The specific radioactivity of glycolic acid in relation to the specific activity of carbon dioxide evolved in light in photosynthesizing sunflower leaves

Agrawal, Pramod K.; Fock, Heinrich P.

doi:10.1007/bf00386820

Cited by 7 publications

(1 citation statement)

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“…interm ediates, thus eliminating a parallel dilution of C label in p.c.o.c. interm ediates owing to refixation of C0 2; Jackson & Volk 1970;Ludwig & Canvin 1971 a, b ;Agrawal & Fock 1978). 180 can also be diluted by inp of PGA from the p.c.r.c.…”

Section: R E S U L T S a N D Discussionmentioning

confidence: 99%

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C

Raven

Griffiths

Glidewell

et al. 1982

Proc. R. Soc. Lond. B.

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Substantial incorporation of 18 O 2 into photorespiratory carbon oxidation cycle intermediates in illuminated Spinacia oleracea leaves confirms that oxygenase activity of the enzyme ribulose biphosphate carboxylase–oxygenase is a major source of glycollate in illuminated leaves. No 18 O 2 incorporation into oxalate was detected in these experiments, although 13 C incorporation from 13 CO 2 shows that oxalate synthesis is occurring under the experimental conditions. This result tends to minimize the role of a direct oxidation of glyoxylate derived (via phosphoglycollate and glycollate) from ribulose biphosphate oxygenase activity in oxalate synthesis in Spinacia . Measurements of δ 13 C show (in confirmation of earlier reports) that oxalate from Spinacia is less depleted in 13 C than is bulk organic C in the plant; it is possible the phosphoenolpyruvate carboxylase is involved in the production of the oxalate precursor. Of the plants tested, Mercurialis and Pelargonium shared with Spinacia the high δ 13 C value, while Chenopodium (closely related to Spinacia ), Oxalis (more distantly related to Pelargonium ) and two members of the Polygonaceae had oxalate δ 13 C values close to the whole-leaf δ 13 C value, which suggests derivation of both oxalate C atoms from carboxylase activity of the enzyme ribulose biphosphate carboxylase–oxygenase.

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Section: R E S U L T S a N D Discussionmentioning

confidence: 99%

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C

Raven

Griffiths

Glidewell

et al. 1982

Proc. R. Soc. Lond. B.

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Glyoxylate decarboxylation during photorespiration

Grodzinski

1978

Planta

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At 25° C under aerobic conditions with or without gluamate 10% of the [1-(14)C]glycollate oxidised in spinach leaf peroxisomes was released as (14)CO2. Without glutamate only 5% of the glycollate was converted to glycine, but with it over 80% of the glycollate was metabolised to glycine. CO2 release was probably not due to glycine breakdown in these preparations since glycine decarboxylase activity was not detected. Addition of either unlabelled glycine or isonicotinyl hydrazide (INH) did not reduce (14)CO2 release from either [1-(14)C]glycollate or [1-(14)C]glyoxylate. Furthermore, the amount of "available H2O2" (Grodzinski and Butt, 1976) was sufficient to account for all of the CO2 release by breakdown of glyoxylate. Peroxisomal glycollate metabolism was unaffected by light and isolated leaf chloroplasts alone did not metabolise glycollate. However, in a mixture of peroxisomes and illuminated chloroplasts the rate of glycollate decarboxylation increased three fold while glycine synthesis was reduced by 40%. Although it was not possible to measure "available H2O2" directly, the data are best explained by glyoxylate decarboxylation. Catalase reduced CO2 release and enhanced glycine synthesis. In addition, when a model system in which an active preparation of purified glucose oxidase generating H2O2 at a known rate was used to replace the chloroplasts, similar rates of (14)CO2 release and [(14)C]glycine synthesis from [1-(14)C]glycollate were measured. It is argued that in vivo glyoxylate metabolism in leaf peroxisomes is a key branch point of the glycollate pathway and that a portion of the photorespired CO2 arises during glyoxylate decarboxylation under the action of H2O2. The possibility that peroxisomal catalase exerts a peroxidative function during this process is discussed.

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Effects of Light on “Dark” Respiration**Abbreviations are as follows: AMP, adenosine monophosphate; ADP, adenosine diphosphate; ATP, adenosine triphosphate; CoA, coenzyme A; DCMU, dichlorophenyl dimethyl urea; DHAP, dihydroxyacetone phosphate; Fructose-1,6-P2, fructose-1,6-bisphosphate; glucose-6-P, glucose-6-phosphate; GOGAT, glutamate synthase, E.C. 1.4.1.13 (l-glutamate: NADP-oxidoreductase (transaminating); OAA, oxaloacetate; OPPP, oxidative pentose phosphate pathway; Pi, inorganic phosphate; PEP, phos

Graham¹

1980

Metabolism and Respiration

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The specific radioactivity of glycolic acid in relation to the specific activity of carbon dioxide evolved in light in photosynthesizing sunflower leaves

Cited by 7 publications

References 10 publications

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C

Glyoxylate decarboxylation during photorespiration

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The specific radioactivity of glycolic acid in relation to the specific activity of carbon dioxide evolved in light in photosynthesizing sunflower leaves

Cited by 7 publications

References 10 publications

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes 18 O and 13 C

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes 18 O and 13 C

Glyoxylate decarboxylation during photorespiration

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The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C

The mechanism of oxalate biosynthesis in higher plants: investigations with the stable isotopes ¹⁸ O and ¹³ C