Race-Specific Elicitors of Cladosporium fulvum Induce Changes in Cell Morphology and the Synthesis of Ethylene and Salicylic Acid in Tomato Plants Carrying the Corresponding Cf Disease Resistance Gene

Abstract

New Brunswick, New Jersey 08903-0231 (P.S., I.R.)Defense responses mediated by the genetically unlinked Cf-9 and Cf-2 genes were compared with those involving no Cf gene (CfO). Compatible tomato (Lycopersicon esculentum)-Cladosporiom fulvum intercellular washing fluids were injected into tomato cotyledons, and the kinetics of responses was monitored under conditions of 70 and 98% relative humidity. l h e latter conditions suppressed the normal macroscopic responses. For the Cf-9-Avr9 interaction, stomatal opening was induced within 3 to 4 h and after 9 h mesophyll cell death commenced. A burst of ethylene production occurred between 9 and 12.5 h and remained elevated. Free salicylic acid levels increased after 12 h, peaked at 24 h, and thereafter declined. For the Cf-2-Avr2 interaction, stomata became plugged after 8 h, and salicylic acid and ethylene levels increased by 12 and 1 8 h, respectively, and thereafter declined. Host cell death commenced around vascular tissue by 24 h. Cell death in both incompatible interactions was frequently preceded by cell enlargement. For CfO-injected plants, no significant responses were detected. High humidity delayed and reduced the Cf-Avr-gene-dependent cell death and ethylene synthesis, whereas induced salicylic acid levels were unaffected for Cf-2-Avr2 and reduced in magnitude only for Cf-9-A vr9.An array of highly localized plant defenses are induced rapidly and coordinately at the site of genetically incompatible plant-pathogen interactions. Subsequently, the growth of the invading virus, bacteria, fungus, or nematode is retarded, and eventually the microbe either dies or remains quiescent. Activation of localized plant defenses is dependent on mutual recognition between plant and microbe. This recognition is hypothesized to result from the interaction of the product of a dominant or semidominant

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

“…However, in the case of Cf9 treatments at 48 h, the extractable LOX activity was highly variable. These data are thought to reflect the fact that cotyledons at this stage were almost uniformly necrotic and inviable (Hammond-Kosack et al, 1996). In the absence of Cf genes, there was a slight increase in LOX activity by 24 h a.i.…”

“…Both C/-2-and C/-9-dependent accumulation of TEARS was almost completely abolished. Under these environmental conditions the macroscopic response to IF injection is abolished (Hammond-Kosack et al, 1996).…”

“…The concerted deployment of genetic, biochemical, and molecular techniques will be necessary to reveal how Cf-gene products activate effective defense upon Avr-gene product recognition. This point is further elaborated by Hammond-Kosack et al (1996).…”

“…For the challenged Cf9 plants, the effect of higher humidity can probably best be explained by the elimination of the desiccation process associated with the induced supraoptimal opening of stomata, reporteci by Hammond-Kosack et al (1996). However, for Cf2 plants alternative explanations are required because of the lack of elicitor-induced stomatal opening.…”

“…Both lines of evidence support the hypothesis that Cfprotein activation has a profound impact on the loss of cellular homeostasis of Avr-elicitor-treated tissues containing the necessary Cf gene. These changes in turn preceded changes in cell viability (Hammond-Kosack et al, 1996) and are likely to play an important role in cell death. The whole-plant system used in this study allows correlations to be made between the effect of early responses to Cf-gene action (superoxide generation) on the physiology of the host.…”