Biomedical subjects

R A Kennedy

Publications and source records attributed to R A Kennedy.

At least 37 records · Page 2Linked to original sources

PubMed1989

A comparison of photoscreening techniques for amblyogenic factors in children.

We screened 236 consecutive patients aged 6 years or less using an Off-Axis photoscreener and an Otago-type photoscreener. With a masked standardized clinical assessment as the standard, an overall comparison of the results obtained with the two techniques revealed a sensitivity and specificity in the neighbourhood of 0.85 and 0.87 respectively for the Off-Axis photoscreener and 0.94 and 0.94 respectively for the Otago photoscreener. Both techniques, but especially the Off-Axis technique, were less sensitive and specific in younger children (24 months or less). Fundus colour (light or dark) did not greatly affect sensitivity or specificity. Photoscreening with the pupil dilated led to an increase in false-positive results with both techniques. Our results showed the Otago photoscreener to be superior in this clinical trial.

Amblyopia↗

PubMed1987

Activities of isolated mitochondria and mitochondrial enzymes from aerobically and anaerobically germinated barnyard grass (echinochloa) seedlings.

Activity of mitochondria isolated from whole seedlings of Echinochloa crus-galli (L.) Beauv. var oryzicola germinated under aerobic and anaerobic conditions for 5 to 7 days was investigated. Mitochondria from both treatments exhibited good respiratory control and ADP/O ratios. Although O(2) uptake was low in anaerobic mitochondria, activity rapidly increased when the seedlings were transferred to air. Mitochondria from both aerobically and anaerobically grown seedlings of E. crus-galli var oryzicola maintained up to 66% of their initial respiration rate in the presence of both cyanide and salicylhydroxamic acid, and the inhibitory effects of cyanide and azide were additive. In addition, antimycin A was not an effective inhibitor of respiration. Reduced-minus-oxidized absorption spectra revealed that cytochromes a, a(3), and b were reduced to a greater extent and cytochrome c was reduced to a lesser extent in anaerobically germinated seedlings relative to that in aerobically germinated seedlings. An absorption maximum in the cytochrome d region of the spectrum was reduced to the same extent under both germination conditions and an absorption maximum at 577 nm was present only in anaerobically germinated seedlings. Anaerobically germinated seedlings contained 70% of the cytochrome c oxidase activity found in air grown seedlings. Upon exposure to air, the developmental pattern of this enzyme in anaerobically germinated seedlings was similar to air controls. Succinate dehydrogenase activity in anaerobic seedlings was only 45% of the activity found in aerobically germinated seeds, but within 1 hour of exposure to air, the activity had increased to control levels. The results suggest that mitochondria isolated from E. crus-galli var oryzicola differ from other plants studied and that the potential for mitochondrial function during anaerobiosis exists.

Journal Article↗

PubMed1986

Developmental Changes in Photosynthetic Gas Exchange in the Polyol-Synthesizing Species, Apium graveolens L. (Celery).

Developmental changes in photosynthetic gas exchange were investigated in the mannitol synthesizing plant celery (Apium graveolens L. ;Giant Pascal'). Greenhouse-grown plants had unusually high photosynthetic rates for a C(3) plant, but consistent with field productivity data reported elsewhere for this plant. In most respects, celery exhibited typical C(3) photosynthetic characteristics; light saturation occurred at 600 micromoles photons per square meter per second, with a broad temperature optimum, peaking at 26 degrees C. At 2% O(2), photosynthesis was enhanced 15 to 25% compared to rates at 21% O(2). However, celery had low CO(2) compensation points, averaging 7 to 20 microliters per liter throughout the canopy. Conventional mechanisms for concentrating CO(2) were not detectable.

Journal Article↗

PubMed1985

Botulinum A toxin injection as a treatment for blepharospasm.

Thirty-nine patients with blepharospasm were treated with injections of botulinum A toxin into the lid and brow. The maximum number of injections in one patient was 16 over a period of 24 months. A reduction of abnormal movement occurred in all patients, lasting up to 170 days. Both the amount and the duration of effect were dose dependent. Reinjection for recurrence had effects similar to the original injection. Tearing, dry-eye symptoms, or transient ptosis occurred in 20% of injections, especially in patients who had had previous eyelid surgery.

Blepharospasm↗

PubMed1985

Photosynthetic Development of Anaerobically Grown Rice (Oryza sativa) after Exposure to Air.

