Vascular architecture generates fine scale variation in systemic inductionof proteinase inhibitors in tomato

Systemic induction following damage has been found in many plant species. D espite this widespread appreciation for the importance of induction, few st udies have characterized the spatial variability of induction. We used toma to, Lycopersicon esculentum, to examine how damage to a single leaf affecte d the spatial distribution of systemic induction of proteinase inhibition i n leaves above the damaged leaf. We crushed each leaflet of the second true leaf with forceps and measured the spatial distribution of proteinase inhi bition in leaves 3, 4, and 5 at 8, 16, 24, 48, 72, and 120 hr. Constitutive levels of proteinase inhibitor activity were quantified in undamaged plant s. We hypothesized that, due to vascular control of signal movement, system ic induction would show both among and within leaf variability. Following d amage to leaf 2, induction was most pronounced in leaf 5 and minimal in lea f 3. In general, proteinase inhibitor activity was greatest at 24 hr and th en declined. As predicted by vascular architecture, the near side of leaves in adjacent orthostichies showed higher induction than the far side of lea ves. There was no increase in proteinase inhibitor activity in the undamage d neighboring plants. Overall our results demonstrate that systemic inducti on of proteinase inhibitors is partially controlled by vascular architectur e and that future studies on systemic induction should examine the vascular architecture of the plants being studied. We argue that this spatial varia tion may influence the performance of herbivores sensitive to induced chemi cal changes.