Plant Disease Resistance

Edited by Thomas W. Durso A. Levine, R. Tenhaken, R. Dixon, C. Lamb, "H2O2 from the oxidative burst orchestrates the plant hypersensitive disease resistance response," Cell, 79:583-93, 1994. (Cited in more than 80 publications through August 1996) Comments by Chris Lamb, Salk Institute for Biological Studies, La Jolla, Calif. 'A VERY ACTIVE AREA': Chris Lamb notes that a burst of hydrogen peroxide causes invaded cells to die and helps protect surrounding cells. Plants under attack from invading pathogens respond with a variety of defense mechanisms, including the production of oxidants such as hydrogen peroxide (H2O2). In addition, this so-called hypersensitive response often results in the death of the cell being invaded. In this paper, researchers were able to show a causal relationship, rather than a mere correlation, between the oxidative burst and the hypersensitive cell death, according to Chris Lamb, a professor of plant biology at the Salk Institute for Biological Studies in La Jolla, Calif. "We showed that the hydrogen peroxide generated was a signaling agent, inducing key aspects in the hypersensitive response including death of the challenged cell and activation of cellular protectant genes in surrounding cells," Lamb reports. "This work shows that key components of the hypersensitive response were driven by the oxidative burst." The research was part of a joint project between the Salk Institute and the Noble Foundation of Ardmore, Okla., on the mechanism of plant disease resistance. It grew out of a study in which the oxidative burst was found to mediate cross-linking of proteins in plants' cell walls (D.J. Bradley et al., Cell, 20:21-30, 1992). Lamb explains that much of today's work in disease resistance involves attempts to clone resistance genes and understand how their products-enzymes involved in cellular protection-act. "Our work flags the oxidative burst as a central player in the downstream responses and therefore provides a focus for mechanistic studies both of the signal pathway between the receptor and oxidant-generating systems, and how oxidants trigger programmed cell death. "In practical terms, as we understand the mechanisms of natural disease resistance in plants, we may be able to devise new ways of manipulating enhanced, durable, broad-spectrum protection," he adds. Lamb credits the paper's high citation rate to its applicability to the expanding field of disease-resistance research, and its overlap with oxidant-mediated signaling in animals. "Because the oxidative burst is a good correlative expression of disease resistance,understanding that it's a key player focuses attention on the signal transduction pathway between pathogen reception, putatively by the resistance gene product, and activation of the oxidative burst," he states. "That's a very active area right now." Since the publication of this paper, Lamb's team has discovered that "hydrogen peroxide triggers a massive calcium influx that activates a cell-death mechanism" similar to apoptosis in animals (A. Levine et al., Current Biology, 6:427-37, 1996). Subsequent research by Lamb and others showed that the oxidative cross-linking of proteins in the cell wall strengthens it and helps protect the plant from disease (L.F. Brisson et al., Plant Cell, 6:1703-12, 1994).Finally, Lamb says, there are indications that his team's research is turning heads beyond the plant world. "There's also a lot of interest in oxidants in the mammalian field, in neurodegenerative disease and the immune system, for example," he declares. "Some biomedical scientists decided this [paper] was relevant."

Plant Disease Resistance

The Scientist Staff

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