During anaerobic germination, rice produces a coleoptile devoid of carotenoid and chlorophyll. Further development and greening of the shoot occur upon exposure of the seedlings to air. In this study, a comparison was made between anaerobically (N(2)) germinated rice, greened upon exposure to air, and air/dark (A/D) germinated seedlings, greened upon exposure to light. After exposure to air, N(2)-grown seedlings had a 76-hour lag before net oxygen evolution occurred compared to a 6-hour lag for A/D-grown seedlings. After 98 h of greening, N(2)-grown seedlings reached a rate of oxygen evolution equivalent to that of A/D-grown seedlings after 24 hours. Chlorophyll and carotenoid content showed a similar lag, but did not reach the level found in A/D-grown seedlings even after 124 hours of exposure to air. RuBPcase activity also lagged in N(2)-grown seedlings, ultimately reaching greater values than in the ;greened' A/D-grown seedlings. Phosphoenolpyruvate carboxylase activity was constant and low in all treatments except for a transient increase after 24 hours of greening of the N(2)-grown seedlings.

Journal Article↗

PubMed1985

Seasonal Changes in the Photosynthetic Rate in Apple Trees : A Comparison between Fruiting and Nonfruiting Trees.

Seasonal changes in photosynthesis of apple trees (Malus domestica Borkh.) were monitored to examine the effect of source-sink interactions on photosynthesis and photorespiration. Elevated photosynthetic rates were observed during two periods of the growing season and correlated with the fruiting process. The first period of increased photosynthetic rates was during the bloom period, when spur leaves on flowering shoots exhibited up to 25% higher photosynthetic rates than vegetative spur leaves on a leaf area basis. CO(2) assimilation rates were also higher in fruiting trees than nonfruiting trees during the period of rapid fruit growth from July to September. Photorespiration, dark respiration, leaf resistance, and transpiration exhibited no seasonal changes which correlated to the presence or absence of fruit. These data represent the first comprehensive examination of the effects of flowering/fruit formation on photosynthesis and photorespiration in perennial plants.

Journal Article↗

PubMed1983

Anaerobiosis in Echinochloa crus-galli (Barnyard Grass) Seedlings : Intermediary Metabolism and Ethanol Tolerance.

Tolerance to ethanol and the ability to metabolize key intermediary substrates under anaerobiosis were studied in Echinochloa crus-galli (L.) Beauv. var oryzicola seeds to further characterize the mechanisms which enable it to germinate and grow without O(2).Our results indicate that E. crus-galli var oryzicola possesses an inherently high tolerance to ethanol and is able to metabolize low levels of ethanol in the absence of O(2). Concentrations of ethanol 45-fold greater than endogenous levels did not prove toxic to germinating seeds.Five-day anaerobically grown seedlings of E. crus-galli var oryzicola metabolized added [(14)C]sucrose primarily to CO(2) and ethanol. Of the soluble compounds labeled, the phosphorylated intermediates of glycolysis and the oxidative pentose phosphate pathway predominated more under anaerobiosis than in air. In addition, organic acids and lipids were labeled from [(14)C]sucrose, the latter indicating that metabolism of carbohydrate via acetyl-CoA occurred in the absence of O(2). Lipids were also labeled when seeds were supplied with [(14)C]ethanol or [(14)C]acetate. Labeling experiments using the above compounds plus [(14)C]NaHCO(3), showed further labeling of organic acids; succinate and citrate being labeled under nitrogen, while fumarate was formed in air.The above metabolic characteristics would allow for the maintenance of an active alcoholic fermentation system which, along with high alcohol dehydrogenase activity, would continue to recycle NAD and result in continued energy production without O(2). In addition, Echinochloa's ability to metabolize carbohydrate intermediates and to synthesize lipids indicates that mechanisms exist for providing the carbon intermediates for biosynthesis, particularly membrane synthesis for growth, even in the absence of O(2).

Journal Article↗

PubMed1983

Germination of Echinochloa crus-galli (Barnyard Grass) Seeds under Anaerobic Conditions : Respiration and Response to Metabolic Inhibitors.

