Biochemistry of Invasion

Centaurea maculosa (spotted knapweed) is one of the worst exotic invaders plaguing the western United States. In 2003, my lab isolated catechin, an allelopathic chemical exuded by C. maculosa roots, and demonstrated that this chemical persists in the soil surrounding spotted knapweed roots and is capable of inhibiting the germination of seeds of other species (Bais et al. 2003). Interestingly, plants native to North America are far more susceptible to catechin than plants from its native habitat in Eurasia; furthermore, the concentration of catechin in soils under spotted knapweed is twice as high in North America as it is in Europe. The differential susceptibility of North American and European plant species to the root-secreted phytotoxin of alien invasive knapweed species has been hailed as evidence that allelopathy can facilitate biological invasions (Baldwin 2003; Fitter 2003). Hierro and Callaway (2003) point out that allelopathy may be more important in invaded plant communities because competing plants are more likely to be naïve to the chemicals possessed by newly arrived species. This idea has been called the “novel weapons” hypothesis. Additionally, our work indicates that different levels of resistance and susceptibility to catechin exist in plant populations (Weir et al. 2003), suggesting that the capability of C. maculosa to invade an area through allelochemistry may be affected by the age, species composition, and prior exposure to spotted knapweed of plants in that particular area. We are currently conducting research using this system to dissect the combined ecological, molecular, and biochemical cascades involved in catechin’s rhizotoxicity. The use of the model plant species Arabidopsis has allowed us to unravel previously unknown cell death cascades initiated by catechin.

Works Cited:

Bais, H.P., Vepachedu, R., Gilroy, S., Callaway, R.M., and Vivanco, J.M. (2003) Allelopathy and exotic plant invasion: from molecules and genes to species interactions. Science 301:1377-1380

Baldwin, IT (2003) At last, evidence of weapons of mass destruction. Science STKE, pe42 (online)

Fitter, A (2003) Making allelopathy respectable. Science 301: 1337-1338

Hierro, JL and Callaway, RM (2003) Allelopathy and exotic plant invasion. Plant Soil 256: 25-39

Weir TL, Bais HP, Vivanco JM (2003) Intraspecific and interspecific interactions mediated by a phytotoxin, (-) catechin, secreted by the roots of Centaurea maculosa (spotted knapweed). J. Chem. Ecol. 29: 2397-2412