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R P Poincelot

Publications and source records attributed to R P Poincelot.

18 recordsLinked to original sources
PubMed1977

Isolation of envelope membranes from bundle sheath chloroplasts of maize.

Bundle sheath strands were isolated from maize (Zea mays L.) leaves treated with preparations of cellulase, hemicellulase, and pectinase. A three-phase discontinuous gradient yielded two fractions of envelope membranes from bundle sheath chloroplasts. Buoyant densities were 1.06 and 1.09 g cm(-3). The lighter fraction contained membrane vesicles under light microscopy, but centrifugation produced a pellet that was too small and unstable for purposes of electron microscopy. The heavier fraction contained single and double membrane vesicles and was studied further. Enzymic, chemical, light microscopic, and electron microscopic examination showed less than 2% contamination by stromal contents, no contamination by microbial, microsomal, or mitochondrial membranes, and possible low levels of lamellar membrane contamination. Yields of 0.5 mg of envelope membrane protein were obtained from 56-g leaf sections. The Mg(2+)-dependent nonlatent ATPase activity, a marker enzyme for chloroplast envelope membranes, was 40 mumoles Pi released hr(-1) mg protein(-1), a value similar to that obtained with pure mesophyll chloroplast envelope membranes from other plants.

Journal Article↗
PubMed1976

Isolation and bicarbonate transport of chloroplast envelope membranes from species of differing net photosynthetic efficiency.

A three-phase discontinuous sucrose gradient yielded two fractions of chloroplast envelope membranes from spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L., mesophyll and undifferentiated chloroplasts). These species were selected to represent plants with fast photorespiration and slow net photosynthesis, fast photorespiration yet fast net photosynthesis, and slow photorespiration and fast net photosynthesis, respectively. Buoyant densities were 1.08 and 1.11 g cm(-3). The light fraction contained primarily single (incomplete) membrane vesicles and the heavy fraction double (complete) ones. Enzymic, chemical, and electron microscopic examination of the complete envelope membranes showed a lack of microbial, microsomal, mitochondrial, and lamellar membrane contamination as well as stromal contamination. Envelope membranes for all species examined were found to contain 2 to 4% of the total chloroplast protein and yields of about 0.2 to 0.4 mg of protein were obtained from 40 g leaves. An Mg(2+)-dependent nonlatent ATPase, a marker enzyme for chloroplast envelope membranes, had the following activities (mumoles of phosphate released/hr(-1) mg protein(-1)): spinach, 77; sunflower, 163; old maize, 126; and young maize, 87. Bicarbonate transport was directly correlated with levels of ATPase activity in spinach and sunflower envelope membranes. Transport of HCO(3) (-) with sunflower envelope membranes approached that of young maize.

Journal Article↗
PubMed1976

Lipid and Fatty Acid composition of chloroplast envelope membranes from species with differing net photosynthesis.

Lipid and fatty acid compositions were determined for chloroplast envelope membranes isolated from spinach (Spinacia oleracea L.), sunflower (Helianthus annuus L.), and maize (Zea mays L.) leaves. The lipid composition was similar in sunflower, spinach, and undifferentiated maize chloroplast envelope membranes and different in maize mesophyll chloroplast envelope membranes. The predominant lipid constituents in all envelope membranes were monogalactosyldiglyceride (27 to 46%), digalactosyldiglyceride (18 to 33%), and phosphatidylcholine (7 to 30%). The fatty acid composition was also similar in sunflower and spinach chloroplast envelope membranes in comparison to those from maize. The major acyl fatty acids of the chloroplast envelope membrane were palmitic (C(16:0), 41 and 36%) and linolenic (C(18:3), 29 and 40%) acids for spinach and sunflower; palmitic (77%) and stearic (C(18:0), 12%) acids for young maize; and palmitic (61%), stearic (14%), and linolenic (13%) acids for mature maize. The differences in lipid and acyl fatty acid compositions among these plants which vary in their rates of net photosynthesis were largely quantitative rather than qualitative.

Journal Article↗
PubMed1975

Transport of Metabolites across Isolated Envelope Membranes of Spinach Chloroplasts.

Isolated envelope membranes of spinach chloroplasts (Spinacia oleracea L. var. Viroflay) exhibited selective permeability. Metabolites such as 3-phosphoglycerate, bicarbonate, glyoxylate, and acetate were transported rapidly; 6-phosphogluconate, glycolate, glycine, l-malate, and succinate were intermediate; whereas glucose 6-phosphate, fructose 1,6-diphosphate, and sucrose were hardly transported. Transport rates, metabolite accumulations within the membrane vesicles, and the internal water volume of isolated and in situ envelope membranes were compared and found to show similar trends.

Journal Article↗
PubMed1974

Uptake of bicarbonate ion in darkness by isolated chloroplast envelope membranes and intact chloroplasts of spinach.

