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Biomedical subjects

D A Phillips

Publications and source records attributed to D A Phillips.

108 records · Page 6Linked to original sources
PubMed1977

Induction of Root Nodule Senescence by Combined Nitrogen in Pisum sativum L.

Root nodule senescence induced by nitrate and ammonium in Pisum sativum L. was defined by determining nitrogenase activity and leghemoglobin content with the acetylene reduction and pyridine hemochrome assays. Root systems supplied with 100 mm KNO(3) or 100 mm NH(4)Cl exhibited a decrease in nitrogenase activity followed by a decline in leghemoglobin content. Increasing the CO(2) concentration from 0.000320 atm to 0.00120 atm had no effect on the time course of root nodule senescence when 20 mm KNO(3) was supplied to the roots; in vitro nitrate reductase activity was detected in leaves and roots, but not bacteroids. Nitrate appeared in leaves, roots, and the nodule cytosol fraction but not bacteroids when 20 mm KNO(3) was supplied to roots. When nitrate entered through the shoots, however, no root nodule senescence was observed, and no nitrate was detected in root or nodule cytosol fractions although nitrate and nitrate reductase were found in leaves. The results suggest that nitrate does not induce root nodule senescence through competition between nitrate reductase and nitrogenase for products of photosynthesis.

Journal Article↗
PubMed1977

Ontogenetic Interactions between Photosynthesis and Symbiotic Nitrogen Fixation in Legumes.

Photosynthetic data collected from Pisum sativum L. and Phaseolus vulgaris L. plants at different stages of development were related to symbiotic N(2) fixation in the root nodules. The net carbon exchange rate of each leaf varied directly with carboxylation efficiency and inversely with the CO(2) compensation point. Net carbon exchange of the lowest leaves reputed to supply fixed carbon to root nodules declined in parallel with H(2) evolution from root nodules. The decrease in H(2) evolution also coincided with the onset of flowering but preceded the peak in N(2) fixation activity measured by acetylene-dependent ethylene production. A result of these changes was that the relative efficiency of N(2) fixation in peas increased to 0.7 from an initial value of 0.4. The data reveal that attempts to identify photosynthetic contributions of leaves to root nodules will require careful timing and suggest that the relative efficiency of N(2) fixation may be influenced by source-sink relationships.

Journal Article↗
PubMed1977

Effect of Light Intensity on Efficiency of Carbon Dioxide and Nitrogen Reduction in Pisum sativum L.

Photosynthetic efficiency, primary productivity, and N(2) reduction were determined in peas (Pisum sativum L. var. Alaska) grown at light intensities ranging from severely limiting to saturating. Plants grown under higher light intensities showed greater carboxylation and light capture potential and higher rates of net C exchange. Uptake of N(2), computed from measured C(2)H(2) reduction and H(2) evolution rates, also increased with growth light intensity, while the previously proposed relative efficiency of N(2) fixation, based on these same parameters, declined. The plot of N/C ratios (total nitrogen content/plant dry weight) increased hyperbolically with light intensity, and the plot of N(2)/CO(2) uptake ratios (N(2) uptake rate/net CO(2) uptake rate) increased linearly. Both plots extrapolated to the light compensation point. The data indicate that the relative efficiency of N(2) fixation is not necessarily correlated with maximum plant productivity and that evaluation of a plant's capacity to reduce N(2) is related directly to concurrent CO(2) reduction. A measure of whole plant N(2) fixation efficiency based on the N(2)/CO(2) uptake ratio is proposed.

Journal Article↗
PubMed1977

Angiography of nonfunctioning pheochromocytomas of the adrenal gland.

Two patients with clinically nonfunctioning pheochromocytomas of the adrenal gland were studied angiographically. The radiological characteristics were indistinguishable from those of functioning pheochromocytomas. In patients with hypervascular adrenal masses, the diagnosis of pheochromocytoma should be considered even in the absence of customary signs and symptoms.

Adrenal Gland Neoplasms↗
PubMed1976

Effect of protein additives on acetylene reduction (nitrogen fixation) by Rhizobium in the presence and absence of soybean cells.

