Prospects for increasing photosynthesis by control of photorespiration

Keys, A. J.

doi:10.1002/ps.2780140313

Cited by 10 publications

(7 citation statements)

References 23 publications

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“…Proposed useful functions of glycolate metabolism include the recycling of the carbon products of RuBP oxygenase, the production ofuseful metabolites, and protection against photooxidation (20). The present data show that AOA and AAN can severely reduce the recycling of carbon through the glycine route in A. cylindrica.…”

mentioning

confidence: 62%

Effects of Aminooxyacetate and Aminoacetonitrile on Glycolate and Ammonia Release by the Cyanobacterium Anabaena cylindrica

Bergman¹,

Renström²,

Hällbom³

et al. 1985

Plant Physiol.

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Aminooxyacetate and aminoacetonitrile cause increased excretion of glycolate by the cyanobacterium Anabaena cylindrica. Both compounds also reduce NH4-N release induced by methionine sulfoximine in nonnitrogen-fixing cultures. Changes in amino acid pool sizes together with changes in activities of some enzymes related to glycolate metabolism show that glyoxylate to glycine conversion and glycine to serine conversion are inhibited by aminooxyacetate and aminoacetonitrile, respectively. The results also verify that photorespiratory glycolate metabolism via amination of glyoxylate is operative in A. cylindrica.We have recently reported on the stimulation of glycolate excretion by INH2 in cultures of the cyanobacterium Anabaena cylindrica (4). INH inhibits the conversion of glycine to serine in the glycolate pathway of higher plants and eukaryotic algae (27). Evidence has also been presented for the photorespiratory production of ammonia by A. cylindrica (3). As with some green algae (13,23) Medium and Cultivation. Cells were grown in pure culture in either NH4Cl-supplemented (N+) or N-free (N-) BG 11 medium (26) and sparged continuously with sterile air. Cultivation and cell harvesting from N+ and N-media were carried out as detailed earlier (1, 3, 4). The N+-grown cultures were used in experiments on the release of ammonium and amino acid pool sizes, while N-grown cells were used in the remainder of the experiments. Solutions ofall inhibitors were adjusted to pH 7.5 before addition to the medium.Glycolate Excretion. The procedure given earlier (4) was used and excreted glycolate assayed according to Calkins (6). The cultures were grown on air before use and then sparged with 100% 02 from the beginning of the excretion experiments. A photon fluence rate of 200 Mumol. m2 . s' at the surface of the vessels was used during excretion assays, provided by white fluorescent tubes.Release of NH4-N. MSX (0.2 mM)-induced release of NH4-N to the medium was determined as detailed earlier (3), using the phenol hypochlorite method of Chaney and Marbach (7). Cultures were pretreated only with AOA, AAN, and INH as they all, as such, interfere with the colorimetric assay by producing a blue color similar to that of indophenol blue. Cells were centrifuged after exposure to the inhibitors, carefully washed, and resuspended in fresh N-free medium containing 0.2 mM MSX (time zero). The release of NH4-N to the medium was then determined at the time intervals given in Tables III and IV

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confidence: 62%

Effects of Aminooxyacetate and Aminoacetonitrile on Glycolate and Ammonia Release by the Cyanobacterium Anabaena cylindrica

Bergman¹,

Renström²,

Hällbom³

et al. 1985

Plant Physiol.

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“…5, inhibition of photorespiration is expected to annul glycine formation from glycollate. This supposition was con®rmed by the illumination of leaves from ggs28 at low O 2 , which also suppresses photorespiration (Keys 1983): under these conditions, the light-induced increases in the glycine and GSH pools were largely abolished and foliar c-EC content remained much higher than in leaves illuminated at 20% O 2 (Table 6). Lastly, in addition to the data shown here, supplying exogenous glycine to darkened leaves and leaf discs from ggs28 was able to prevent or reverse c-EC accumulation, while allowing GSH to remain at levels measured in illuminated leaves .…”

Section: Discussionmentioning

confidence: 91%

“…4, Table 6), glycine supply may be insucient to support maximum rates of GSH synthesis, leading to accumulation of c-EC. The possible adaptive signi®-cance of the apparently wasteful process of photorespiration has been much discussed (Keys 1983;Ogren 1984). It has been argued that supply of amino acids for biosyntheses cannot be a possible function of photorespiration, as removal of amino acids from the photorespiratory cycle would drain the Calvin cycle of carbon and lead to inhibition of CO 2 ®xation (Ogren 1984).…”

