What is the Most Effective Jasmonates Form in Promoting Tomato and Maize Defense Responses to Spodoptera exiguaHerbivory?
Jasmonates proposed to have a prospective key role in the plant insect interaction. This study conducted to clarify the role played by JA and its derivatives in defense responses of tomato and maize to Spodoptera exigua infestation. Chlorophyll a/b ratio, soluble carbohydrates, proteins and amino acids content measured in infested plants and uninfested controls after 2 h, 2 days and 1 week of infestation. JA, MeJA and JA-L-Ile were quantified using HPLC-MS/MS under the same experimental conditions. The results show that S. exigua attack did not change Chl a/b ratio in tomato, while maize recorded a greater adaptability at the beginning of the infestation by decreasing Chl a/b ratio. Soluble carbohydrates content did not change in infested tomato leaves compared to control, while increased in infested maize at 2 h and 2 days. Free amino acids content reduced lower than control in tomato leaves at all observed time periods due to S. exigua attack, while in maize higher concentrations of free amino acids accumulated in infested plants after 2 h and 2 days. In both plants, S. exigua infestation induced JA, MeJA and JA-L-Ile to high levels at 2 h then, decreased gradually by increasing infestation time. JA concentration in infested maize was much higher than that in infested tomato leaves. However, MeJA and JA-L-Ile concentration in infested tomato leaves was higher than that in maize. In control plants, JA did not record, while MeJA recorded in comparable values both in tomato and maize. Therefore, JA assumed to play the main role in increasing defense responses to S. exigua. infestation as a direct signaling molecule, however MeJA could play an indirect role by inducing JA accumulation.