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

Abstract

As a consequence of membrane lipid peroxidation, foliar defense compounds are changed by elevated ozone (O3), which in turn affects the palatability and performance of insect herbivores. The induced defense of two tomato [Solanum esculentum L. (Solanaceae)] genotypes, namely jasmonic acid (JA) pathway‐deficient mutant spr2 and its wild‐type control, was studied in response to cotton bollworm, Helicoverpa armigera Hübner (Lepidoptera: Noctuidae), as well as the digestive adaptation of these insects under elevated O3 in open‐top field chambers. Our data indicated that elevated O3 increased foliar JA and salicylic acid (SA) levels simultaneously and up‐regulated proteinase inhibitors (PIs) and lipoxidase activities in wild‐type plants, regardless of H. armigera infestation. In contrast, only the O3+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 O3. 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 O3 treatment. Increases in atmospheric O3 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.