title: Purification and Partial Characterization of Tomato Extensin Peroxidase.
abstract: Early plant defense response is characterized by elevation of activity of peroxidases and enhanced insolubilization of hydroxyproline-rich glycoproteins, such as extensin, in the cell wall. The insolubilization process (cross-linking between soluble extensin precursor molecules) is catalyzed by extensin peroxidases. We have ionically eluted extensin peroxidases from intact water-washed suspension-cultured tomato (hybrid of Lycopersicon esculentum Mill. and Lycopersicon peruvianum L. [Mill.]) cells and purified them to homogeneity by molecular sieve and cation-exchange chromatography. Four ionic forms of peroxidase (PI,PII,EPIII, and EPIV) were resolved; only the latter two cross-linked tomato soluble extensin. The molecular weight (34,000-37,000), amino acid composition, and isoelectric point (9.0) of the extensin peroxidases were determined. Substrate specificities of the enzymes were investigated: soluble extensin and potato lectin (a hydroxyproline-rich glycoprotein with a domain that strongly resembles extensin) were cross-linked by only two forms of the enzyme, whereas bovine serum albumin, aldolase, insulin, a number of other marker proteins, and proteins eluted from tomato cells (except extensin) could not be cross-linked. We have also isolated a yeast elicitor that enhances total peroxidase activity and extensin insolubilization within 1 h of challenge in cultured cells of tomato. A highly sensitive enzyme-linked immunosorbent assay technique using polyclonal antiserum raised against soluble tomato extensin was used to demonstrate extensin insolubilization in vivo. A tomato cell-wall peroxidase that cross-links extensin has been purified and may have a role in plant defense.
authors.affiliation: School of Applied Science, South Bank University, 103 Borough Road, London, United Kingdom SE1 0AA (M.D.B., N.A., M.T., M.F.C.).
authors.forename: M. D.
authors.initials: MD
authors.lastname: Brownleader
authors.forename: N.
authors.initials: N
authors.lastname: Ahmed
authors.forename: M.
authors.initials: M
authors.lastname: Trevan
authors.forename: M. F.
authors.initials: MF
authors.lastname: Chaplin
authors.forename: P. M.
authors.initials: PM
authors.lastname: Dey