title: Temporal regulation of cell-wall pectin methylesterase and peroxidase isoforms in cadmium-treated flax hypocotyl.
abstract: OBJECTIVE
  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(NO(3))(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.
  
  
  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.
authors.affiliation: Laboratory Glyco-Mev, SCUEOR, IFRMP 23, University of Rouen, 76821 Mont Saint Aignan Cedex, France. florence.paynel@univ-rouen.fr
authors.forename: Florence
authors.initials: F
authors.lastname: Paynel
authors.forename: Annick
authors.initials: A
authors.lastname: Schaumann
authors.forename: Mustapha
authors.initials: M
authors.lastname: Arkoun
authors.forename: Olfa
authors.initials: O
authors.lastname: Douchiche
authors.forename: Claudine
authors.initials: C
authors.lastname: Morvan
mesh_terms: D002104:Cadmium; D002265:Carboxylic Ester Hydrolases / Q000235:genetics / Q000378:metabolism*; D002473:Cell Wall / Q000201:enzymology*; D019597:Flax / Q000201:enzymology* / Q000235:genetics; D015870:Gene Expression; D018546:Hypocotyl / Q000502:physiology; D007527:Isoenzymes / Q000378:metabolism; D010368:Pectins / Q000378:metabolism*; D009195:Peroxidase / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D002104:Cadmium; D010368:Pectins; D009195:Peroxidase; D002265:Carboxylic Ester Hydrolases; C022323:pectinesterase; C003181:polygalacturonic acid