Identity, spatial distribution, and variability of induced chemical responses in tomato plants

Using four‐leaf tomato plants ( Lycopersicon esculentum Mill) as a model system, we examined the spatial distribution of damage‐induced changes in foliar protein activities. Terminal leaflets of third leaves of tomato plants were subjected to one of four types of damage, and the activities of four putative defenses – polyphenol oxidase, peroxidase, lipoxygenase, and proteinase inhibitors – were determined at four leaflet positions relative to the damaged leaflet. Multiple proteins were differentially induced by the different damage types. For a given damage type, the spatial pattern of induction was different for different proteins. More exhaustive spatial mapping of the polyphenol oxidase response to feeding by Helicoverpa zea Boddie revealed that damaged plants were more variable, both within and between plants, in the activity of this enzyme than undamaged plants. The spatial patterns of induction of these four putative defenses throughout the plant suggest that the induced plant is chemically heterogeneous and that different mechanisms of defense operate in different regions of the plant. These data are critical to an elucidation of cause‐effect relationships between induced chemicals and induced resistance in tomato foliage. In addition, these data suggest that induction functions, in part, to increase chemical variation in tomato plants; the potential role of phytochemical variation in plant defense is discussed.