Salt addition over short and long durations does not prime plants for an increased-induced PPO and TPI response to insect herbivory
There was no significant interaction between salt and herbivory on PPO and TPI levels at all time intervals (all P > 0.05). Furthermore, salt application had no effect on PPO and TPI levels, regardless of insect herbivory (all P > 0.05). Herbivory, however, led to a significant increase in the PPO activity and TPI levels, regardless of salt application (Figure 8A : PPO;Figure 8B : TPI; all P < 0.05). There were no significant increases in PPO levels after herbivory at 7 days of salt treatment (P > 0.05). Salt addition over short and long durations did not prime tomato plants for a faster-induced response in terms of PPO and TPI levels to insect herbivory.
Na+ ions accumulate in tomato plants upon salt treatment
Salt treatment of leaves led to increased leaf Na+content in a dose-dependent manner (Figure 9; F(2, 15) = 262.2, P < 0.0001). The Na+ content in leaves was 786.8 ± 63.83 mg/kg in 0 mM treated leaves, 6575 ± 358.3 mg/kg in 100 mM leaves, and 10497 ± 374.8 mg/kg in 200 mM treated leaves.