Bicarbonate uptake by isolated chloroplast envelope membranes and intact chloroplasts of spinach (Spinacia oleracea L. var. Viroflay) in darkness exhibited a similar dependency upon temperature, pH, time, and concentrations of isolated or attached envelope membranes. This similarity in uptake properties demonstrates the usefulness of the envelope membranes for the study of chloroplast permeability. Maximal rates for dark HCO(3) (-) uptake by isolated envelope membranes and intact chloroplasts were more than sufficient to account for the maximal rates of photosynthetic CO(2) fixation observed with intact chloroplasts. The active species involved in the uptake process was found to be HCO(3) (-) and not CO(2). The significance of HCO(3) (-) uptake and its relationship to carbonic anhydrase and ribulose diphosphate carboxylase is discussed. Conditions for maximal HCO(3) (-) uptake in darkness by intact chloroplasts were found to be similar to those required for maximal photosynthetic CO(2) fixation, suggesting that HCO(3) (-) uptake by the envelope membrane may regulate photosynthetic CO(2) fixation.

Journal Article↗
PubMed1974

An improved method for the isolation of spinach chloroplast envelope membranes.

A three-phase, discontinuous sucrose gradient yielded two distinct fractions of envelope membranes from spinach (Spinacia oleracea L.) chloroplasts. Their buoyant densities were 1.08 g cm(-3) and 1.11 g cm(-3). Electron micrographs showed the lighter and heavier fractions to consist primarily of single and double membranes, respectively. The milligrams of lipid-milligrams of protein ratio for the complete envelope membrane (double membrane fraction) was 1.74. Thin layer chromatograms showed that the lipids of the complete envelope membranes were similar to those found in earlier preparations which consisted of single and double membranes. This isolation procedure is superior to earlier methods in that the percentage of complete envelope membranes is greater and the yield is almost three times as great. Enzymatic and chemical analyses and microscopic examination showed the complete envelope membranes were free of bacterial, fungal, microsomal, mitochondrial, and lamellar membrane contamination as well as stromal contamination. The specific activities of nonlatent Mg(2+) -dependent ATPase (80 mumoles of phosphate released hr(-1) mg protein(-1)) were about 10-fold higher than those values found with earlier preparations consisting of single and double membranes, indicating that the ATPase is largely lost in preparations containing single membranes. These higher values show that the ATPase is located in the double membrane and probably functions in the transport processes of the envelope membrane.

Journal Article↗
PubMed1973

Differences in Lipid Composition between Undifferentiated and Mature Maize Chloroplasts.

Lipid compositions of undifferentiated maize (Zea mays) chloroplasts, capable of fixing CO(2), were compared with the lipid compositions of mature chloroplasts, which do not fix CO(2), located in both the mesophyll and bundle sheath cells. The major lipids found in all three chloroplast types were the glycolipids, monogalactosyl diglyceride and digalactosyl diglyceride, followed by decreasing amounts of sulfolipid, phosphatidyl glycerol, phosphatidyl choline, phosphatidyl inositol, and diphosphatidyl glycerol. Quantitative differences in lipid components were observed among the chloroplast types. The mesophyll and bundle sheath maize chloroplasts differed in their chlorophyll a/chlorophyll b ratios (2.27 and 4.13 respectively) and their content of glycolipid relative to chlorophyll (51.8% glycolipid to 20.9% chlorophyll and 84.5% glycolipid to 10.1% chlorophyll respectively). A comparison between the lipid compositions of maize mesophyll chloroplasts and mesophyll chloroplasts obtained from spinach, sugar beet, and tobacco showed many similarities.

Journal Article↗
PubMed1972

The distribution of carbonic anhydrase and ribulose diphosphate carboxylase in maize leaves.

Extraction of maize (Zea mays) leaves by progressive grinding under suitably protective conditions yields total carbonic anhydrase activities (4800 units per milligram chlorophyll) comparable to the activity in spinach (Spinacia oleracea) leaves. The total ribulose diphosphate carboxylase activity was also equal to or greater than the best literature values for maize. Of the total leaf carbonic anhydrase, 72.5% on a chlorophyll basis was present in the mesophyll cells and 14.2% in the bundle-sheath cells. The distribution of the total leaf ribulose diphosphate carboxylase between the mesophyll and bundle-sheath cells was 42.0 and 48.7% respectively. There was three times as much total chlorophyll in extracts of the mesophyll cells compared with the bundle-sheath cells of maize. Similar results for the above distribution of the two enzymes were found using a differential grinding technique. The possible function of carbonic anhydrase in photosynthesis is discussed. The equal distribution of ribulose diphosphate carboxylase activity between the mesophyll and bundle-sheath cells casts doubt upon the hypothesis that a rigid biochemical compartmentation exists between these cell types in maize.

Journal Article↗
PubMed1972

Simple dye release assay for determining cellulolytic activity of fungi.

A colorimetric assay, based on the release of dye from a paper substrate, is described as a simple and rapid means of detecting cellulolytic activity. It is readily adaptable to rapidly screening in situ large numbers of fungal liquid cultures. Since it is a nondestructive assay, samples can be recovered for later use.

Cellulose↗