Aging Effect to Accumulation of Lettucenin A in Lettuce after Elicitation with Various Abiotic Elicitors

A series of experiments were conducted to study the effect of age to accumulation of lettucenin A in lettuce (Lactuca sativa) after various elicitations. Lettuces were challenged with four different types of elicitation method; spray with silver nitrate (AgNO3) or copper sulfate (CuSO4), ultraviolet irradiation and freeze-thawed. Lettucenin A, a type of phytoalexin in lettuce accumulated with a higher concentration after challenged with chemical elicitors, silver nitrate (AgNO3) and copper sulfate (CuSO4). Physical elicitation with irradiation of short wavelength (254nm) ultraviolet radiation and freeze-thawed were also effective in eliciting the production of lettucenin A. However, the amounts were considerably lower compared to those elicited by chemical elicitors. Ultraviolet radiation and freeze-thawed stimulated lettuce to produce lettucenin A at a concentration of 1.52 µg/ml and 0.49 µg/ml respectively while AgNO3 and CuSO4 contributing to accumulation of 4.27 µg/ml and 4.26 µg/ml respectively. The elicitations of lettucenin A were both dependent on types of elicitor and the age of the plant. Treatments with AgNO3 and ultraviolet radiation both showed the same pattern production of lettucenin A. Lettucenin A accumulation increased significantly from week nine to the maximum at week twelve before it decreased to minimum at week eighteen. There is a week relation (R2= 0.69) between the accumulation of lettucenin A with the age of the lettuce with elicitation of silver nitrate. However, there is no relation with induction with ultraviolet radiation. Our results suggest lettuce produces the highest amount of lettucenin A after elicitation with chemical elicitors at twelve weeks old throughout the series of trial.