Comparison of the Effectiveness of Glycolic Acid and Glycine as Substrates for Photorespiration

Zelitch, Israel

doi:10.1104/pp.50.1.109

Cited by 54 publications

(20 citation statements)

References 25 publications

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“…This inhibitor slowed glycolate synthesis in tobacco but not in maize, again suggesting that glycolate is produced by different pathways in these species. These results explain the inhibition of photorespiration by INH in tobacco (6,35 Pyruvate is rapidly converted to PEP in maize leaves by an active PEP synthetase (10), and each of these substrates is a better precursor of glycolic acid in maize than in tobacco (Tables III and V). Perhaps the source of the glycolate in maize is glyoxylate produced by the malate synthetase reaction from malate derived from the carboxylation of PEP and its subsequent reduction.…”

Section: Thesis Discussionmentioning

confidence: 78%

“…The radioactive carbon of pyruvate-3-"C, which is probably in equilibrium with acetate-2-"C, was incorporated and mainly into glycolate-2-"C (Table III (20,21). This inhibitor slowed photorespiration in tobacco (6,35) and strongly blocked the synthesis of serine from glycine in illuminated tobacco leaf disks (35 rates of photorespiration fix "CO2 first into oxaloacetate during photosynthesis (9,14) and have high activities of phosphoenolpyruvate carboxylase (12) in comparison with species with high rates of photorespiration, such as tobacco. Therefore, PEP was added to leaf disks in the light to increase the pool size of oxaloacetate produced during assimilation in "CO2 in order to learn whether this would affect glycolate synthesis differently in maize and tobacco.…”

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confidence: 99%

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Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Zelitch¹

1973

Plant Physiol.

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After a preliminary period in light, leaf disks floated on 10 mM a-hydroxy-2-pyridinemethanesulfonic acid to inhibit glycolate oxidase accumulate glycolate at average initial rates of 67 micromoles in tobacco and 8 micromoles per gram fresh weight per hour in maize under optimal conditions in air. In the presence of "CO2, the glycolate synthesized has a high specific radioactivity in illuminated tobacco and a low one in maize. Isonicotinic acid hydrazide also inhibits glycolate oxidation and causes a slow accumulation of glycolate in maize but not in tobacco, while it inhibits glycolate synthesis in tobacco but not in maize. Radioactive carbon in acetate-2-"C and especially pyruvate-3-VC is incorporated predominantly into the C-2 of glycolate in both species, but the specific radioactivity is much greater in maize. Glyoxylate-2-"C is readily converted to glycolate-2-"C in both species. The addition of phosphoenolpyruvate stimulated glycolate formation in maize and inhibited its synthesis in tobacco, and in the presence of "CO2 the specific radioactivity in glycolate-"C was decreased greatly by the added phosphoenolpyruvate only in maize.Thus, unsymmetrically labeled glycolate is mainly synthesized from pyruvate-3-"C by a slow pathway in maize. Tobacco possesses an additional rapid pathway that produces equally labeled glycolate more directly from fixed CO2 during photosynthesis. Glycolate is believed to be the primary substrate of photorespiration, and sufficiently rapid rates of glycolate synthesis have been observed in tobacco to account for this function. Hence the high rates of photorespiration observed in tobacco leaves compared with maize result partly from differences between these species in the pathway of glycolate synthesis.The production of CO2 occurs more rapidly in many species and varieties of illuminated leaves than it does during the usual reactions of dark respiration, and the carboxyl-carbon of glycolic acid is the main source of this photorespiratory CO2 (30, 31). Rates of photorespiration are often at least 50 and more likely 100 ,Lmoles of CO2 evolved per mg of chlorophyll per hr (33). The rapid synthesis of glycolate and its oxidation to CO2, when they occur, diminish net CO2 assimilation during photosynthesis. Hence the regulation of these biochemical pathways will frequently result in large increases in plant productivity.Although glycolate is a simple two-carbon compound, there is still uncertainty about the mechanism of its biosynthesis in photosynthetic tissues. It is well established that synthesis occurs best in light, and in relatively low concentrations of CO2 and high concentrations of oxygen in the ambient atmosphere (33). (26) that glycolate was derived from a two-carbon fragment in the cycle. Shain and Gibbs (23) have recently described an isolated system that produced glycolate from "active glycolaldehyde" obtained from fructose-6-P. Their system also contained fragmented spinach chloroplasts supplemented with transketolase, ferredoxin, and NADP+, and glycolate was sy...

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Section: Thesis Discussionmentioning

confidence: 78%

mentioning

confidence: 99%

Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Zelitch¹

1973

Plant Physiol.

