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Biomedical subjects

E Zeiger

Publications and source records attributed to E Zeiger.

At least 145 records · Page 8Linked to original sources
PubMed1983

Gas exchange in paphiopedilum: lack of chloroplasts in guard cells correlates with low stomatal conductance.

Net photosynthesis and stomatal conductance were measured in attached leaves of Paphiopedilum insigne. At 20 degrees C and a vapor-pressure deficit of 0.5 kilopascal, both net photosynthesis and stomatal conductance were light-saturated below 0.2 millimole per square meter per second, a response typical of shade plants. The absolute values of photosynthetic rate and conductance however were remarkably low, presumably reflecting an adaptation to the low-light, limited-nutrient habitat characteristic of these orchids. The leaves also showed a vapor-pressure deficit response, with net photosynthesis and conductance varying over a 2-fold range between 0.3 and 1.6 kilopascals.These results confirm that Paphiopedilum stomata are functional. The correlation between achlorophyllous guard cells and low conductance rates, however, singles them out as an exceptional biological system, exhibiting basic differences from typical stomata in higher plants. Available evidence showing that guard-cell chloroplasts are needed to sustain high conductance rates at moderate to high irradiances indicates that the genetic changes leading to the loss of chloroplast differentiation in Paphiopedilum guard cells were not deleterious because of the low conductance rates characteristic of this genus.

Journal Article↗
PubMed1983

Regulation of ADPGlucose Synthesis in Guard Cells of Commelina communis.

The activator specificity of the ADPglucose pyrophosphorylase from Commelina communis guard cells is the same as observed for the mesophyll cell enzyme. 3-Phosphoglycerate was found to be the most effective activator. Fifty per cent of maximal stimulation was observed at about 100 micromolar. Inorganic phosphate was found to be a potent inhibitor giving 50% inhibition at 0.3 millimolar. These results are discussed with respect to regulation of starch synthesis in guard cells.

Journal Article↗
PubMed1983

Migration of detachable mini-balloon from the ICA causing occlusion of the MCA. Case report.

This patient had an aneurysm on the internal carotid artery that was responsible for episodes of severe hemorrhage through the nose. During occlusion of the aneurysm by a detachable balloon, the balloon became dislodged and migrated, obstructing the middle cerebral artery territory and causing a life-threatening situation. This was treated promptly and successfully by removal of the balloon and repair of the artery. Attention is drawn to the risk of such migration occurring, and the possible causes.

Adult↗
PubMed1983

Activation of some aromatic amines to mutagenic products by prostaglandin endoperoxide synthetase.

Cooxidation of xenobiotics may occur during prostaglandin biosynthesis. The ability of prostaglandin endoperoxide synthetase to cooxidize several aromatic amines and other chemicals to mutagenic products was tested with the standard Salmonella tester strains. The microsomal fraction of ram seminal vesicles, a rich source of prostaglandin endoperoxide synthetase, in the presence of the prostaglandin endoperoxide synthetase substrate arachidonic acid metabolized benzidine, 2-aminofluorene, 2-naphthylamine, and 2,5-diaminoanisole to mutagenic products. 1-Napthylamine, 2-aminoanthracene, 2-acetylaminofluorene, and 2,4-diaminoanisole were negative or weakly mutagenic. N-Nitrosodimethylamine, N-nitrosomorpholine, the pesticide Aminocarb, and di(2-ethylhexyl)phthalate were not activated to mutagenic products by the ram seminal vesicle microsomal fraction.

Amines↗
PubMed1982

Structure-activity studies on the mutagenicity of tris(2,3-dibromopropyl) phosphate (Tris-BP) and its metabolites in Salmonella.

A series of methylated metabolites of the flame retardant tris(2,3-dibromopropyl) phosphate (Tris-BP) were tested for mutagenicity in Salmonella, along with the parent chemical and other structurally related chemicals. The metabolites produced a gradient of mutagenic responses in TA1535 in the same dose range and up to the same magnitude as the Tris-BP response. None of the metabolites tested appeared to be the ultimate mutagen, since they all required S-9 for their mutagenic activity.

Animals↗
PubMed1982

Mutagenicity of (R) and (S) styrene 7,8-oxide and the intermediary mercapturic acid metabolites formed from styrene 7,8-oxide.

