Centaurea maculosa

Asteraceae, Milliaceae and Apiaceae, are among some plant families that are known to have insecticidal constituents. Vulgar-one B (isolated from Artemisia douglasiana Asteraceae), apiol (isolated from Ligusticum hultenii Apiaceae), and cnicin (isolated from Centaurea maculosa Asteraceae) cause significant mortality to Formosan subterranean... 

Flavonoids are important secondary metabolites involved in pigmentation of flowers, disease resistance, and so on. Among the flavonoids, kaempferol (67), quercetin (68), and naringenin (69) are most often cited as allelochemicals. (zh)-Catechin was identified in the root exudates from spotted knapweed Centaurea maculosa) as the compound responsible for its invasive behavior.45 The plant uses (-)-catechin (70) as an allelochemical facilitating its invasion and (+)-catechin (71) as a defense compound against pathogens. 

At the outset of this study we chose to examine Centaurea maculosa L. (spotted knapweed), a species of Immense economic importance in the northwestern United States. This plant threatens forage production of millions of acres of rangeland in this region... 

Bais, H.P., Walker, T.S., Kennan, A.J., Stennitz, RR. Vivanco, J.M. (2003). Structure-dependent phytotoxicity of catechins and other flavonoids flavonoid conversions by ceU-lree protein extracts of Centaurea maculosa (spotted knapweed) roots. Journal of Agricultural and Food... 

Allelopathic processes via (-)-catechia (2S,3R-enantiomer) (Fig. 1) have been invoked to partially explain the snccess of Centaurea maculosa (spotted knapweed) in North America [46-48], Throngh bioassays, root exnded (-)-catechin was identified as the pntative allelochemical of spotted knapweed, and mnltiple stndies have examined varions facets of the role of this compound as an allelochemical [46-51 ]. The 2R,3S-(+)-catechin enantiomer is also produced by the plant, but was reported essentially to be nonphytotoxic. This work supported the novel weapons hypothesis, which states that the success of some exotic invasive plant species may be due to the production of allelochemicals that native species have never encountered and, thus, to which they have not evolved defenses [52]. 

Weir, T.L. et al. (2006) Oxalate contributes to the resistance of Gaillardia grandiflora and Lupinus sericeus to a phytotoxin produced by Centaurea maculosa. Planta 223, 785-795... 

Diffuse (Centaurea diffusa) and spotted knapweed (C. maculosa) are two introduced weeds that have expanded to occupy large areas of rangeland in the dry Interior of the Pacific Northwest. The apparent ability of knapweed to invade established, productive rangeland has been attributed to the action of allelochemicals produced by knapweed (i., ). The potential allelopathic effect of plants such as knapweed is an area of considerable Interest, with researchers looking to exploit this phenomenon in agricultural situations, or simply to explain patterns of plant distribution ( ). 

In one of the original papers of the Vivanco laboratory [46], the mechanism of action of (-)-catechin was linked to induction of ROS. This is debatable since catechins are well known antioxidants (e.g. [62]). In fact, more than 1500 papers mention catechin as an antioxidant (SciFinder search, as of February 2008). Finally, Qin et al. [63] found no evidence of root exudate-mediated allelopathy with Centaurea solstitialis, but the authors apparently did not determine if this species produces ( )-catechin. If it were to produce similar amounts of ( )-catechin as C. maculosa, it would be strong evidence of the lack of allelo-pathic influence of these compounds. 

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