Apoplastic degradation of ascorbate: Novel enzymes and metabolites permeating the plant cell wall

Green, M A; Fry, Stephen C.

doi:10.1080/11263500500056849

Cited by 32 publications

(27 citation statements)

References 23 publications

(32 reference statements)

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“…Detection of the auxin-dependent increase in DHA in the distal zone of roots would probably require more detailed discrimination of zones in the distal part of the root. Endogenous DHA has usually been regarded as a cell wall loosening and growth promoting factor (Lin and Varner 1991;Green and Fry 2005). We observed, however, that DHA application inhibited the elongation of the primary root and stimulated lateral root formation, i.e.…”

Section: Discussioncontrasting

confidence: 45%

Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

2007

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Ascorbate levels and redox states, as well as the activities of the enzymes of ascorbate metabolism, were analyzed in roots of tomato seedlings during the culture on a medium supplemented with auxin and compared to the control cultured on an auxin-free medium. Biochemical parameters were determined separately in the distal part of the root where the inhibitory effect of auxin on root elongation growth is observed and in the proximal half on the organ which reacts to auxin treatment with increased lateral root proliferation. ASC peroxidase activity was found to be stimulated by auxin treatment in the lateral-root forming part of the root. This effect was not observed in the distal part of the organ. On the other hand, ASC oxidase activity was raised by auxin exclusively in the distal part of the root. An inhibitory effect of auxin supplementation to the medium on ASC-reducing enzymes was observed. The dehydroascorbate reductase activity was found to be inhibited by auxin only in the proximal part, while the activity of monodehydroascorbate reductase in both, the proximal and distal parts of the root. Ascorbate content increased in roots during culture irrespective of the presence of auxin. However, auxin treatment resulted in higher DHA levels and more significant participation of DHA in the total ascorbate pool when compared to the control grown on the auxin-free medium. Similar to auxin, adding DHA to the culture medium stimulated lateral root formation and inhibited primary root elongation. In contrast to DHA, ASC treatment affected significantly neither lateral root formation nor primary root growth and partly reversed the stimulatory effect of IAA on root formation and the inhibitory effect on root elongation. These results suggest that auxin induced changes in ascorbate metabolism may be involved in developmental reactions in tomato roots.

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Section: Discussioncontrasting

confidence: 45%

Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

2007

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“…In the apoplast of cultured rose cells, a portion of the DHA is oxidised to oxalate and l -threonate (and esters thereof), some of these reactions being proposed to generate H 2 O 2 , and a further portion of the DHA is hydrolysed to DKG [17], [18]. The balance between these two pathways (oxidation:hydrolysis ratio of DHA) is dictated by the severity of the ambient oxidising conditions [39], [38].…”

Section: Introductionmentioning

confidence: 99%

Metabolites of 2,3-diketogulonate delay peroxidase action and induce non-enzymic H 2 O 2 generation: Potential roles in the plant cell wall

Kärkönen

Dewhirst

Mackay

et al. 2017

Archives of Biochemistry and Biophysics

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A proportion of the plant's l-ascorbate (vitamin C) occurs in the apoplast, where it and its metabolites may act as pro-oxidants and anti-oxidants. One ascorbate metabolite is 2,3-diketogulonate (DKG), preparations of which can non-enzymically generate H2O2 and delay peroxidase action on aromatic substrates. As DKG itself generates several by-products, we characterised these and their ability to generate H2O2 and delay peroxidase action.DKG preparations rapidly produced a by-product, compound (1), with λmax 271 and 251 nm at neutral and acidic pH respectively. On HPLC, (1) co-eluted with the major H2O2-generating and peroxidase-delaying principle. Compound (1) was slowly destroyed by ascorbate oxidase, and was less stable at pH 6 than at pH 1. Electrophoresis of an HPLC-enriched preparation of (1) suggested a strongly acidic (pKa ≈ 2.3) compound. Mass spectrometry suggested that un-ionised (1) has the formula C6H6O5, i.e. it is a reduction product of DKG (C6H8O7).In conclusion, compound (1) is the major H2O2-generating, peroxidase-delaying principle formed non-enzymically from DKG in the pathway ascorbate → dehydroascorbic acid → DKG → (1). We hypothesise that (1) generates apoplastic H2O2 (and consequently hydroxyl radicals) and delays cell-wall crosslinking — both these effects favouring wall loosening, and possibly playing a role in pathogen defence.

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“…AsA has additionally been described to play an important role as an enzyme cofactor while participating in defense, cellular elongation, division and fruit ripening (Arrigoni and De Tullio, 2002; Pastori et al, 2003; Green and Fry, 2005). In humans, AsA has an integral role as cofactor of some dioxygenases enzymes which are involved in biosynthesis of carnitine and collagen (Padayatty et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

Pyrophosphate levels strongly influence ascorbate and starch content in tomato fruit

et al. 2013

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Ascorbate (vitamin C) deficiency leads to low immunity, scurvy, and other human diseases and is therefore a global health problem. Given that plants are major ascorbate sources for humans, biofortification of this vitamin in our foodstuffs is of considerable importance. Ascorbate is synthetized by a number of alternative pathways: (i) from the glycolytic intermediates D-glucose-6P (the key intermediates are GDP-D-mannose and L-galactose), (ii) from the breakdown of the cell wall polymer pectin which uses the methyl ester of D-galacturonic acid as precursor, and (iii) from myo-inositol as precursor via myo-inositol oxygenase. We report here the engineering of fruit-specific overexpression of a bacterial pyrophosphatase, which hydrolyzes the inorganic pyrophosphate (PPi) to orthophosphate (Pi). This strategy resulted in increased vitamin C levels up to 2.5-fold in ripe fruit as well as increasing in the major sugars, sucrose, and glucose, yet decreasing the level of starch. When considered together, these finding indicate an intimate linkage between ascorbate and sugar biosynthesis in plants. Moreover, the combined data reveal the importance of PPi metabolism in tomato fruit metabolism and development.

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Apoplastic degradation of ascorbate: Novel enzymes and metabolites permeating the plant cell wall

Cited by 32 publications

References 23 publications

Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

Exogenous auxin affects ascorbate metabolism in roots of tomato seedlings

Metabolites of 2,3-diketogulonate delay peroxidase action and induce non-enzymic H 2 O 2 generation: Potential roles in the plant cell wall

Pyrophosphate levels strongly influence ascorbate and starch content in tomato fruit

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