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Temporal regulation of cell-wall pectin methylesterase and peroxidase isoforms in cadmium-treated flax hypocotyl

Paynel, Florence, Schaumann, Annick, Arkoun, Mustapha, Douchiche, Olfa, Morvan, Claudine
Annals of botany 2009 v.104 no.7 pp. 1363-1372
Linum usitatissimum, cadmium, cohesion, crosslinking, enzyme activity, flax, genes, hypocotyls, isoelectric focusing, pectinesterase, peroxidase, proteins, seedlings
BACKGROUND AND AIMS: In hypocotyls of flax (Linum usitatissimum) cadmium-induced reorientation of growth (i.e. an increase in expansion and a decrease in elongation) coincides with marked changes in the methylesterification and cross-linking of homogalacturonans within various cell-wall (CW) domains. The aim of the present study was to examine the involvement of pectin methylesterase (PME) and peroxidase (PER) in this cadmium-induced CW remodelling. METHODS: CW proteins were extracted from hypocotyls of 10- and 18-d-old flax that had been treated or not treated with 0·5 mM Cd(NO₃)₂. PME and PER expression within these extracts was detected by LC/MS, by isoelectric focusing and enzyme activity assays. Transcript expression by RT-PCR of known flax PME and PER genes was also measured in corresponding samples. KEY RESULTS: In cadmium-treated seedlings, PME activity increased as compared with controls, particularly at day 10. The increased activity of PME was accompanied by increased abundance of both a basic protein isoform (B2) and a particular transcript (Lupme5). In contrast, induction of PER activity by cadmium was highest at day 18. Among the four reported PER genes, Flxper1 and 3 increased in abundance in the presence of cadmium at day 18. CONCLUSIONS: The temporal regulation of Lupme and Flxper genes and of their respective enzyme activities fits the previously reported cadmium-induced structural changes of homogalacturonans within the CWs. After PME-catalysed de-esterification of homogalacturonans, their cross-linking would depend on the activity of PERs interacting with calcium-dimerized blocks and reinforce the cell cohesion during the cadmium-induced swelling.