Are Isocitrate Lyase and Phosphoenolpyruvate Carboxykinase Involved in Gluconeogenesis during Senescence of Barley Leaves and Cucumber Cotyledons?

Chen, Zhihui; Walker, Robert P.; Acheson, Richard M.; Técsi, László I.; Wingler, Astrid; Lea, Peter J.; Leegood, Richard C.

doi:10.1093/pcp/pcd021

Cited by 58 publications

(34 citation statements)

References 39 publications

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“…The amino acid profile in exudates is similar to that from other species. This is consistent with a previous proposal that EFP may be specialized for delivering amino acids, based on immunolocalization of enzymes involved in nitrogen export (41).…”

Section: Discussionsupporting

confidence: 93%

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Zhang

Tolstikov

Turnbull

et al. 2010

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

133

131

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Cucurbitaceous plants (cucurbits) have long been preferred models for studying phloem physiology. However, these species are unusual in that they possess two different phloem systems, one within the main vascular bundles [fascicular phloem (FP)] and another peripheral to the vascular bundles and scattered through stem and petiole cortex tissues [extrafascicular phloem (EFP)]. We have revisited the assumption that the sap released after shoot incision originates from the FP, and also investigated the long-standing question of why the sugar content of this sap is ∼30-fold less than predicted for requirements of photosynthate delivery. Video microscopy and phloem labeling experiments unexpectedly reveal that FP very quickly becomes blocked upon cutting, whereas the extrafascicular phloem bleeds for extended periods. Thus, all cucurbit phloem sap studies to date have reported metabolite, protein, and RNA composition and transport in the relatively minor extrafascicular sieve tubes. Using tissue dissection and direct sampling of sieve tube contents, we show that FP in fact does contain up to 1 M sugars, in contrast to low-millimolar levels in the EFP. Moreover, major phloem proteins in sieve tubes of FP differ from those that predominate in the extrafascicular sap, and include several previously uncharacterized proteins with little or no homology to databases. The overall compositional differences of the two phloem systems strongly indicate functional isolation. On this basis, we propose that the fascicular phloem is largely responsible for sugar transport, whereas the extrafascicular phloem may function in signaling, defense, and transport of other metabolites.cucurbitaceae | symplastic loading | extrafascicular | exudate | P-protein

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Section: Discussionsupporting

confidence: 93%

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Zhang

Tolstikov

Turnbull

et al. 2010

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

133

131

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“…Thus it is strongly increased by asparagine . PEPCK may also be involved in the transport of nitrogenous assimilates out of senescing cucumber cotyledons (Chen et al 2000). Similarly, in kinetoplastids (e.g.…”

Section: Introductionmentioning

confidence: 99%

Phosphoenolpyruvate carboxykinase in cucumber plants is increased both by ammonium and by acidification, and is present in the phloem

Chen

Walker

Técsi³

et al. 2004

Planta

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In cucumber ( Cucumis sativus L.), phosphoenolpyruvate carboxykinase (PEPCK) was shown by activity measurements and immunoblots to be present in leaves, stems, roots, flowers, fruit and seed. However, immunolocalisation showed that it was present only in certain cell types. PEPCK was present in the companion cells of the adaxial phloem of minor veins, the adaxial and abaxial phloem of larger veins, the internal and external phloem of vascular bundles in petioles and stems, the phloem in roots and the extra-fascicular phloem in leaves, cotyledons, petioles and stems. Immunohistochemical evidence suggests that both the extra-fascicular phloem and the adaxial phloem are involved in the transport of amino acids. In roots and stems, the abundance of PEPCK was greatly increased by watering plants with a solution of ammonium chloride at low, but not at high pH. PEPCK also increased in leaves, but not roots or stems, of seedlings grown in an atmosphere containing 5% CO(2), and in roots and stems of seedlings watered with butyric acid. All these treatments are known to lower the pH of plant cells. Amino acid metabolism in the phloem may produce an excess of carbon skeletons, pH perturbations and an imbalance in the production/utilisation of NADH. This raises the possibility that PEPCK may function in the conversion of these carbon skeletons to PEP, which, depending on the energy requirements of the phloem, is subsequently utilised by either gluconeogenesis or the Krebs cycle, which both consume protons.

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“…However, a different mechanism was proposed for ICL and PEPCK enzyme involvement in senescing organs that also needs to be elucidated in the future [1].…”

Section: Discussionmentioning

confidence: 99%

Metabolic Gene Expression in Lipid Metabolism during Cotyledon Development in Cucumbers and the Possibility of a Secondary Transport Route of Acetyl Units

Jeong¹,

Kim

2014

Journal of Life Science

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We investigated the expression of cucumber genes involved in lipid mobilization and metabolism during cotyledon development to compare gene activity and to study the direction of carbon (acetyl unit) transport between glyoxysomes and mitochondria. The core metabolic pathway involving 10 genes was examined in four intracellular compartments: glyoxysomes (peroxisomes), mitochondria, chloroplasts, and cytosol. Additionally, we tested the early germination response of dark-grown seedlings and the immediate light response for a further 3 days. According to the reverse transcription polymerase chain reaction (RT-PCR), 3-L-ketoacyl-CoA thiolase 2 (Thio2), isocitrate lyase (ICL), and malate synthase (MS), the genes involved in storage lipid mobilization showed a similar and consistent pattern of gene expression in seedling development. Furthermore, coordinate expression of the A BOUT DE SOUFFLE (BOU) gene with ICL and MS during seedling emergence pointed to a possible secondary route of acetyl unit (acetyl-CoA) transport between peroxisomes and mitochondria in cucumber. The expression of the BOU gene was light dependent, as shown by BOU activity in Arabidopsis, suggesting that the dark condition also results in weak membrane biogenesis. In addition, several genes were active throughout the development of the green cotyledon, even during senescence. In conclusion, this study summarizes oil-seed germination and gene expression during cucumber cotyledon development and proposes an additional route for acetyl unit transport.

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Are Isocitrate Lyase and Phosphoenolpyruvate Carboxykinase Involved in Gluconeogenesis during Senescence of Barley Leaves and Cucumber Cotyledons?

Cited by 58 publications

References 39 publications

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Phosphoenolpyruvate carboxykinase in cucumber plants is increased both by ammonium and by acidification, and is present in the phloem

Metabolic Gene Expression in Lipid Metabolism during Cotyledon Development in Cucumbers and the Possibility of a Secondary Transport Route of Acetyl Units

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