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D J Oliver

Publications and source records attributed to D J Oliver.

63 records · Page 4Linked to original sources
PubMed1980

The effect of glyoxylate on photosynthesis and photorespiration by isolated soybean mesophyll cells.

Incubating isolated soybean leaf mesophyll cells with glyoxylate increased the rates of CO(2) fixation by as much as 150%. In order to cause this stimulation, the glyoxylate must be presented to the cells before the NaHCO(3). Significant stimulation was observed 15 seconds after beginning the glyoxylate treatment. The glyoxylate-dependent stimulation was increased by high O(2) concentrations and decreased by high CO(2) concentrations. Glyoxylate treatment resulted in a 71% inhibition in the rate of CO(2) incorporation into glycolate and glycine. Glyoxylate may be stimulating net photosynthesis solely by decreasing photorespiration or it may be increasing the amount of CO(2) fixed by both decreasing photorespiration and increasing gross photosynthesis. Ribulose bisphosphate carboxylase, when preactivated and assayed in situ, was unaffected by the glyoxylate treatment.

Journal Article↗
PubMed1979

Mechanism of decarboxylation of glycine and glycolate by isolated soybean cells.

Isolated soybean leaf mesophyll cells decarboxylated exogenously added [1-(14)C]glycolate and [1-(14)C]glycine in the dark. The rate of CO(2) release from glycine was inhibited over 90% by isonicotinic acid hydrazide and about 80% by KCN, two inhibitors of the glycine to serine plus CO(2) reaction. The release of CO(2) from glycolate was inhibited by less than 50% under the same conditions. This indicates that about 50% of the CO(2) released from glycolate occurred at a site other than the glycine to serine reaction. The sensitivity of this alternative site of CO(2) release to an inhibitor of glycolate oxidase (methyl-2-hydroxy-3-butynoate) but not an inhibitor of the glutamate:glyoxylate aminotransferase (2,3-epoxypropionate) indicates that this alternative (isonicotinic acid hydrazide insensitive) site of CO(2) release involved glyoxylate. Catalase inhibited this CO(2) release. Under the conditions used it is suggested that about half of the CO(2) released from glycolate occurred at the conversion of glycine to serine plus CO(2) while the remaining half of the CO(2) loss resulted from the direct oxidation of glyoxylate by H(2)O(2).The rate of glycine decarboxylation by the glycine to serine reaction was apparently controlled by the amount of NAD in the mitochondria. Mitochondrial electron transport inhibitors, KCN and actinomycin A, inhibited glycine decarboxylation while an uncoupler, 2,4-dinitrophenol, stimulated the reaction. Competition within the mitochondria between the enzymes of dark respiration and glycine decarboxylation for limiting NAD may force substantial amounts of the glycolate formed to be decarboxylated by the direct oxidation of glyoxylate.

Journal Article↗
PubMed1978

Inhibition of photorespiration and increase of net photosynthesis in isolated maize bundle sheath cells treated with glutamate or aspartate.

Net photosynthetic (14)CO(2) fixation by isolated maize (Zea mays) bundle sheath strands was stimulated 20 to 35% by the inclusion of l-glutamate or l-aspartate in the reaction mixture. Maximal stimulation occurred at a 7.5 mm concentration of either amino acid. Since the photosynthetic rate and the glutamate-dependent stimulation in the rate were equally sensitive to a photosynthetic electron transport inhibitor, 3-(p-chlorophenyl)-1,1-dimethylurea, it was concluded that glutamate did not stimulate CO(2) fixation by supplying needed NADPH (NADH) through glutamate dehydrogenase. Treatment of the bundle sheath strands with glutamate inhibited glycolate synthesis by 59%. Photorespiration in this tissue, measured as the O(2) inhibition of CO(2) fixation (the Warburg effect), was inhibited by treatment with glutamate. The stimulation in net photosynthetic CO(2) fixation probably results from the decrease in photorespiratory CO(2) loss. This metabolic regulation of the rate of glycolate synthesis and photorespiration observed with isolated bundle sheath strands could account for the inability to detect rapid photorespiration in the mature intact maize leaf.

Journal Article↗
PubMed1978

Effect of Glyoxylate on the Sensitivity of Net Photosynthesis to Oxygen (the Warburg Effect) in Tobacco.

