Involvement of Reactive Oxygen Species, Glutathione Metabolism, and Lipid Peroxidation in the Cf-Gene-Dependent Defense Response of Tomato Cotyledons Induced by Race-Specific Elicitors of Cladosporium fulvum

Abstract

The chronological order of responses to Cladosporium fulvum (Cooke) (Cf) race-specific elicitors was assessed in cotyledons of three near-isogenic tomato (Lycopersicon esculentum Mill.) lines carrying either Cf-9 or Cf-2 or no Cf gene. The responses observed were dependent on the presence of a Cf gene, Avr-gene product dose injected, and the relative humidity (RH) of the growth chamber. At ambient RH, superoxide formation and lipid peroxidation occurred after 2 h (Cf9) and 4 h (Cf2). At elevated RH (98%) and at lower avirulence elicitor dose, Cf-Avr-dependent lipid peroxidation was considerably attenuated. Significant electrolyte leakage occurred by 18 h but only at the lower RH. Total glutathione levels began to increase 2 to 4 h and 4 to 8 h after challenge of Cf9 and Cf2 cells, respectively, and by 48 h reached 665 and 570% of initial levels. A large proportion of this accumulation (87%) was as oxidized glutathione. When the RH was increased to 98%, increases in glutathione levels were strongly attenuated. lncreased lipoxygenase enzyme activity was detected 8 h postchallenge in either incompatible interaction. These results indicate that the activation of the Cf-Avr-mediated defense response results in severe oxidative stress.Early events during the interaction between a specialized pathogen and its host ultimately determine whether the attempted infection succeeds or fails. Plant-pathogen interactions often exhibit race-cultivar specificity. To explain this, the "gene-for-gene" hypothesis has been proposed (Flor, 1946), wherein incompatibility requires the presence of both a dominant plant resistance ( X ) gene and a complementary dominant pathogen avirulence (Aur) gene (Gabriel and Rolfe, 1990;Keen, 1990).The interaction between the fungal pathogen Cladosporium fuluum (syn. Fulua fulua [Cooke] Cif.) and tomato (Lycopersicon esculentum Mill.) provides an excellent experThis work was supported by a Glasstone research fellowship to M.J.M. and the Gatsby Charitable Foundation to K

The hypersensitive response and the induction of cell death in plants

“…For example, certain puri®ed elicitors can induce many of the physiological changes occurring during disease resistance (Nu È rnberger et al, 1994) and lesions resembling the HR (He et al, 1993;May et al, 1996). Therefore the destructive potential of an active pathogen is not necessary.…”

“…A membrane NADPH oxidase analogous to that found in mammalian neutrophils may be involved in this process (Groom et al, 1996). ROIs could also act as a signal via the production of lipid peroxides (May et al, 1996;Mehdy, 1994). The XR is characterized by an uptake of Ca 2+ (Levine et al, 1996) and export of Cl 7 and K + driven by H + -ATPases, resulting in alkalinization of the cytoplasm (Atkinson and Baker, 1989).…”

“…The earliest changes observed following pathogen recognition are an oxidative burst, resulting in production of Reactive Oxygen Intermediates (ROIs) (Baker and Orlandi, 1995;Levine et al, 1994;May et al, 1996) and rapid ion fluxes across the plasma membrane, termed the XR (Atkinson and Baker, 1989). There is some debate concerning the nature of the ROIs involved.…”

Induction of defense responses in tobacco by the protein Nep1 from Fusarium oxysporum

“…The delay could be explained by inherent antioxidant mechanisms within the plant cells that were able to counter any initial H 2 O 2 burst induced by the low concentration of Nep1. May et al [53] measured induced responses in near-isogenic lines of tomato by race-specific A6r-gene products from C. ful6um. The elicitors induced the production of reactive oxygen species, including H 2 O 2 , and caused increases in glutathione levels and lipoxygenase enzyme activity.…”

Post-Transcriptional Suppression of Cytosolic Ascorbate Peroxidase Expression during Pathogen-Induced Programmed Cell Death in Tobacco

“…In plants, this response is termed the hypersensitive response (HR) and results in the formation of a zone of dead cells around the infection site, the synthesis of salicylic acid (SA), and the accumulation of antimicrobial agents, such as pathogenesis-related (PR) proteins and phytoalexins (Goodman and Novacky, 1994;Dangl et al, 1996; HammondKosack and Jones, 1996). The layers of dead cells that surround the site of pathogen entry are thought to function as a physical barrier that inhibits further proliferation and spread of the pathogen (Goodman and Novacky, 1994).PCD that occurs during the HR is accompanied by an increase in the production of reactive oxygen species (ROS) and lipid peroxidation (Doke and Ohashi, 1988;Mehdy, 1994;Hammond-Kosack and Jones, 1996;May et al, 1996; Yang et al, 1997). Recent studies have indicated that reactive oxygen intermediates in the form of H 2 O 2 and are key mediators of PCD during the HR (Levine et al, 1994, O 2 • Ϫ 1996; Jabs et al, 1996;Draper, 1997;Shirasu et al, 1997) and may function as part of a signal transduction pathway leading to the induction of PR proteins and systemic resistance in infected and noninfected parts of the plant (Chen et al, 1993;Green and Fluhr, 1995).…”