Enzymes of the glycolate pathway in plants without CO 2 -photorespiration

Prior illumination in C02-free air enhances a respiration from maize (Zea mays L.) leaves different in onset and duration from the postillumination burst of photorespiration. Respiration of attached leaves during the dark-light-dark sequence of the experiment was measured by infrared gas analysis of CO2 efflux from leaves at 25 ± 1 C into CO2-free N2 containing 0.04%, 2.23%, or 40% 02, or into C02-free air in an acrylic plastic chamber. Rapid flushing at 10 1 min-' replaced air by other gas mixtures.Respiration of excised leaves was measured as outlined above except for the following changes. Leaves were excised from the plant and recut beneath air-free distilled H20 in a beaker resting on the pan of a balance. The leaf was sealed into the chamber with the cut end of the leaf suspended in the beaker so that movement of solution into the leaf could be continuously monitored. In leaf-feeding experiments, the rates of respiration and steady transpiration were first established with the leaf in distilled H20, and before illumination the H20 was quickly replaced with 50 mm solutions of metabolites or with solutions containing the inhibitors HPMS1 or CMU. After illumination the pattern of respiration caused by each metabolite was then established using the protocol developed for attached leaves. During the respiration of some compounds. the 02 concentration was altered as previously described for attached leaves.The total volume of the heat exchange unit and chamber was 8.4 liters, giving a volume to leaf area ratio of approximately 20 cm2 cm-2. Relative humidity was 50 ± 5% during the experiments. Leaves were usually illuminated for 20 min at 0.38 cal cm-2 min-' (400-700 nm) during the dark-light-dark sequence to provide energy to stimulate influx of solutions of metabolites and respiration in the subsequent dark period. To measure the response to light of CO2 efflux during the illumination, illumination was attenuated with successive layers of

Section: Methodssupporting

confidence: 78%

Postillumination Respiration of Maize in Relation to Oxygen Concentration and Glycolic Acid Metabolism

Heichel¹

1972

“…mechanical) cell isolation procedures (e.g. 23,27). Analogous results were obtained with enzymically isolated mesophyll protoplasts and bundle sheath strands of maize (22).…”

Section: Cellular Localizationmentioning

confidence: 58%

Identification of Hydroxypyruvate and Glyoxylate Reductases in Maize Leaves

Kleczkowski

Edwards²

1989

Metabolism of glyoxylate and hydroxypyruvate in photosynthesizing cells is considered to be intimately related to the operation of the glycolate pathway (known also as the oxidative photosynthetic carbon cycle or C2-cycle), which is responsible for photorespiration in plants (13). In this process, which involves metabolism of several two-and three-carbon intermediates derived from P-glycolate in chloroplasts, glyoxylate

“…P-glycolate phosphatase (EC 3.1.3.18) activity was assayed by the release of Pi from P-glycolate. Reaction vessels contained 40 mm sodium cacodylate (pH 6.3), 1 mm MgC12, 5 mM P-glycolate, and uncentrifuged extract in a total volume of 1.0 ml (30). The reactions were run for 10 min at 30 C, stopped with 10% (w/v) trichloroacetic acid, the precipitate removed by centrifugation, and the supernatant assayed for Pi (31).…”

mentioning

confidence: 99%

Photosynthetic Carbon Metabolism in Isolated Maize Bundle Sheath Strands

Chollet

Ogren

1973

Photosynthetically active bundle sheath strands capable of assimilating up to 8 micromoles C02 per milligram chlorophyll per hour have been isolated from fully expanded leaves of Zea mays L. Mesophyll cell contamination of the preparations was negligible, as evidenced by light and electron microscopy and by a high ratio of chlorophyll a to chlorophyll b in the strands. Ribose 5-phosphate markedly stimulated the rate of photosynthetic "4CO2 fixation by the isolated strands. In contrast, both pyruvate and phosphoenolpyruvate had a comparatively small stimulatory effect on bundle sheath '4CO2 fixation. plants which distinguishes them from C3 species is the presence of two major chloroplast-containing leaf cell types: the bundle sheath cells which tightly surround the vascular tissue, and the mesophyll cells which in turn surround the bundle sheath layer (24).It has been suggested that in the C, panicoid grasses such as maize, sugarcane, and crabgrass, atmospheric CO2 is initially fixed by PEP carboxylase in the mesophyll, with the resulting oxaloacetate being predominantly reduced to malate by an NADP+-specific malate dehydrogenase. The malate is transported to the bundle sheath chloroplasts and decarboxylated to pyruvate and CO, by "malic" enzyme. The CO2 is refixed by RuDP carboxylase and further metabolized through the Calvin cycle (4,7,8,16,21,32). In marked contrast to this compartmentation scheme is that recently proposed by Coombs and co-workers (6, 9, 14, 15) and supported by Laetsch and Kortschak (25). These authors propose an identical reaction sequence for C, photosynthesis, but suggest that all the enzymes for photosynthetic carbon metabolism are compartmented between the mesophyll cytoplasm or nongreen leaf cells and the mesophyll chloroplasts, relegating the bundle sheath to a mere amyloplast-like function. A third scheme of C4 photosynthesis, suggesting that photosynthetic carbon metabolism is similar in both cell types, has also been proposed (29).The purpose of our studies has been to re-examine the role of bundle sheath cells in C4 photosynthesis by using a highly purified preparation of bundle sheath strands isolated from fully expanded leaves of maize. We have previously reported on the effects of oxygen on maize bundle sheath photosynthesis (12,13). A more complete description of the photosynthetic carbon metabolism of these bundle sheath strand preparations is the subject of this report.MATERIALS AND METHODS Plant Materials. Zea mays L., var. W23/L317, seeds were germinated and grown in a soil-sand-peat moss mixture in a growth chamber with a 12-hr day at 25 C and a 12-hr night at 20 C. Light of about 2000 ft-c at the leaf surface was provided by incandescent and cool white fluorescent lamps. Only fully expanded primary and secondary leaves from 11-to 14-day-old seedlings were used. For some of the enzyme assays, crude leaf extracts from the C3 plant soybean (Gb'cine max [L.] Merrill, vars. Kent and Waseda) were also prepared. Leaf material was harvested from the youngest, fully ex...