Finally, proof of weapons of mass destruction.

Allelopathy (one species' use of chemicals to harm other species) may be a key ingredient in successful invasions of alien plants into established communities. Bais et al. show that in response to elicitation by common soil fungi, spotted knapweed (Centaurea maculosa) launches an ineffective defense against the fungi that results in extensive collateral damage to neighboring plants. Specifically, the flavonoid (-)-catechin, released from the roots of knapweed, produces a massive reactive oxygen species (ROS)-mediated oxidative burst, Ca2+ signaling, and rapid cell death in those unadapted native species whose habitats the plant regularly invades. The roots release both (+) and (-) enantiomers, but only the (-) enantiomer functions as a weapon of mass destruction; the (+) enantiomer inhibits the growth of numerous common soil-borne bacterial pathogens. Eliciting apoptotic response for a competitive advantage is an example of signal cross-talk between the genomes of interacting organisms and highlights how the internal signaling of one organism can be used by others to adjust their phenotypes in an adaptive manner. The study provides strong circumstantial evidence for an allelopathic interaction, but the genetic manipulation of (-)-catechin release would allow researchers to determine if these responses occur in nature. Precise genetic control over the release of secondary metabolites from plants would benefit ecological research.