Objective Stress responses of the insect-resistant and susceptible rice germplasms to brown planthopper (BPH) were compared to decipher the underlining mechanism for better control on one of the major pests on rice.

Method BPHs were allowed to feed on the insect-resistant BP4 and insect-susceptible TN1 rice plants. Phenotypic changes on the plants of two contrasting varieties of rice were observed. In addition, contents of malonaldehyde, proline, hydrogen peroxide, and total flavonoids as well as activities of catalase (CAT), peroxisome (POD), superoxide dismutase (SOD), ascorbate peroxidase (APX), and glutathione reductase (GR) of the plants were monitored by biochemical methods, those of plant hormones, including abscisic acid, jasmonic acid, auxin, and salicylic acid, measured by ELISA and HPLC, and expressions of the genes associated with antioxidant enzymes and salicylic acid signal transduction and synthesis analyzed by RT-qPCR.

Result Six days after infestation by BPHs, all TN1 seedlings died but BP4 had a mortality rate of merely 11.11% with a rated Level 3 resistance to the pest. In 4 d after the exposure, both germplasms had significantly increased contents of malonaldehyde and proline without any changes on the total flavonoids; TN1, but not BP4, rose significantly on hydrogen peroxide; TN1 increased significantly on the activities of CAT, POD, and SOD, but BP4 decreased significantly; neither germplasms changed on APX activity; TN1, but not BP4, declined significantly on GR activity; and only BP4 increased significantly on the content of salicylic acid. In 2 d post-introduction, the expressions of most antioxidant enzyme-associated genes in BP4 were downregulated but upregulated in TN1. Meanwhile, the expressions of the genes related to the salicylic acid signal transduction and synthesis in BP4 were upregulated.

Conclusion BPH infestation induced significant differentiations between the resistant BP4 and the susceptible TN1 rice germplasms in response to the stress with respect to the contents of hydrogen peroxide and salicylic acid as well as the antioxidant enzyme activity of the plants.