Lettucenin A and Its Role against Xanthomonas Campestris

Lettucenin A is the major phytoalexin produced in lettuce after being elicited by biotic or abiotic elicitors. Theproduction of lettucenin A in leaf can be induced by 5% of CuSO4 and 1% of AgNO3. A clear inhibition zone where thefungi Aspergillus niger failed to develop on TLC plates dipped in hexane- ethyl acetate (1-1, v/v) at Rf 0.45 wasobserved. Lettucenin A was detected at a retention time of approximately 5.3 min after being injected into the HPLCrun with isocratic solvent system containing water- acetonitrile ratio 60-40, (v/v). In vitro antibacterial study withXanthomonas campestris results showed this pathogen has different sensitivity to all tested concentrations of lettuceninA. The bacteria was more sensitive to higher concentration of lettucenin A (333, 533 and 667 g ml-1), compare tolower concentrations such as 67 g ml-1. Thus, the relationship between the bacteria growth rate and lettucenin Aconcentration was negatively correlated. However, the bacteria growth rate continues to increase after two hours ofincubation. Hence, it is suggested that X. campestris may have the ability to detoxify lettucenin A. The success orfailure of X. campestris to invade lettuce may very well depend on the balance between accumulation and degradationof lettucenin A at the invading sites of lettuce. In summary, lettucenin A may play an important role in the resistance oflettuce against microbial colonization.