We have tested the two enantiomers of styrene 7,8-oxide and various thioether metabolites of racemic styrene 7,8-oxide for their direct mutagenicity in Salmonella typhimurium TA100. The mutagenicity data suggests that the (R) enantiomer is more mutagenic than the (S) enantiomer, with the racemic mixture intermediate between the two. The thioether metabolites were not mutagenic. The difference in the mutagenicities of enantiomers probably resulted from a stereoselective process in the Salmonella tester strain. At the present time it is not clear whether the rate-limiting reaction is the interaction of the enantiomers with DNA or some other cellular component.

DNA, Bacterial↗
PubMed1982

Mutagenicity and DNA-modifying activity of 2-nitropropane.

The results presented herein confirm the mutagenicity in Salmonella of 2-nitropropane and the relative inactivity of 1-nitropropane. The lack of mutagenicity of 1- and 2-aminopropane is also reported. In addition, we have demonstrated the in vitro DNA-modifying activity of 2-nitropropane, and present evidence to suggest that genetic activity of this nitroalkane may not be dependent on the enzymic reduction of the nitro function to the corresponding hydroxylamine.

Alkanes↗
PubMed1982

Chlorophyll a Fluorescence Transients in Mesophyll and Guard Cells : MODULATION OF GUARD CELL PHOTOPHOSPHORYLATION BY CO(2).

Chlorophyll fluorescence transients from mesophyll and guard cell chloroplasts of variegated leaves from Chlorophytum comosum were compared using high resolution fluorescence spectroscopy. Like their mesophyll counterparts, guard cell chloroplasts showed the OPS fluorescence transient indicating the operation of the linear electron transport and the possible generation of NADPH in these organelles. They also showed a slow fluorescence yield decrease, equivalent to the MT transition in mesophyll, suggesting the formation of the high energy state and photophosphorylation. Unlike the mesophyll chloroplasts, the fluorescence from guard cell chloroplasts lacked the increment of the SM transition, indicating that the two types of chloroplasts have some metabolic differences. The presence of CO(2) (supplied as bicarbonate, pH 6.7) specifically inhibited the MT-equivalent transition while its absence accelerated it. These observations constitute the first specific evidence of a guard cell chloroplast response to CO(2). Control of photosynthetic ATP levels in the guard cell cytoplasm by CO(2) may provide a mechanism regulating the availability of high energy equivalents at the guard cell plasmalemma, thus affecting stomatal opening.

Journal Article↗
PubMed1982

Photocontrol of the Functional Coupling between Photosynthesis and Stomatal Conductance in the Intact Leaf : Blue Light and Par-Dependent Photosystems in Guard Cells.

The photocontrol of the functional coupling between photosynthesis and stomatal conductance in the leaf was investigated in gas exchange experiments using monochromatic light provided by lasers. Net photosynthesis and stomatal conductance were measured in attached leaves of Malva parviflora L. as a function of photon irradiance at 457.9 and 640.0 nanometers.Photosynthetic rates and quantum yields of photosynthesis were higher under red light than under blue, on an absorbed or incident basis.Stomatal conductance was higher under blue than under red light at all intensities. Based on a calculated apparent photon efficiency of conductance, blue and red light had similar effects on conductance at intensities higher than 0.02 millimoles per square meter per second, but blue light was several-fold more efficient at very low photon irradiances. Red light had no effect on conductance at photon irradiances below 0.02 millimoles per square meter per second. These observations support the hypothesis that stomatal conductance is modulated by two photosystems: a blue light-dependent one, driving stomatal opening at low light intensities and a photosynthetically active radiation (PAR)-dependent one operating at higher irradiances.When low intensity blue light was used to illuminate a leaf already irradiated with high intensity, 640 nanometers light, the leaf exhibited substantial increases in stomatal conductance. Net photosynthesis changed only slightly. Additional far-red light increased net photosynthesis without affecting stomatal conductance. These observations indicate that under conditions where the PAR-dependent system is driven by high intensity red light, the blue light-dependent system has an additive effect on stomatal conductance.The wavelength dependence of photosynthesis and stomatal conductance demonstrates that these processes are not obligatorily coupled and can be controlled by light, independent of prevailing levels of intercellular CO(2). The blue light-dependent system in the guard cells may function as a specific light sensor while the PAR-dependent system supplies a CO(2)-modulated energy source providing functional coupling between the guard cells and the photosynthesizing mesophyll.

Journal Article↗
PubMed1982

Selective activation of some dihydrodiols of several polycyclic aromatic hydrocarbons to mutagenic products by prostaglandin synthetase.