Echinochloa crus-galli L. Beauv., a rice-field weed, can germinate and grow for extended periods of time in an anaerobic environment. Compared to pea, which does not germinate under anaerobiosis, the evolution of CO(2) in Echinochloa and rice is lower and the peak rate of CO(2) evolution is delayed when germinated without oxygen. The plants studied also differ with respect to their respiration ratio ([CO(2)] N(2)/[CO(2)] air) and metabolism used during the early stages of germination. Echinochloa does not increase its glycolytic rate under anaerobiosis, whereas pentose phosphate pathway activity appears to increase during the first 40 to 50 hours of germination.Based on its response to metabolic inhibitors (NaF, dinitrophenol, and malonate), anaerobic metabolism in Echinochloa proceeds primarily through glycolysis, with partial operation of the tricarboxylic acid cycle and little or no oxidative phosphorylation. Also, Echinochloa is sensitive to CN during aerobic germination, whereas rice appears to be able to shift to CN-insensitive electron transport. Finally, the effectiveness of cyanide and azide on inhibiting germination of Echinochloa in N(2), but not CO, suggests that cytochrome oxidase is not used to reoxidize pyridine nucleotides in the absence of oxygen. The possible existence of an alternate electron acceptor is discussed.

Journal Article↗

PubMed1983

Development of Photosynthetic Activity following Anaerobic Germination in Rice-Mimic Grass (Echinochloa crus-galli var oryzicola).

Shoots of anaerobically germinated Echinochloa crus-galli var oryzicola are nonpigmented whether germinated in light or dark, and chlorophyll synthesis is minimal for the first 12 to 18 hours of greening after exposure to ambient conditions. When chlorophyll development is compared between greening anoxic and etiolated shoots, there is a 100-fold difference in chlorophyll levels at 8 hours, an 8-fold difference at 24 hours, but roughly equal amounts at 60 hours. The chlorophyll a/b ratio approaches 3 earlier in greening anoxic shoots than in greening etiolated shoots, relative to total chlorophyll. The long lag in chlorophyll synthesis can be shortened by giving dark-grown anoxic shoots a 24-hour midtreatment of air before light.Development of photosynthetic activity in etiolated shoots, determined by CO(2) gas exchange, (14)CO(2) uptake, and activity of carboxylating enzymes closely parallels development of chlorophylls. However, development of photosynthetic capability in greening anoxic shoots does not parallel chlorophyll development; ability to fix carbon lags behind chlorophyll synthesis. A reason for this lag is the very low activity of RuBP carboxylase during the first 36 hours of greening in anoxic shoots. The activity of phosphoenolpyruvate carboxylase is also delayed, but its kinetics more closely match those of chlorophyll development.

Journal Article↗

PubMed1982

Crassulacean Acid Metabolism in the Succulent C(4) Dicot, Portulaca oleracea L Under Natural Environmental Conditions.

Crassulacean acid metabolism (CAM) was examined under natural environmental conditions in the succulent C(4) dicot Portulaca oleracea L. Two groups of plants were monitored; one was watered daily (well watered), while the other received water once every 3 to 4 weeks to produce a psi of -8 bars (drought stressed). Gas exchange, transpiration rate, and titratable acidity were measured for 24-hour periods during the growing season. CAM activity was greatest in drought-stressed plants during late August which had 13 hour days and day/night temperatures of 35/15 degrees C. Under these conditions net CO(2) uptake occurred slowly throughout the night. Diurnal fluctuations of titratable acidity took place in both leaves and stems with amplitudes of 17 and 47 microequivalents per gram fresh weight, respectively. Transpiration data indicated greater opening of stomata during the night than the day. CAM was less pronounced in drought-stressed P. oleracea plants in July and September; neither dark CO(2) uptake nor positive carbon balance occurred during the July measurements. In contrast, well-watered plants appeared to rely on C(4) photosynthesis throughout the season, although some acid fluctuations occurred in stems of these plants during September.To determine the fate of the CO(2) assimilated at night in drought-stressed Portulaca plants, exposure to (14)CO(2) during the night followed by 9 hours of ambient air in the light. Malate was the predominant compound labeled during the night, with some citrate and aspartate. No (14)CO(2) release was detected during the following day and by midafternoon the majority of the label was found in the insoluble fraction (predominantly starch). These results substantiate our earlier work with growth-chamber-grown plants and show that limited CAM activity can occur in the succulent C(4) dicot Portulaca oleracea L. under certain natural environmental conditions.

