Influence Of Infestation By Herbivores With Different Feeding Habits Or Treatment By β-glucosidase On Levels Of Main Defense-related Signals In Rice Plants

Influence of infestation by herbivores with different feeding habits or treatment by β -glucosidase on levels of main defense-related signals inrice plantsUsing rice and three rice herbivores with different feeding habits, i.e. a phloem-feeding herbivore Nilaparvata lugens, a stembore(Chilo .suppressalia(Walker)) and a leaf folder(Cnaphalacrosis medinais (Gueene)), as a research system, the changes in levels of the main defense-related signals, jasmonic acid (JA), salicylic acid (SA), ethylene and hydrogen peroxide in rice plants after infestation by herbivores were investigated. Moreover, we also determined the effect of β-glucosidase, an elicitor from the saliva of N. lugens that plays an important role in the production of N. lugens-induced rice volatiles, on these signal concentrations in rice plants. The results are as follows:1) N. lugens infestation resulted in increases in SA, hydrogen peroxide and ethylene concentrations but not JA in rice plants, and detectable differences for SA, hydrogen peroxide and ethylene between herbivore-infested plants and non-manipulated plants started at 1.5, 1.5 and 2h after infestation respectively;C. medinais infestation increased levels of SA and hydrogen peroxide but not JA and ethylene, detectable differences starting at 0.5 and 24h after feeding respectively;C. suppressalia feeding enhanced the concentrations of SA, JA, ethylene and hydrogen peroxide, detectable differences starting at 8, 0.5, 0.5 and 2h after infestation respectively. This suggests that these herbivores with different habits can elicit a different set of signals in rice plants.2) There were obvious differences in levels of signals in different tissues of rice plants. The concentrations of SA and hydrogen peroxide are the highest in leaf sheaths, followed by leaves and the lowest is in stems. JA concentrations in leaves are higher than those in stems and leaf sheaths. The amount of ethylene released from whole plants was not influenced by herbivores with different habits that attacked different tissues of rice plants.3) Compared to control plants, wounding and treatment by P-glucosidase rapidly increased the levels of salicylic acid (SA), ethylene and H2O2 in plants: SA at 4 h after treatment, ethylene at 1.5-3 h after treatment, and H2O2 at 1 h after treatment. However, P-glucosidase elicitation did not increase jasmonic acid (JA) concentrations. The signaling components activated by P-glucosidase treatment are similar to those by N. lugens infestation, which may explain why both of the treatments have similar volatile profiles and equal attraction of the parasitoid.