Section: Discussionmentioning

confidence: 99%

Light-dependent modulation of foliar glutathione synthesis and associated amino acid metabolism in poplar overexpressing γ-glutamylcysteine synthetase

Noctor¹,

Arisi

Jouanin

et al. 1997

Planta

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Glutathione (GSH), c-glutamylcysteine (c-EC) and major free amino acids were measured in darkened and illuminated leaves from untransformed poplars (Populus tremula´P. alba) and poplars expressing Escherichia coli genes for c-glutamylcysteine synthetase (c-ECS; EC 3.2.3.3) and glutathione reductase (GR; EC 1.6.4.2). In poplars overexpressing c-ECS, foliar c-EC contents and GSH contents were markedly enhanced compared to poplars lacking the bacterial gene for the enzyme. However, the quantitative relationship between the foliar pools of c-EC and GSH in these transformants was markedly dependent on light. In the dark, GSH content was relatively low and c-EC content high, the latter being higher than the foliar GSH contents of untransformed poplars in all conditions. Hence, this transformation appears to elevate c-EC from the ranks of a trace metabolite to one of major quantitative importance. On illumination, however, c-EC content decreased fourfold whereas GSH content doubled. Glutathione was also higher in the light in untransformed poplars and in those overexpressing GR. In these plants, c-EC was negligible in the light but increased in the dark. Cysteine content was little aected by light in any of the poplar types. No light-dependent changes in the extractable activities of c-ECS, glutathione synthetase (EC 3.2.3.2) or GR were observed. In contrast, both the activation state and the maximum extractable activity of nitrate reductase (EC 1.6.6.1) were increased by illumination. In all poplar types, glutamate and aspartate were the major amino acids. The most marked light-induced increases in individual amino acids were observed in the glutamine, asparagine, serine and glycine pools. Illumination of leaves from poplars overexpressing c-ECS at elevated CO 2 or low O 2 largely abolished the inverse light-dependent changes in c-EC and GSH. Low O 2 did not aect foliar contents of cysteine or glutamate but prevented the light-induced increase in the glycine pool. It is concluded that light-dependent glycine formation through the photorespiratory pathway is required to support maximal rates of GSH synthesis, particularly under conditions where the capacity for c-EC synthesis is augmented.

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“…Since the oxygenase reaction leads to a waste of energy and carbon, and its elimination may enhance net carbon fixation by up to 50% (Keys 1983), the enzyme is an attractive target for attempts to improve photosynthetic efficiency.…”

Section: Introductionmentioning

confidence: 99%

Mutations in loop six of the large subunit of ribulose-1,5-bisphosphate carboxylase affect substrate specificity

Parry

Madgwick

Parmar

et al. 1992

Planta

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Mutagenesis in vitro of the gene encoding the large subunit of ribulose-1,5-bisphosphate carboxylase/ oxygenase (EC 4.1.1.39) from Anacystis nidulans Synechococcus PCC 6301) was used to generate novel enzymes in Escherichia coli. Residues in C-terminal loop 6 of the β/α barrel structure of the large subunit were changed. Replacement of valine 331 with alanine caused a 90% reduction in V max but did not alter the enzyme's relative specificity towards either of its gaseous substrates, CO2 and O2. However replacement of alanine 340 with glutamate decreased the enzyme's specificity for CO2 but had no significant effect on either the K m for ribulose-1,5-bisphosphate or CO2 or on V max. In contrast replacing a small cassette of residues 338-341 produced a small increase in the specificity factor.

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Prospects for increasing photosynthesis by control of photorespiration

Abstract: Photorespiration in plants is defined and discussed. The possibility of increasing crop yields by controlling photorespiration, particularly by inhibiting the initial reaction, is considered.

Cited by 10 publications

References 23 publications

Effects of Aminooxyacetate and Aminoacetonitrile on Glycolate and Ammonia Release by the Cyanobacterium Anabaena cylindrica

Effects of Aminooxyacetate and Aminoacetonitrile on Glycolate and Ammonia Release by the Cyanobacterium Anabaena cylindrica

Light-dependent modulation of foliar glutathione synthesis and associated amino acid metabolism in poplar overexpressing γ-glutamylcysteine synthetase

Mutations in loop six of the large subunit of ribulose-1,5-bisphosphate carboxylase affect substrate specificity

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