Search PubMed⌕ Search

Biomedical subjects

R G Bidwell

Publications and source records attributed to R G Bidwell.

12 recordsLinked to original sources
PubMed1989

Mechanism of Photosynthetic Carbon Dioxide Uptake by the Red Macroalga, Chondrus crispus.

The aim of this study was to determine how Chondrus crispus, a marine red macroalga, acquires the inorganic carbon (C(i)) it utilizes for photosynthetic carbon fixation. Analyses of C(i) uptake were done using silicone oil centrifugation (using multicellular fragments of thallus), infrared gas analysis, and gas chromatography. Inhibitors of carbonic anhydrase (CA), the band 3 anion exchange protein and Na(+)/K(+) exchange were used in the study. It was found that: (a) C. crispus does not accumulate C(i) internally above the concentration attainable by diffusion; (b) the initial C(i) fixtion rate of C. crispus fragments saturates at approximately 3 to 4 millimolar C(i); (c) CA is involved in carbon uptake; its involvement is greatest at high HCO(3) (-) and low CO(2) concentration, suggesting its participation in the dehydration of HCO(3) (-) to CO(2); (d) C. crispus has an intermediate C(i) compensation point; and (e) no evidence of any active or facilitated mechanism for the transport of HCO(3) (-) was detected. These data support the view that photosynthetic C(i) uptake does not involve active transport. Rather, CO(2), derived from HCO(3) (-) catalyzed by external CA, passively diffuses across the plasma membrane of C. crispus. Intracellular CA also enhances the fixation of carbon in C. crispus.

Journal Article↗
PubMed1987

Carbonic Anhydrase-Dependent Inorganic Carbon Uptake by the Red Macroalga, Chondrus crispus.

The rate of photosynthetic carbon uptake of Chondrus crispus Stack-house plants, at various CO(2) concentrations and pretreated with carbonic anhydrase (CA) inhibitors, was determined using an air-suspension, differential infra-red gas analyzer technique. It was found that the CA inhibitors, acetazolamide, dextran-bound acetazolamide (DBI, which does not permeate cell membranes), and subtilisin (a protease that attacks the cell surface) inhibit photosynthetic carbon uptake in C. crispus. Inhibition was greatest at low CO(2) concentrations, and decreased at CO(2) saturation. Acetazolamide inhibited carbon uptake to a greater extent than DBI. The data support the conclusion that C. crispus plants utilize HCO(3) (-) for photosynthesis, and that both cell-surface and internal CA are involved in the photosynthetic uptake of inorganic carbon.

Journal Article↗
PubMed1977

Phosphoserine and phosphohydroxypyruvic Acid: evidence for their role as early intermediates in photosynthesis.

Photosynthetic fixation of (14)CO(2) in the bean Phaseolus vulgaris, cv. Pencil Pod Black Wax, resulted in the appearance of labeled compounds that were characterized as phosphoserine and phosphohydroxypyruvate by chromatographic separation and by the synthesis of chemical derivatives. In (14)CO(2)/(12)CO(2) pulse-chase experiments these metabolites demonstrated the rapid pool saturation and depletion of (14)C characteristic of early intermediates in photosynthetic carbon fixation. They were present in sufficient amounts to account for about 35% of total carbon fixed in 1 minute.

Journal Article↗
PubMed1971

The Effect of pH on the Products of Photosynthesis in CO(2) by Chloroplast Preparations from Acetabularia mediterranea.

The effect of pH on the pathways of carbon in photosynthesis was examined in chloroplast preparations from Acetabularia mediterranea. The flow of carbon into a number of photosynthetic intermediates, particularly sucrose, glycine, serine, glycolate, and the insoluble fraction, was strongly influenced by pH. At higher pH a much larger portion of the (14)C entered intermediates of the glycolate pathway. Although maximal apparent photosynthesis occurred at pH 7.6 to 7.7, cytoplasmic pH was found to be 8.0 to 8.4, using indicators. The pattern of distribution of (14)C in intermediates of whole cells was closest to that in chloroplasts at the higher pH range.

