Search PubMed⌕ Search

Biomedical subjects

R Barr

Publications and source records attributed to R Barr.

119 records · Page 7Linked to original sources
PubMed1969

The Occurence of delta-Tocopherylquinone in Higher Plants and Its Relation to Senescence.

delta-Tocopherylquinone (deltaTQ) content was determined in tobacco and yellow maple leaves, green ivy leaves and cactus tissues. It was found that the concentration of delta-TQ was highest in mature or senescent tissues, such as white tobacco leaves (0.02 mumole/g dry wt) while its detection was uncertain in young, green leaves from the apex of tobacco plants. Fractionation by centrifugation of senescent tobacco leaves showed that the osmiophilic globule fraction was enriched in delta-TQ. Electron microscope studies of young, mature and senescent tobacco tissues showed progressive changes in the size and number of osmiophilic globules. After chloroplast breakdown in senescent tobacco leaves, these globules became the predominant constituents of the organelle. delta-TQ which is associated with osmiophilic globules may play a role in the development of plants, particularly during senescence.

Journal Article↗
PubMed1968

Comparative Studies on Plastoquinones. IV. Plastoquinones in Algae.

Plastoquinones A and C have been found in all classes of algae, including representatives of greens, yellow-greens, blue-greens, reds, browns and the flagellate, Euglena. Plastoquinone C from red and brown algae can be separated into 6 different types. An additional plastoquinone C has been found in Gigartina and Rhydomela. From chromatographic evidence this may be equivalent to plastoquinone C(o), a C type with a hydroxyl group on the first isoprene unit of the terpenoid sidechain of this substituted benzo-quinone. The ubiquinone, vitamin K and alpha-tocopherylquinone content of several algae is also reported. The presence of plastoquinone A in all green plants and many algae indicates that it may be a functional element in photosynthesis. Our study shows that plastoquinone C is more regularly present in algae than has been previously shown.

Journal Article↗
PubMed1967

Comparative Studies on Plastoquinone II. Analysis for Plastoquinones A, B, C, and D.

Two different methods for the extraction and assay of plastoquinones A, B, C and D from chloroplasts of green plants have been described. The long procedure involves separation of aqueous and lipid phases of extract in a separatory funnel, column chromatography, purification on thin-layer plates, and spectrophotometric assays for quantitative determination of the various plastoquinones. The short procedure is based on spotting lipid extracts from chloroplasts on thin layer plates and comparing leucomethylene blue spots of unknown quinones with a series of spots produced by known amounts of the 4 standard plastoquinones on the same plate.Reliability of the 2 procedures is shown by presenting recovery data (82% recovery for PQ A by the long method and 64-100% recovery by the short method). Various solvent systems for quinone purification are described. Separation of plastoquinones B and C into 6 components each is demonstrated for spinach and a tomato mutant, high pigment (hp). Plastoquinone C is shown to be equivalent to C(1)-C(4) while D corresponds to PQ C(5) and C(6) according to Griffiths, Wallwork and Pennock's designation. The term PQ D is therefore redundant and should be abandoned in favor of specific designation of PQ C type.

Journal Article↗
PubMed1967

Comparative Studies on Plastoquinones. III. Distribution of Plastoquinones in Higher Plants.

The distribution of plastoquinones A 45, B and C was studied in representatives from 34 different plant families beginning with liverworts and mosses to higher plants. All of these species, including many monocots and dicots, contained significant amounts of the 3 quinones. Two species of Aesculus contained plastoquinone A 20 in addition to plastoquinone A 45, B, and C. Many dicots, such as Aesculus, watermelon, tobacco and tomato accumulated increasing quantities of plastoquinones A and C(1)-C(4) during the growing season. The concentrations of plastoquinones B and C(5)-C(6) tended to remain at a constant low level during the season (<0.01 mumole per mg chlorophyll). Preliminary studies with bean plants (Vicia faba and Phaseolus sp.) indicate that the levels of quinones varied little under different growth conditions (day length and temp.) although Vicia faba tended to have higher PQ A values with increased temperature.

Journal Article↗
PubMed1966

Human trichinosis: report of four cases, with emphasis on central nervous system involvement, and a survey of 500 consecutive autopsies at the Ottawa Civic Hospital.

In 1963, acute trichinosis was recognized in four patients at the Ottawa Civic Hospital. One presented with cavernous sinus thrombosis and sixth nerve palsy. A second had a severe systemic infection with myocarditis; the signs of myocarditis appeared in the third week. Electrocardiographic abnormalities included T-wave flattening, prolongation of PR interval and QRS complex, and non-specific changes in 25%. Central nervous system involvement occurred in the second week with general symptoms (headache, delirium and psychotic behaviour), followed in the third week by focal signs (nerve palsy, convulsion, pareses and coma).The incidence of trichinosis in the U.S.A. fell from 15.9% before 1948 to 4.5% in the period 1948-1963. The Canadian incidence in the period from 1940 to 1943 was 5.6%. In a survey in Ottawa using the Baermann digestion and compression methods, four positive cases were found out of 500 diaphragms examined. These figures indicate the success of the public health regulations aimed at controlling trichinosis. A gastrocnemius muscle biopsy is still an invaluable diagnostic tool, especially in critically ill patients with negative skin tests and no eosinophilia.

Adrenocorticotropic Hormone↗
PubMed1966

Plastoquinone B.

A compound found in spinach and other higher plants previously referred to as R 263 has now been found to be a breakdown product of plastoquinone B. This quinone, PQ B, is found with 8 other quinones in spinach chloroplasts. These 9 quinones are PQ A, PQ B, PQ C, PQ D (7, 8, 15) Vitamin K(1) (10, 12), an unknown naphthoquinone (13) and alpha-, beta- and gamma-tocopherylquinones (7, 12). An improved method for purification of plastoquinone B is described. Previous confusion of this compound with other quinoid material on silica gel is described and corrected R(F) values are given. The activity of PQ B is similar to the activity of PQ C in restoration studies of the photo-reduction of ferricyanide and indophenol.

Journal Article↗
PubMedDate not supplied

Developmental changes in imitation from television during infancy.

Infants' (N = 276) ability to learn from television under seminaturalistic conditions was examined in five experiments with 12-, 15-, and 18-month-olds. In all experiments, an adult performed a series of specific actions with novel stimuli. Some infants watched the demonstration live, and some infants watched the same demonstration on television from prerecorded videotape. Infants' ability to reproduce the target actions was then assessed either immediately or after a 24-hour delay. Infants of all ages exhibited imitation when the actions were modeled live. There were age-related and task-related differences, however, in infants' ability to imitate the same actions modeled on television. The role of perceptual, attentional, and cognitive development in the ability to learn from television is discussed.

Child Development↗