Fatty Acid Hydroperoxides and H2O2 in the Execution of Hypersensitive Cell Death in Tobacco Leaves  

Abstract

We initially compared lipid peroxidation profiles in tobacco (Nicotiana tabacum) leaves during different cell death events. An upstream oxylipin assay was used to discriminate reactive oxygen species (ROS)-mediated lipid peroxidation from 9-and 13-lipoxygenase (LOX)-dependent lipid peroxidation. Free radical-mediated membrane peroxidation was measured during H 2 O 2 -dependent cell death in leaves of catalase-deficient plants. Taking advantage of these transgenic plants, we demonstrate that, under light conditions, H 2 O 2 plays an essential role in the execution of cell death triggered by an elicitor, cryptogein, which provokes a similar ROS-mediated lipid peroxidation. Under dark conditions, however, cell death induction by cryptogein was independent of H 2 O 2 and accompanied by products of the 9-LOX pathway. In the hypersensitive response induced by the avirulent pathogen Pseudomonas syringae pv syringae, both 9-LOX and oxidative processes operated concurrently, with ROS-mediated lipid peroxidation prevailing in the light. Our results demonstrate, therefore, the tight interplay between H 2 O 2 and lipid hydroperoxides and underscore the importance of light during the hypersensitive response.Different defense mechanisms are used by plants to cope with pathogen assaults. A major source of resistance is conditioned by the interaction between plant resistance and pathogen avirulence gene products (Martin et al., 2003;Rathjen and Moffett, 2003). This defense strategy is characterized by (1) the activation of the hypersensitive response (HR), typified by a localized programmed cell death activation; (2) the initiation of defense responses, including cell wall reinforcement, accumulation of phytoalexins, and expression of antimicrobial proteins; and (3) the onset of a local and systemic acquired resistance (Lamb and Dixon, 1997;Beers and McDowell, 2001;Greenberg and Yao, 2004).The signaling cascades leading to the HR are starting to be elucidated. Several resistance genes have been cloned, and protein kinases, phosphatases, and GTP-binding proteins have all been implicated downstream of these recognition proteins (Martin et al., 2003;Rathjen and Moffett, 2003). Changes in ion fluxes across the plasma membrane and the production of reactive oxygen species (ROS) and nitric oxide (NO) are among the earliest events following pathogen infection or elicitor treatment in cultured plant cells (Doke, 1997;Grant and Loake, 2000;Wendehenne et al., 2004). The production of ROS is biphasic, with a sustained second oxidative burst in response to an avirulent pathogen, and monophasic and transient with a virulent pathogen. This suggests that ROS production may be responsible for some of the defense-associated processes (Lamb and Dixon, 1997). Furthermore, ROS, and specifically H 2 O 2 , are key modulators of NO in triggering plant cell death (Delledonne et al., 2001;Neill et al., 2002;Wendehenne et al., 2004).In order to obtain further insight into the role of H 2 O 2 in plant signaling and cell death, we used transgenic tobacco ...

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Maize death acids, 9-lipoxygenase–derived cyclopente(a)nones, display activity as cytotoxic phytoalexins and transcriptional mediators

“…As mediators, metabolites derived from the 9-LOX pathway in pepper (Capsicum annuum) and Arabidopsis positively regulate defense and cell death responses to diverse pathogens (21). Despite numerous studies linking the 9-LOX pathway to cell death processes (24)(25)(26), many oxylipin identities, activities, and links to enzyme activation remain unknown (27,28). As a positional isomer of 12-OPDA, the 9-LOX oxylipin 10-oxo-11,15-phytodienoic acid (10-OPDA) and the 18:2-derived 10-oxo-11-phytoenoic acid (10-OPEA) are structurally similar to jasmonates (29).…”

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“…1A). Such oxylipins accumulate upon pathogen attack (Rustérucci et al, 1999;Göbel et al, 2002;Montillet et al, 2005), and they may play significant roles in plant-pathogen interactions. They could act directly through their antimicrobial properties (Prost et al, 2005) and/or they could be components of signaling pathways leading to defense responses.…”