Journal Article↗
PubMed1970

Intermediates of photosynthesis in Acetabularia mediterranie chloroplasts.

The chloroplast fraction isolated from Acetabularia mediterranie was exposed to (14)CO(2) as NaH(14)CO(3) in light and darkness, and soluble radioactive compounds were analyzed at frequent intervals. The behavior of Calvin cycle intermediates indicates that this cycle was responsible for much of the carbon fixation in the chloroplasts. However, a substantial part of recently fixed carbon was metabolized via glycolic and glyceric acids. Possible pathways for their metabolism are discussed. Some carboxylation of C(3) acids was suggested by the behavior of phosphoenolpyruvate and malate. A number of amino acids were formed. Small amounts of such compounds as citrate, succinate, and fumarate not usually associated with photosynthesis might have been derived from a low level of mitochondrial contamination. About one-third of the carbon fixed in light was present in acid-labile insoluble compounds other than polysaccharides or proteins. Dark fixation of CO(2) was very small compared with photosynthesis.

Autoradiography↗
PubMed1969

Photosynthesis, Photorespiration and Respiration of Chloroplasts From Acetabularia mediterrania.

A chloroplast fraction isolated from Acetabularia mediterrania carries on photosynthesis at rates essentially equal to those of whole cells. Electron and phase contrast microscopy reveals that the chloroplasts are intact and well preserved. Preparations contain no identifiable peroxisomes, but some cytoplasmic and mitochondrial contamination is present. Photosynthesis and CO(2) production in light by chloroplast preparations are in many respects similar to that of bean leaves, although the measured rates are somewhat lower. Respiration and photosynthesis of chloroplast preparations and whole cells of Acetabularia is essentially similar except that cells have a strong dark-type respiration which continues in light and is CO(2) dependent, the substrate being mainly recent photosynthate. The data suggest that chloroplasts are the site of photorespiration.

Journal Article↗
PubMed1969

Carbon Dioxide Exchanges in Leaves. I. Discrimination Between CO(2) and CO(2) in Photosynthesis.

In order to measure CO(2) exchange reactions by leaves using isotopes of CO(2), it is necessary to know precisely the discrimination against (14)CO(2) by leaves. Earlier determinations of discrimination are at variance, and may be inaccurate because of assumptions made about the rate of photorespiration. Maize leaves evolve little or no CO(2) in light, and so provide suitable material for this measurement. Discrimination against (14)CO(2) in photosynthesis by maize leaves is almost precisely the same as in CO(2) absorption by NaOH solution, amounting to 2.1 and 2.0% respectively. The agreement between these values and their close approximation to the relative rates of diffusion of (12)CO(2) and (14)CO(2), calculated from Graham's law, shows that diffusion into the leaf is primarily responsible for discrimination against (14)CO(2) in photosynthesis.

Journal Article↗
PubMed1968

Photorespiration.

Explore the source record for details and available documents.

Carbon Dioxide↗
PubMed1966

Effect of Growth Regulators on CO(2) Assimilation in Leaves, and its Correlation with the Bud Break Response in Photosynthesis.

Experiments have been done to confirm the previously reported effect of indoleacetic acid (IAA) on the rate of CO(2) assimilation in bean leaves. It was shown that spraying the leaves of a variety of plants caused an increase in the rate of CO(2) assimilation from 30% to 100% during the half-hour to 1 hour period following spraying. The only plant tested which did not show such an effect was corn.The breaking of dormancy of axial buds in the bean plant was correlated with an increase in the rate of CO(2) assimilation in adjacent leaves for a brief period of time. It has been shown that IAA solution sprayed on 1 leaflet of a leaf can cause an increase in the rate of CO(2) assimilation in the other leaflets, and that IAA applied to the cut stem of a leaflet or a developing bud can be transported to adjacent leaves and cause an increase in the CO(2) assimilation rate. The reaction caused by IAA is very similar to that caused by the breaking of dormancy of a bud. This indicates that the bud break response in CO(2) assimilation in leaves is caused by auxin synthesized in a bud as it begins to grow, and exported into adjacent leaves.

Journal Article↗