SUBSTANTIAL HYDRAULIC SIGNALS ARE TRIGGERED BY LEAF-BITING INSECTS IN TOMATO

In various plants, defence responses can be induced throughout the shoot by localized damage or insect attack. Activation of such systemic defence responses must involve a rapid long-distance signal of wounding. There is firm evidence that, in the case of localized heat wounds, systemic signalling occurs by hydraulic dispersal of chemical elicitors. However, more natural wounds (such as those imposed by leaf-biting insects) may trigger only small hydraulic events, and it is not clear whether hydraulic dispersal could account for wound signalling in these cases. It is shown here that partial defoliation offers a method for amplifying wound-induced hydraulic events in tomato. Using this amplification, it is demonstrated that brief feeding by individual leaf-eating insects triggers substantial hydraulic events. The mass flows associated with these events are shown to be sufficient to drive hydraulic dispersal of elicitors through the tomato plant. It is concluded that hydraulic dispersal could be of major importance for wound signalling in plants in the natural environment.