The addition of glyoxylate to tobacco (Nicotiana tabacum) leaf discs inhibited glycolate synthesis and photorespiration and increased net photosynthetic (14)CO(2) fixation. This inhibition of photorespiration was investigated further by studying the effect of glyoxylate on the stimulation of photosynthesis that occurs when the atmospheric O(2) level was decreased from 21 to 3% (the Warburg effect). The Warburg effect is usually ascribed to the increased glycolate synthesis and metabolism that occurs at higher O(2) concentrations. Photosynthesis in control discs increased from 59.1 to 94.7 micromoles of CO(2) per gram fresh weight per hour (a 60% increase) when the O(2) level was lowered from 21 to 3%, while the rate for discs floated on 15 millimolar glyoxylate increased only from 82.0 to 99.7 micromoles of CO(2) per gram fresh weight per hour (a 22% increase). The decrease in the O(2) sensitivity of photosynthesis in the presence of glyoxylate was explained by changes in the rate of glycolate synthesis under the same conditions.The rate of metabolism of the added glyoxylate by tobacco leaf discs was about 1.35 micromoles per gram fresh weight per hour and was not dependent on the O(2) concentration in the atmosphere. This rate of metabolism is about 10% the amount of stimulation in the rate of CO(2) fixation caused by the glyoxylate treatment on a molar carbon basis. Glyoxylate (10 millimolar) had no effect on the carboxylase/oxygenase activity of isolated ribulose diphosphate carboxylase. Although the biochemical mechanism by which glyoxylate inhibits glycolate synthesis and photorespiration and thereby decreases the Warburg effect is still uncertain, these results show that cellular metabolites can regulate the extent of the Warburg effect.

Journal Article↗
PubMed1978

Combined methenamine-silver nitrate and hematoxylin & eosin stain for fungi in tissues.

Initial examination of hematoxylin & eosin-stained tissue from a human brain specimen did not reveal the fungi which were seen in subsequent tissue sections stained with methenamine-silver nitrate. Microabscesses seen in the hematoxylin & eosin-stained sections were not apparent in the methenamine--silver nitrate-stained tissue. Staining with methenamine--silver nitrate and counterstaining with hematoxylin & eosin proved excellent not only for detecting fungus cells, but also for revealing their relationship to the host cellular response in this case and in examples of experimental murine coccidioidomycosis and histoplasmosis.

Animals↗
PubMed1977

Increasing photosynthesis by inhibiting photorespiration with glyoxylate.

Glyoxylate treatment doubles net photosynthetic carbon dioxide fixation by tobacco leaf disks because inhibition of glycolate synthesis by glyoxylate results in decreased photorespiration. These observations show that photorespiration can be metabolically regulated and suggest that genetic or chemical alteration of pool sizes of certain metabolites can produce plants with increased photosynthesis.

Glycolates↗
PubMed1977

Metabolic regulation of glycolate synthesis, photorespiration, and net photosynthesis in tobacco by L-glutamate.

Experiments were undertaken to identify and characterize control mechanisms in tobacco leaf tissue which decrease the relative contribution of photorespiratory CO(2) release and thereby increase net photosynthetic CO(2) fixation. A number of metabolites were supplied to illuminated leaf discs and their effect on the inhibition of glycolate synthesis was measured. Glycolate accumulation, in the presence of alpha-hydroxy-2-pyridinemethanesulfonic acid, was inhibited in leaf discs previously floated on 30 mM solutions of either L-glutamate, L-aspartate, phospho-enolpyruvate, or glyoxylate. The effect of glutamate on glycolate synthesis, which was investigated in detail, was concentration- and time-dependent. Glycolate synthesis was inhibited about 40% by treating leaf discs with 30 mM glutamate, and the inhibition continued for more than 4 hours after the glutamate solution was removed.The glutamate inhibition of glycolate synthesis was accompanied by a marked decrease in the rate of photorespiratory CO(2) release and by maximal increases of about 25% in net photosynthetic CO(2) fixation. The products of (14)CO(2) fixation in leaf discs previously treated with glutamate showed a decrease in glycine (26%), serine (12%), and the stronger acids (18%), and an increase in the neutral compounds (26%) in comparison with discs floated only on water.Data are presented which question whether a catabolite of glutamate or the amino acid itself is responsible for the results observed. These experiments support the view that a genetic selection strategy based on the metabolic control of photorespiration would result in large increases in net photosynthetic CO(2) assimilation in species with high rates of photorespiration.

Journal Article↗
PubMed1974

A simple carbon dioxide injection system for photosynthetic studies.

A simple carbon dioxide injection system has been developed for the maintenance of CO(2) concentrations in semiclosed cuvette systems suitable for photosynthesis and gaseous pollutant studies. The device injects small volumes of pure carbon dioxide into the cuvette in response to a signal from an infrared gas analyzer.

Journal Article↗