Soluble and Cell Wall Peroxidases in Reed Canarygrass in Relation to Disease Resistance and Localized Lignin Formation

Abstract

The relationship of peroxidases to an indudble disease-resistance mechanism involving lignification of leaf epidermal cell walls was studied. Reed canargrass (Phalaris arundinacea L.) leaf discs were inoculated with Helminthosporium avenae Eidam and floated on water. In inoculated discs, the activity of soluble, ionic wall-bound and covalent wal-bound peroxidases was about twice the level of activity in noninoculated discs. The increase was attributable to increases in activity of three cathodic isoperoxidases and to the appearance of a new cathodic isoperoxidase. Peroxidase activity in cryostat microtome sections of inoculated discs was histochemically localized in the wail near the site of attempted penetration. When inoculated discs were floated on solutions of cydoheximide (25 ,lg/ml), increases in peroxidase activity were inhibited, and the fungus penetrated the tissue. The inhibition of peroxidase activity was related to inhibition of cathodic isoperoxidase activity. Anodic isoperoxidase activity did not show changes in response to inoculation or cydoheximide treatment.It was suggested that the resistance mechanism in P. arundinacea involves an induction of cathodic isoperoxidases in challenged tissue. These peroxidshes may function in the biosynthesis of lignin at the site of attempted penetration.Plant peroxidases have been extensively investigated with regard to their role in resistance to fungal, viral, and bacterial diseases (14, 15). Peroxidases have also been strongly implicated in lignin biosynthesis (5, 13). Recent studies have implicated lignin formation in the cell walls of reed canarygrass and wheat as a resistance response (11,12,16,17). Vance and Sherwood (17) showed that when the resistance response in reed canarygrass was inhibited by cycloheximide, lignin biosynthesis and activity of soluble enzymes (including peroxidase) involved in lignin biosynthesis were also inhibited. Since the cell wall provides the initial interface between the pathogen and the host, cell wall components such as lignins and peroxidases may be closely involved in the plant's response to a pathogen.In this study, we have investigated soluble and cell wall peroxidases of reed canarygrass. We have also investigated the localization of peroxidases around the attempted penetration site. The results are discussed in relation to lignin formation and disease resistance in reed canarygrass. (9) was grown in a glasshouse bed of peatmoss-vermiculite. Leaf discs (8-mm diameter) were cut with a corkborer from unblemished, expanded leaves. The discs were floated on distilled H20 or aqueous solutions of cycloheximide (25 ,ug/ml) in Petri dishes. The upper surface of the disc was thoroughly sprayed with a suspension of Helminthosporium avenae Eidam spores or a 0.05-ml drop of spore suspension was pipetted directly onto the disc. The preparation of inoculum was described previously (16).Cell-free extracts were obtained from samples collected 18 hr after inoculation. The samples were freeze dried. Cell wall and protoplas...

Elicitation of Lignin Biosynthesis and Isoperoxidase Activity by Pectic Fragments in Suspension Cultures of Castor Bean

“…The search for such a correlation is complicated by the fact that the rate and extent of spread of an invading fungus are usually much greater in compatible interactions. The appearance of new isoenzymes ofperoxidase in infected tissue has also been previously reported (15,31,33,37 (32). Calcium ions displace the bound enzymes from their interaction with pectic cell wall components and also eliminate their interaction with pectic elicitor, thus allowing their free migration into gels.…”

“…Measurable peroxidase activity can frequently increase severalfold above control levels in infected plants, and in some cases these increases are attributable to increases in the activities of specific isoenzymes. In a fewer number ofinstances, disease-specific isoperoxidases have been seen to appear in infected tissues (15,31,33,37 (23). To stop hydrolysis, solutions were brought to pH 6.4 with concentrated NaOH and then autoclaved.…”

Plant gene expression in response to pathogens

“…The measurable activities of several enzymes associated with lignification increased in leaf discs of the grass Phalaris arundinacea following challenge with the non-host pathogenic fungus Helminthosporium avenae [192]. In this interaction low pI (cathodic) but not high pI (anodic) peroxidase isozymes were induced [190]. Similarly, increases in peroxidase and polyphenol oxidase activities were associated with resistance in mung bean (Vigna radiata) induced by Rhizoctonia solani and ethephon (which releases ethylene) [6].…”

High Resolution of Peroxidase-Indoleacetic Acid Oxidase Isoenzymes from Horseradish by Isoelectric Focusing

“…What is the significance of some peroxidase isoenzymes being located in all parts of a cell while other peroxidase isoenzymes are located only in particular organelles, membranes, or walls? Peroxidase is thought to be involved in lignin formation (12). Are all peroxidase isoenzymes associated with this activity, or are just certain isoenzymes involved?…”