Elevated ozone induces jasmonic acid defense of tomato plants and reduces midgut proteinase activity in H elicoverpa armigera

As a consequence of membrane lipid peroxidation, foliar defense compounds are changed by elevated ozone (O 3 ), which in turn affects the palatability and performance of insect herbivores. The induced defense of two tomato [ S olanum esculentum L. ( S olanaceae)] genotypes, namely jasmonic acid ( JA ) pathway‐deficient mutant spr2 and its wild‐type control, was studied in response to cotton bollworm, H elicoverpa armigera H übner ( L epidoptera: N octuidae), as well as the digestive adaptation of these insects under elevated O 3 in open‐top field chambers. Our data indicated that elevated O 3 increased foliar JA and salicylic acid ( SA ) levels simultaneously and up‐regulated proteinase inhibitors ( PI s) and lipoxidase activities in wild‐type plants, regardless of H . armigera infestation. In contrast, only the O 3 + H . armigera treatment increased free SA levels in spr2 plants, but did not affect JA level or PI activities. Additionally, the lower activity of midgut digestive enzymes, including active alkaline trypsin‐like enzyme and chymotrypsin‐like enzyme, was observed in the midgut of cotton bollworms after they consumed wild‐type plants treated for 2 h with elevated O 3 . With temporary increases at 8 h, all four digestive enzymes of interest in the insect midgut dropped when they were fed with wild‐type plants under elevated O 3 treatment. Increases in atmospheric O 3 are thought to increase JA signaling and consequently reduce the activities of midgut digestive enzymes in H . armigera , therefore enhancing plant resistance against insect herbivores.