Abstract

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

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