title: Role of extensin peroxidase in tomato (Lycopersicon esculentum Mill.) seedling growth.
abstract: It is proposed that inhibition of extensin peroxidase activity leads to a less rigid cell wall and thus promotes cell expansion and plant growth. A low-molecular-weight inhibitor derived from the cell walls of suspension-cultured tomato cells was found to completely inhibit extensin peroxidase-mediated extensin cross-linking in vitro at a concentration of 260 microg/ml. The inhibitor had no effect upon guaiacol oxidation catalyzed by extensin peroxidase or horseradish peroxidase. We have demonstrated that the light-irradiated inhibition of plant growth may be partially offset by inhibition of endogenous extensin peroxidase activity. Overall plant growth was enhanced by up to 15% in the presence of inhibitor relative to control plants. Inhibitor-treated and illuminated tomato hypocotyls grew up to 15% taller than untreated controls. The inhibitor had no effect upon etiolated plants over a 15-d period, suggesting that only low levels of peroxidase-mediated cross-linking can be found in the cell walls of etiolated plants. SDS-PAGE/Western blots of ionically bound protein from both etiolated and illuminated hypocotyls identified a doublet at 57/58.5 kDa which is immunoreactive with antibodies raised to tomato extensin peroxidase. Levels of the 58.5-kDa protein, determined by SDS-PAGE, were at least threefold higher in illuminated tomato hypocotyls than in etiolated hypocotyls. Three fold higher levels of extensin peroxidase, elevated in-vitro extensin cross-linking activity and 15% higher levels of cross-linked, non-extractable extensin were observed in illuminated tomato hypocotyls compared with etiolated tomato hypocotyls. This suggests that white-light inhibition of tomato hypocotyl growth appears to be mediated, at least partially, by deposition of cell wall extensin, a process regulated by Mr-58,500 extensin peroxidase. Our results indicate that the contribution of peroxidase-mediated extensin deposition to plant cell wall architecture may have an important role in plant growth.
authors.affiliation: School of Biosciences, University of Westminster, London, UK. brownlm@westminster.ac.uk
authors.forename: M D
authors.initials: MD
authors.lastname: Brownleader
authors.forename: J
authors.initials: J
authors.lastname: Hopkins
authors.forename: A
authors.initials: A
authors.lastname: Mobasheri
authors.forename: P M
authors.initials: PM
authors.lastname: Dey
authors.forename: P
authors.initials: P
authors.lastname: Jackson
authors.forename: M
authors.initials: M
authors.lastname: Trevan
mesh_terms: D002473:Cell Wall / Q000378:metabolism; D002478:Cells, Cultured; D006023:Glycoproteins / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D010544:Peroxidases / Q000378:metabolism*; D010940:Plant Proteins / Q000378:metabolism
chemical_list: D006023:Glycoproteins; D010940:Plant Proteins; C005488:extensin protein, plant; D010544:Peroxidases