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Abstract
In the plant apoplast, ascorbate is oxidised, via dehydroascorbic acid, to O-oxalyl esters [oxalyl-L-threonate (OxT) and cyclic oxalyl-L-threonate (cOxT)]. We tested whether OxT and cOxT can donate the oxalyl group in transacylation reactions to form oxalyl-polysaccharides, potentially modifying the cell wall. [oxalyl-14C]OxT was incubated with living spinach (Spinacia oleracea) and Arabidopsis cell-suspension cultures in the presence and absence of proposed acceptor substrates (carbohydrates). In addition, [14C]OxT and [14C]cOxT were incubated in vitro with cell-wall enzyme preparations plus proposed acceptor substrates. Radioactive products were monitored electrophoretically. Oxalyltransferase activity was detected. Living cells incorporated oxalate groups from OxT into cell-wall polymers via ester bonds. When sugars were added, [14C]oxalyl-sugars were formed, in competition with OxT hydrolysis. Preferred acceptor substrates were carbohydrates possessing primary alcohols e.g. glucose. A model transacylation product, [14C]oxalyl-glucose, was relatively stable in vivo (half-life >24 h), whereas [14C]OxT underwent rapid turnover (half-life ~6 h). Ionically wall-bound enzymes catalysed similar transacylation reactions in vitro with OxT or cOxT as oxalyl donor substrates and any of a range of sugars or hemicelluloses as acceptor substrates. Glucosamine was O-oxalylated, not N-oxalylated. Plants possess apoplastic acyltransferase (oxalyltransferase) activity that transfers oxalyl groups from ascorbate catabolites to carbohydrates, forming relatively long-lived O-oxalyl-carbohydrates. The findings increase the range of known metabolites whose accumulation in vivo indicates vitamin C catabolism. Possible signalling roles of the resulting oxalyl-sugars can now be investigated, as can the potential ability of polysaccharide oxalylation to modify the wall's physical properties.
Original language | English |
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Pages (from-to) | 743–757 |
Number of pages | 15 |
Journal | The Plant Journal |
Volume | 95 |
Early online date | 8 Jun 2018 |
DOIs | |
Publication status | Published - 2 Aug 2018 |
Keywords
- Arabidopsis
- apoplast
- cell-suspension culture
- cell-wall modification
- oxalic acid
- oxalyl-sugars
- oxalyl-threonate
- spinach
- vitamin C
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- 1 Finished
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Tracing the turnover of vitamin C in harvested salad tissues
UK industry, commerce and public corporations
1/10/11 → 30/09/15
Project: Research