Journal Article↗

PubMed1982

Sorbitol metabolism and sink-source interconversions in developing apple leaves.

In apple (Malus domestica Borkh.) sorbitol is the primary product of photosynthesis, the major translocated form of carbon, and a common fruit constituent and storage compound. Previous work on sorbitol metabolism has revealed a NADPH-dependent aldose 6-phosphate reductase (A6PR) in green tissues, and a NAD-dependent sorbitol dehydrogenase in nongreen tissues. Results here show a decrease in sorbitol dehydrogenase activity and an increase in A6PR activity as leaves developing in the spring undergo the transition from sink to source. Sorbitol dehydrogenase activity reached a minimum as A6PR peaked. These changes were related to increases in leaf carbohydrate levels, especially sorbitol, and to increases in rates of net photosynthesis. Studies conducted in the autumn on senescing leaves also showed changes in enzyme activites, leaf carbohydrate levels, and photosynthesis. At this time, however, sorbitol dehydrogenase increased in specific activity, whereas A6PR activity, leaf carbohydrates, and photosynthetic rates all decreased substantially. Other experiments showed differences in the ability of young and mature leaves to metabolize sorbitol and in the distribution of sorbitol enzymes in leaves at transitional developmental stages. The results suggest that sorbitol metabolism in apple is tightly controlled and may be related to mechanisms regulating partitioning or source and sink activity.

Journal Article↗

PubMed1981

Anaerobic Metabolism in Germinating Seeds of Echinochloa crus-galli (Barnyard Grass) : METABOLITE AND ENZYME STUDIES.

Echinochloa crus-galli, a problem weed in rice fields, has the rare ability to germinate and to grow in a totally oxygen-free environment. After 7 days growth in the light or dark under N(2), E. crus-galli var. oryzicola produces a 2- to 3-centimeter nonpigmented shoot.Ethanol, malate, and lactate were measured in seeds germinated under N(2) and air, and compared with changes in the activities of alcohol dehydrogenase, malate dehydrogenase, NADP-malic enzyme, and phosphoenolpyruvate carboxylase. During a 7-day time course, ethanol levels increased 661 micromoles per gram dry weight under N(2), with no increase under air. Alcohol dehydrogenase activity increased 5.5 micromoles per gram dry weight per minute in N(2) compared to 1.0 in air. Corresponding increases for lactate were 7.9 micromoles per gram dry weight under N(2) and 2.7 under air, and for malate, 5.3 micromoles per gram dry weight under N(2) and 0.4 under air.Although 85% of the ethanol produced by the seedlings was found in the external solution under N(2), the seeds still contained 90 times more ethanol under anaerobic conditions than under air. No phosphoenolpyruvate carboxykinase activity was detected and phosphoenolpyruvate carboxylase activity was 10 times less under N(2) than air. Malic enzyme activity increased 5-fold under anaerobic conditions, comparable to the change under aerobic conditions. Proposed adaptive mechanisms of flood-tolerant species to anaerobiosis are discussed.

Journal Article↗

PubMed1980

Characteristics of Crassulacean Acid Metabolism in the Succulent C(4) Dicot, Portulaca oleracea L.

Crassulacean acid metabolism (CAM) was investigated in leaves and stems of the succulent C(4) dicot Portulaca oleracea L. Diurnal acid fluctuations, CO(2) gas exchange, and leaf resistance were monitored under various photoperiod and watering regimes. No CAM activity was seen in well watered plants grown under 16-hour days. Under 8-hour days, however, well watered plants showed a CAM-like pattern of acid fluctuation with amplitudes of 102 and 90 microequivalents per gram fresh weight for leaves and stems, respectively. Similar patterns were also observed in detached leaves and defoliated stems. Leaf resistance values indicated that stomata were open during part of the dark period, but night acidification most likely resulted from refixation of respiratory CO(2). In water-stressed plants maximum acid accumulations were reduced under both long and short photoperiods. At night, these plants showed short periods of net CO(2) uptake and stomatal opening which continued all night long during preliminary studies under natural environmental conditions. Greatest acid fluctuations, in P. oleracea, with amplitudes of 128 microequivalents per gram fresh weight, were observed in water-stressed plants which had been rewatered, especially when grown under short days. No net CO(2) uptake took place, but stomata remained open throughout the night under these conditions. These results indicate that under certain conditions, such as water stress or short photoperiods, P. oleracea is capable of developing an acid metabolism with many similarities to CAM.

