2) evolution, H(2) incorporation, and plant dry weight were consistent with the interpretation that the oxidation of H(2) produced by the nitrogenase enzyme complex was not necessarily associated with increased N(2) fixation in these symbiotic associations. Tests with a smaller subset of the Hup strains under four different root environments ranging from pH 5.0 to 8.2 likewise showed no significant advantage for the isogenic Hup strain. It was concluded that the improvements in symbiotic N(2) fixation produced by pRL6JI are associated with some trait other than the Hup phenotype.

Journal Article↗
PubMed1984

A variation in the origin of the posterior descending coronary artery.

A rare congenital variation in the origin of the posterior descending artery (PDA) is described. The PDA arose from a vascular ring formed by a normally occurring communication between the right coronary artery and the left circumflex artery within the atrioventricular groove, then traversed the inferior septum following a normal branching pattern. No significant coronary artery stenoses nor abnormalities in the physiological data were present, thus ruling out the possibility of the communication being a collateral vessel secondary to ischemia. Our patient's uncommon communication represents only the third reported case of such an occurrence.

Angiography↗
PubMed1984

A transmissible plant shoot factor promotes uptake hydrogenase activity in Rhizobium symbionts.

Shoot/root grafting studies showed organ and host cultivar effects on net H(2) evolution from Pisum sativum L. root nodules. Net H(2) evolution from those nodules represents the sum of H(2) formed by Rhizobium nitrogenase and H(2) oxidized by any uptake hydrogenase present in the bacteria. Grafts between pea cultivars ;JI1205' or ;Alaska' and ;Feltham First' in symbioses with R. leguminosarum 128C53 showed that shoots of both JI1205 and Alaska increased H(2) uptake significantly (P </= 0.05) in Feltham First root nodules. The same plants also had less net H(2) evolution at similar rates of C(2)H(2) reduction than plants formed by grafting Feltham First shoots on Feltham First roots. Although JI1205 and Alaska shoots increased H(2)-uptake activity of Feltham First root nodules 28 days after the graft was made, intermediate to high levels of H(2) uptake activity were still present in nodules on roots of both JI1205 and Alaska grafted to Feltham First shoots. These results indicate the presence of a transmissible shoot factor(s) which can increase uptake hydrogenase activity in a Rhizobium symbiont and show that root genotype also can influence that parameter.Parallel grafting experiments using the same pea cultivars in symbioses with R. leguminosarum strain 300, which lacks uptake hydrogenase activity, suggested that a transmissible shoot factor(s) altered H(2) formation from nitrogenase by changing the electron allocation coefficient of that enzyme complex.The root and shoot factor(s) detected in this study had no permanent effect on strain 128C53. Bacterial cells isolated from Feltham First nodules with low H(2) uptake activity formed root nodules on JI1205 and Alaska with high H(2) uptake activity. Bacteroids isolated from nodules on intact JI1205, Alaska, or Feltham First plants with high, medium, or low H(2) uptake activity, respectively, maintained those phenotypes during in vitro assays.

Journal Article↗
PubMed1984

Effect of Plasmid pIJ1008 from Rhizobium leguminosarum on Symbiotic Function of Rhizobium meliloti.

Plasmid pIJ1008, which carries determinants for uptake hydrogenase (Hup) activity, was transferred from Rhizobium leguminosarum to Rhizobium meliloti without impairing the capacity of the latter species to form root nodules on alfalfa. The plasmid was still present in rhizobia reisolated from the root nodules of 12 different alfalfa cultivars, but only low levels of Hup activity were detected in alfalfa.

Journal Article↗
PubMed1983

Nitrogen Turnover and Assimilation during Regrowth in Trifolium subterraneum L. and Bromus mollis L.

Subterranean clover (Trifolium subterraneum L. cv Woogenellup) and soft chess grass (Bromus mollis L. cv Blando) were grown in monocultures with (15)NH(4)Cl added to the soil to study nitrogen movement during regrowth following shoot removal. Four clipping treatments were imposed. Essentially all available (15)N was assimilated from the soil prior to the first shoot harvest. Measurements of total reduced nitrogen and (15)N contained within that nitrogen fraction in roots, crowns, and shoots at each harvest showed large, significant (P </= 0.001) declines in excess (15)N of crowns and roots in both species between the first and fourth harvests. There was no significant decline in total reduced nitrogen in the same organs over that period. Similar responses were evident in plants defoliated three times. The simplest interpretation of these data is that reduced nitrogen compounds turn over in plant roots and crowns during shoot regrowth. Calculations for grass and clover plants clipped four times during the growing season indicated that 100 to 143% of the nitrogen present in crowns and roots turned over between the first and fourth shoot harvest in both species, assuming nitrogen in those organs was replaced with nitrogen containing the lowest available concentration of (15)N. If other potential sources of nitrogen were used for the calculations, it was necessary to postulate that larger amounts of total nitrogen flowed through the crown and root to produce the measured dilution of (15)N compounds. These data provide the first quantitative estimates of the amount of internal nitrogen used by plants, in addition to soil nitrogen or N(2), to regenerate shoots after defoliation.

Journal Article↗