The ability of prostaglandin synthetase (PGS) to cooxidize benzo(a)pyrene, benzo(a)anthracene, chrysene, and several of their dihydrodiol derivatives to mutagenic products was tested with Salmonella typhimurium strains TA98 and TA100. The microsomal fraction of ram seminal vesicles, a known source of PGS, in the presence of the PGS substrate arachidonic acid, metabolized benzo(a)pyrene-7,8-dihydrodiol, benzo(a)anthracene-3,4-dihydrodiol, and chrysene-1,2-dihydrodiol to mutagenic products. This activity was inhibited by the PGS inhibitor indomethacin. Unlike the PGS system, however, a cytochrome P-450-reduced nicotinamide adenine dinucleotide phosphate-dependent system, present in an Aroclor 1254-induced rat liver 9000 x g supernatant fraction, also activated the parent compounds [benzo(a)pyrene, benzo(a)anthracene, chrysene] and several other benzo(a)anthracene dihydrodiols (the 1,2-dihydrodiol, the 8,9-dihydrodiol, and the 10,11-dihydrodiol). The chrysene trans-3,4, trans-5,6, and cis-5,6 diols were not activated to mutagens by either system. Thus, the PGS system appears to be more selective than does the cytochrome P-450 system in the activation of polycyclic aromatic hydrocarbons to mutagenic products, activating only those dihydrodiols with adjacent double bonds in the bay region from which the bay-region diol-epoxides are formed.

Animals↗
PubMed1981

A rapid and simple scheme for confirmation of Salmonella tester strain phenotype.

A simple scheme has been developed for confirming the phenotype of the standard set of Salmonella typhimurium tester strains. This scheme employs a series of filter paper discs impregnated with diagnostic mutagens or bacterial toxins. Up to 6 diagnostic discs can be placed on a petri dish to test a single Salmonella strain. The Salmonellae are distinguished by their responses to ampicillin, crystal violet, nitrofuratoin, 9-aminoacridine, 4-nitro-o-phenylenediamine and sodium azide.

Bacteriological Techniques↗
PubMed1981

An evaluation of tests using DNA repair-deficient bacteria for predicting genotoxicity and carcinogenicity. A report of the U.S. EPA's Gene-TOX Program.

The detection of DNA-damaging agents by repair-deficient bacterial assays is based on the differential inhibition of growth of repair-proficient and repair-deficient bacterial pairs. The various methodologies used are described and recommendations are made for their improved use. In a survey of the literature through April 1979, 91 of 276 papers evaluated contained usable data, resulting in an analysis of 611 compounds that had been assayed in 1 or more of 55 pairs of repair-proficient and repair-deficient strains. The results indicate that (1) a liquid suspension assay is more sensitive than a spot (diffusion) test. In a review of the Escherichia coli polA assay, 45 compounds that gave "No Test" in the spot test were clearly positive or negative in the liquid suspension assay. (2) Of the 21 compounds analyzed by the E. coli polA assay and by other E. coli repair-deficient strains (e.g., rec, uvr, hcr, and exr derivatives of WP2 and AB1157), 10 were in complete agreement in all strains except uvrA strains. This indicates that strains other than polA+/polA- are useful for detecting DNA-damaging agents. However, in selecting strains for use in these assays, care should be taken to consider repair pathway specificity for particular compounds. (3) There was a 78% correspondence between results obtained with E. coli polA and Bacillus subtilis (H17/M45, 17A/45T) rec assay and between E. coli polA and Proteus mirabilis. (4) In a comparison of test results with carcinogenicity data, 44 of 71 (62%) carcinogenic compounds assayed by the polA system were positive, 10 (14%) were negative, and 17 (24%) gave No Test or doubtful results. 7 carcinogens were assayed by other E. coli strains and all were positive. 56 carcinogens were assayed in B. subtilis: 24 (43%) were positive, 9 (16%) were negative, and 23 (41%) gave No Test or doubtful results. Of the 7 carcinogens assayed in P. mirabilis, 6 (86%) were positive and 1 (14%) was negative. (5) The results were analyzed with respect to chemical classes. E. coli polA detected the highest percentage of hydroxylamines and alkyl epoxides. The B. subtilis rec assay detected the highest percentage of nitrosamines and sulfur and nitrogen oxides. It is concluded that some of these test systems are effective tools for the detection of DNA-damaging and potentially carcinogenic compounds, especially if the assay is done in liquid suspension and if more than 1 pair of tester strains is used. Advantages and disadvantages of the assay are discussed and suggestions are made for improvements in the system.

Animals↗