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“…2 (32, 33). Recent experiments comparing tissues supplied with [1-_4C]glycolate and [1-'4C]glycine suggest that the condensation of glycine to serine does not produce sufficient C02 to account for photorespiratory rates (34), and that a direct photooxidative decarboxylation of glyoxylate (Fig. 2) is more likely to be the primary source of this C02 (35).…”

Section: Glycolate Biosynthesis and Photorespirationmentioning

confidence: 99%

Plant Productivity and the Control of Photorespiration

Zelitch

1973

Proc. Natl. Acad. Sci. U.S.A.

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The Green Revolution of the last decade has seen the yield of some food crops at least doubled by genetic alterations of plant stature and the ability of plants to respond to increased fertilizer. Since only 5-10% of the dry weight of plants comes from minerals and nitrogen in the soil, it is becoming more difficult to obtain further increases in productivity by this approach. Even scientists associated with the Green Revolution believe they have reached a plateau by these methods (1). Therefore, the next large increases in productivity must come from increasing the 90-95% of the dry weight that comes from the assimilation of airborne CO2 during photosynthesis.The productivity of plants (dry weight per unit of ground area) is determined by the gross CO2 assimilation during photosynthesis minus the CO2 released during respiration. The "dark" respiration processes of green plants, which probably also occur as well in the light, are biochemically similar to those found in animal tissues and many microorganisms, and are essential for the growth and maintenance of plant cells. It is not certain whether all of the dark respiration is essential, or whether some portion of it may sometimes be uncoupled from ATP production. This wasteful portion of respiration could cause diminished productivity (2). However, it is well documented that many plant species and varieties respire away large portions of their recently fixed CO2 during illumination by an entirely different biochemical process of respiration, known as photorespiration. Since photorespiration is often much faster in terms of CO2 production than dark respiration, photorespiration greatly lowers plant productivity where this occurs. Some biochemical and plant breeding experiments will be described that hold promise for retention of much of the photorespired C02, leading to large increases in crop yields.Relation of net photosynthesis to productivity among speciesCrop species vary greatly in their yields of dry weight. For example, from statistics of average market yield in the United States (Table 1), one can calculate that the crop growth rate for maize silage, sorghum silage, and sugarcane (cane) is at least double that for spinach, tobacco (leaf plus stalk), and hay grasses (3). The higher-yielding leafy species all have low fluxes of photorespiration compared with the less efficient species. Table 2 contains typical values of CO2 assimilation taken from the literature; it shows that much faster rates are usually found in the higher-yielding tropical grasses and in some weeds, as compared with many common crop plantsincluding spinach, tobacco, and orchard grass-that are lower yielding. A large part of the differences in net photosynthesis between the efficient and nonefficient species can be explained by the much slower rate of photorespiration that is encountered naturally only in the efficient plants. Characteristics of photorespirationSince photorespiration is such an important process, it is interesting to speculate on why its discovery was so long delayed....

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“…Although HPMS has been used over a short time span to inhibit glycolate biosynthesis and increase photosynthesis (24,25), the results with the bean leaves indicated that HPMS was Plant Physiol. Vol.…”

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Variables Affecting the CO₂ Compensation Point

Smith¹,

Tolbert²,

Ku³

1976

Plant Physiol.

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Some factors influencing dark respiration, photorespiration, and photosynthesis were examined for their effect on the CO2 compensation point (70 ,Ill) of detached soybean (Glycine max) leaf discs. A higher compensation point in young leaves decreased to the constant value after leaf expansion and maturation, but increased again during senescence.The compensation point was 40 to 50% higher in plants grown in the summer than in the winter. The compensation point and dark respiration increased with temperatures above 17 C. Below 17 C dark respiration continued to decrease, but the compensation point did not decrease further. Increasing light intensities did not affect the compensation point.The effect of selected chemicals on the compensation point were surveyed. Some buffer components did not greatly alter the compensation point but organic solvents lowered it. Potassium phosphate and pyrophosphate greaty increased it. Inhibitors of photosynthesis increased the compensation point. Hydroxypyridinemethanesulfonate and sodium bisufite severely inhibited photosynthesis in soybean leaves, stimulated dark respiration, and increased the compensation point.

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Comparison of the Effectiveness of Glycolic Acid and Glycine as Substrates for Photorespiration

Cited by 54 publications

References 25 publications

Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Plant Productivity and the Control of Photorespiration

Variables Affecting the CO₂ Compensation Point

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Comparison of the Effectiveness of Glycolic Acid and Glycine as Substrates for Photorespiration

Cited by 54 publications

References 25 publications

Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Alternate Pathways of Glycolate Synthesis in Tobacco and Maize Leaves in Relation to Rates of Photorespiration

Plant Productivity and the Control of Photorespiration

Variables Affecting the CO2 Compensation Point

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Product

Resources

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Variables Affecting the CO₂ Compensation Point