Spotted knapweed

Cyclo(Pro-Tyr), also known as maculosin, is a phytotoxin produced by the fungus Altemaria alternata, and has been found to cause black necrotic lesions on the leaves of spotted knapweed. The mechanism underlying the phytotoxic action of cyclo(Pro-Tyr) may lie in its ability to inhibit ribulose-l,5-diphosphate carboxylase. ... 

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 ( ). 

Bais, H.P., Walker, T.S., Stermitz, F.R., Hufbauer, R.A., Vivanco, J.M. 2002. Enantiomeric-dependentphytotoxic and antimicrobial activity of ( )-catechin. A rhizosecreted racemic mixture from spotted knapweed. Plant Physiol 2003 128 1173-1179. 

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. 

A Host-Specific Phytotoziii from AtUrnana altemata on Spotted Knapweed... 

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... 

Only compounds 1 and 2 were phytotoxic to spotted knapweed 1 was at least an order of magnitude more toxic than 2. The molecular formula of 1 was determined to be by high... 

A phytotoxin may require binding sites within a plant in order to affect it adversely (1, 14). In the case of maculosin, a host specific toxin, a very specific receptor site may exist in spotted knapweed. Such a site may be a protein that has a normal role in the maintenance of cellular function, but coincidentally serves as a phytotoxin receptor (li, 15). Binding of the toxin by the receptor may result in a disruption in the functional role of the protein or result in a cascade effect involving other proteins. Either effect could result in cellular death (1, 111. 

In preliminary studies, the binding of C-maculosin was noted in the cytosolic (soluble) fraction of a spotted knapweed leaf extract, and little if any in the insoluble fraction. Binding activity was reduced or destroyed by treatment of the soluble fraction with heat or proteases, suggesting that the toxin receptor is a protein. Purification of the receptor has been pursued successfully using size exclusion column chromatography combined with affinity chromatography. The affinity support consists of epoxy activated Sepharose 6B to which synthetic maculosin has been attached. Further work should reveal the role of the receptor in the process of toxin-induced symptom production. 

Three to five days after treating spotted knapweed leaves with t-maculosin, and after necrotic symptoms appear, virtually all of the x-maculosin is converted to at least 3 other compounds. These compounds are insoluble in ethylacetate and soluble in methanol. 

Besides diketopiperazines, there are two other classes of phytotoxins produced by A. a1ternata on spotted knapweed tetramic acids and perylenequinones (1 ). Both groups of compounds are nonhost specific and require relatively large concentrations for biological activity to be expressed, eg. (IS). These... 

Both catechin enantiomers are secreted as a racemic mixture through the roots of spotted knapweed (Figure 22.2). (+)-Catechin has antibacterial properties, but (-)-catechin kills other plants with which it comes in contact. In the approximately 100 years since it was accidentally introduced to the United States, spotted knapweed has spread rapidly, replacing native plants over millions of acres and forcing grazing animals to search elsewhere for food. 

Spotted knapweed produces a phenolic compound that kills other plants. 

Blair, A.C. et al. (2006) A lack of evidence for an ecological role of the putative allelochemical (+/-)-catechin in spotted knapweed invasion success. JChem Ecol 32, 2327-2331... 

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. (2003) Intraspecific and interspecific interactions mediated by a phytotoxin (-)-catechin, secreted by the roots of Centauria maculosa (spotted knapweed). J. Chem. Ecol. 29,2397-2412... 

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