Journal Article↗

PubMed1979

Photosynthetic Enzyme Activities and Localization in Mollugo verticillata Populations Differing in the Levels of C(3) and C(4) Cycle Operation.

Ecotypic differences in the photosynthetic carbon metabolism of Mollugo verticillata were studied. Variations in C(3) and C(4) cycle activity are apparently due to differences in the activities of enzymes associated with each pathway. Compared to C(4) plants, the activities of C(4) pathway enzymes were generally lower in M. verticillata, with the exception of the decarboxylase enzyme, NAD malic enzyme. The combined total carboxylase enzyme activity of M. verticillata was greater than that of C(3) plants, possibly accounting for the high photosynthetic rates of this species. Unlike either C(3) or C(4) plants, ribulose bisphosphate carboxylase was present in both mesophyll and bundle sheath cell chloroplasts in M. verticillata. The localization of this enzyme in both cells in this plant, in conjunction with an efficient C(4) acid decarboxylation mechanism most likely localized in bundle sheath cell mitochondria, may account for intermediate photorespiration levels previously observed in this species.

Journal Article↗

PubMed1977

Effect of different killing techniques on early labeled photosynthetic products in c(4) plants.

The choice of leaf-killing technique was found to affect significantly the distribution of label among early labeled photosynthetic products in two C(4) plants, Portulaca oleracea and Zea mays. The major effect of these procedures was on the amount of amino acids present, particularly alanine, and the ratio of malate to aspartate. Killing Portulaca leaves in alcohol generally results in more alanine and the predominance of malate over aspartate. When the leaves are killed by immediate freezing, however, aspartate contained more radioactivity than malate, and alanine was present in much reduced amounts. The various methods also differ in the relative amounts of C(3) cycle compounds and other, secondary intermediates which were obtained.

Journal Article↗

PubMed1977

Photosynthesis in c(4) plant tissue cultures: significance of kranz anatomy to c(4) Acid metabolism in c(4) plants.

The pattern of photosynthetic carbon metabolism was determined in tissue cultures of Portulaca oleracea. Four-carbon acids are the most heavily labeled photosynthetic products during short term exposure to (14)CO(2), containing greater than 40% of the total radioactivity incorporated. Phosphoglyceric acid and sugars account for only 10% of the label after equal exposure times. Other features of the CO(2) assimilation pattern in Portulaca callus tissue include a relatively large percentage of label located in various minor products throughout the time course studied, and a greater incorporation of (14)C into sugars in tissue cultures than occurs in leaves. Ultrastructurally, the chloroplasts and cells of the callus are like those in the mesophyll cells of Portulaca leaves. The requirement for Kranz anatomy for operation of functional C(4) physiology is discussed.

Journal Article↗

PubMed1977

Photosynthesis In Elodea canadensis Michx: Four-Carbon Acid Synthesis.

Experiments to determine the early labeled photosynthetic products in Elodea canadensis show that after 2 seconds of exposure to NaH(14)CO(3), 45% of the (14)C incorporated is located in malate and aspartate. Phosphoglyceric acid and sugars account for 27% of the label during similar exposures. Equivalent amounts of organic acids and C(3) cycle products are present after 8 seconds. Four-carbon acids remain relatively unchanged throughout the first 45 seconds of exposure, while sugars increase in a linear fashion. Enzyme assays indicate that ribulose diphosphate and phosphoenolpyruvate carboxylase enzymes are present in a ratio of approximately 2:1. It appears that E. canadensis is able to synthesize significant amounts of four-carbon acids via beta-carboxylation and this may play a role in maintaining a pH favorable for carboxylation in aquatic plants.

Journal Article↗

PubMed1976

Photorespiration in c(3) and c(4) plant tissue cultures: significance of kranz anatomy to low photorespiration in c(4) plants.

Photorespiration rates in tissue cultures of a C(4) plant, Portulaca oleracea, were compared to those in tissue cultures of a C(3) plant, Streptanthus tortuosus. The C(4) plant tissue cultures have one-half to one-third the photorespiration rate of the C(3) plant tissue cultures and respond to varying O(2) concentrations in a manner typical of C(4) plants. The results suggest that the lack of detectable photorespiration in C(4) plants is not related to leaf anatomy.

Journal Article↗