The effect of protein additives on acetylene reduction (N(2) fixation) by Rhizobium associated with soybean cells (Glycine max [L.] Merr.) in vitro was studied. Acetylene reduction was promoted on the basal medium supplemented with 1.4 mg of N/ml supplied as aqueous extracts of hexane-extracted soybean, red kidney beans (Phaseolus vulgaris L.), or peas (Pisum sativum L.). Commercial samples of alpha-casein, or bovine serum albumin also promoted acetylene reduction at a concentration of 1.4 mg of N/ml of basal medium, but egg albumin supplying an equal amount of nitrogen to the basal medium completely suppressed acetylene reduction. Autoclaving the aqueous extract of hexane-extracted soybean meal had no effect on its ability to promote acetylene reduction. The presence of 40 mm succinate decreased acetylene reduction with leguminous proteins supplying 1.4 mg of N/ml but promoted acetylene reduction by Rhizobium 32H1-soybean cell associations on media containing alpha-casein, bovine serum albumin, or egg albumin suppling 1.4 mg of N/ml. Similar results were obtained with both cowpea Rhizobium 32H1 and Rhizobium japonicum 61A96. Pure cultures of Rhizobium 32H1 developed acetylene-reducing activity in the presence of soybean extract on basal agar medium and in vermiculite supplied with N-free mineral salts plus crude soybean meal. The results suggest that in certain situations, free living Rhizobium may reduce N(2) under field conditions.

Journal Article↗
PubMed1974

Factors affecting the reduction of acetylene by Rhizobium-soybean cell associations in vitro.

The acetylene reduction assay was used to measure presumed N(2)-reducing activity in Rhizobium-soybean cell associations in vitro. No acetylene reduction was observed in liquid suspensions of these organisms, but cells plated onto an agar medium from a liquid suspension of Rhizobium and soybean cells exhibited acetylene-dependent production of ethylene after 7 to 14 days. Aggregates of soybean cells 0.5 to 2.0 mm in diameter were required for this activity. Decreasing oxygen from 0.20 atm to 0.10, 0.04, or 0.00 atm completely inhibited acetylene reduction. The presence of 2,4-dichlorophenoxyacetic acid or kinetin increased endogenous ethylene production and inhibited acetylene-dependent ethylene production. Acetylene reduction was observed with three out of four strains of R. japonicum tested, and three rhizobial strains, which produce root nodules on cowpeas but not soybeans, formed an association capable of acetylene-dependent ethylene production.

Journal Article↗
PubMed1973

Isolation from Rhizobium for factors which transfer electrons to soybean nitrogenase.

Rhizobium japonicum grown anaerobically with nitrate produced several factors capable of transferring electrons from spinach chloroplasts lacking photosystem II to soybean root nodule nitrogenase. The same organism grown aerobically produced no factors with detectable activity. It is concluded that the bacterium is potentially capable of producing these proteins in the low oxygen conditions of the leguminous root nodule.

Journal Article↗
PubMed1972

Studies on cytokinin production by Rhizobium.

Cytokinin was released into the medium by cultures of both Rhizobium japonicum and R. leguminosarum. Calculations show that the amount of cytokinin released during the logarithmic phase of growth by R. japonicum would be sufficient to initiate the cortical cell divisions necessary to form a root nodule. The substance released by R. japonicum was identified as a zeatin-like compound on the basis of paper chromatography in four solvent systems. Two solvents clearly separated the rhizobial product from N(6)-Delta(2)-isopentenyladenine and its ribonucleoside. The predominant intracellular cytokinin found in both enzymatic hydrolysates of sRNA and alkaline hydrolysates of total RNA also was similar to zeatin.

Journal Article↗
PubMedDate not supplied

Effects of flavonoids released naturally from bean (Phaseolus vulgaris) on nodD-regulated gene transcription in Rhizobium leguminosarum bv. phaseoli.

Nine flavonoid aglycones released from black bean (Phaseolus vulgaris 'PI165426CS') seeds and roots induced nodC::lacZ transcription in Rhizobium leguminosarum bv. phaseoli strains containing extra cloned copies of the regulatory genes nodD1, nodD2, or nodD3 from that biovar. Individual flavonoids generally induced highest levels of nodC::lacZ transcription (Imax) with extra copies of nodD2, and the concentration required for half-maximum induction (I50) was lowest with extra copies of nodD1 genes. One apparently unique feature of R. l. bv. phaseoli is that naturally released flavonoids with very diverse structures induce nod genes. For all three nodD genes, two compounds exuded from roots, genistein and naringenin, produced much higher levels of nodC::lacZ transcription than other flavonoids, but this fact was not explained by increased transcription of the nodD genes themselves. The remaining seven flavonoid aglycones showed reproducibly different capacities to induce nodC::lacZ transcription, but all were considerably less powerful inducers than genistein and naringenin in strains with extra copies of each of the nodD genes. Tests with glycosides of the nod-gene inducers showed that glycosides, which are normally released by bean, had lower I50 values than the corresponding aglycones with all nodD genes. Additive interactions observed between the strong nod-gene inducer genistein and the weak inducer eriodictyol remain to be explained at the molecular level.

Bacterial Proteins↗
PubMedDate not supplied

Hemodynamic changes distal to selective arterial injections.

It has been assumed previously that the act of selectively injecting fluid through a catheter into an artery does not significantly alter hemodynamics in that vessel, provided open communication is maintained between the distal portion of the artery and the aortic lumen. In this study, blood flow was measured with an electromagnetic flow probe in distal branches of the left coronary or superior mesenteric arteries of 9 dogs while heparinized arterial blood was injected selectively into the parent vessels at varying rates up to 7 ml/sec. This resulted, in all experiments, in an abrupt and substantial rise in blood flow which was maintained for the duration of the injection. This phenomeon is due primarily to an increase in intraarterial pressure distal to the catheter tip, caused by the injection.

Angiography↗
PubMedDate not supplied

Balloon-occlusion superior mesenteric arteriography for improved visualization of the mesenteric and portal venous anatomy of dogs.

The superior mesenteric arteries of twelve dogs were occluded with an inflated balloon on the tip of an endhole catheter while diatrizoate meglumine and diatrizoate sodium (Renografin 76) was injected distal to the occlusion. The balloon was immediately deflated at the end of contrast injection. Films taken over a 33-second period showed consistently excellent visualization of the mesenteric arteries and veins as well as the portal veins. Comparison with studies performed by the conventional, nonocclusion technique confirmed the superiority of the films obtained with the balloon occlusion method. Histologic examination of the mesenteric artery at the site of balloon inflation and of the small and large bowel revealed no abnormalities.

Angiography↗
PubMedDate not supplied

Race and ethnicity as variables in Nursing Research, 1952-2000.

BACKGROUND: Although the use of race and ethnicity as variables in research has increased over the past five decades, there is confusion regarding the meaning of the terms, as well as how the words are defined and determined in scientific inquiry. OBJECTIVE: To review the use of race and ethnicity as variables in nursing research literature. METHODS: Original research articles published in Nursing Research in the years, 1952, 1955, and every 5 years thereafter through 2000 were reviewed. Those articles describing human characteristics (N = 337) were analyzed for content concerning: (a) frequency of racial and ethnic terms, (b) words used for racial and ethnic categories, (c) detinitions of racial and ethnic terms, and (d) how a study participant's race or ethnicity was determined. RESULTS: Racial and ethnic variables were mentioned in 167 of the 337 reviewed articles. Eighty-one terms and word phrases were used for these variables. In only five articles were the variables defined. Race and ethnic labels were often intermixed and the majority of studies provided no information about how categorization of the participant's race or ethnicity was made. In addition, there was relatively little growth in the number of studies that had racial/ethnic groups, other than Whites, as the majority of the sample. CONCLUSION: Racial and ethnic variables provide nurse researchers with many challenges. Although race and ethnicity were widely used in Nursing Research articles, the categories were not defined in the majority of papers, and methods used to determine a participant's race or ethnicity were unclear. In order to construct a common and consistent understanding of racial and ethnic categories, nurse researchers should be explicit regarding the rationale related to their use of the categories and the assumptions underlying particular racial and ethnic categorizations.

Bibliometrics↗
PubMedDate not supplied

Flaviviruses isolated from mosquitoes collected during the first recorded outbreak of Japanese encephalitis virus on Cape York Peninsula, Australia.

In response to an outbreak of Japanese encephalitis (JE) virus on Cape York Peninsula, Australia, in 1998, mosquitoes were collected using CO2 and octenol-baited Centers for Disease Control and Prevention light traps. A total of 35,235 adult mosquitoes, comprising 31 species, were processed for virus isolation. No isolates of JE virus were recovered from these mosquitoes. However, 18 isolates of Kokobera virus, another flavivirus were obtained from Culex annulirostris. Twelve isolates were from western Cape York (minimum infection rate (MIR) of 0.61: 1,000 mosquitoes) and 6 were from the Northern Peninsula Area (MIR of 1.0:1,000). Potential explanations for the failure to detect JE virus in mosquitoes collected from Cape York Peninsula include the timing of collections, the presence of alternative bloodmeal hosts, differences in pig husbandry, asynchronous porcine seroconversion, and the presence of other flaviviruses.

Animals↗