Mechanical leaf damage causes localized, but not systemic, changes in leaf movement behavior of the Sensitive Plant, Mimosa pudica (Fabaceae) L.

Abstract

A small number of species, including Mimosa pudica, use rapid leaf movement as a presumptive defensive strategy. How movement-based defenses change in response to mechanical damage and whether changes are localized or systemic is unknown. This is in contrast to a substantial literature describing how mechanical leaf damage can cause morphological and chemical responses within a diversity of plant species. Depending on the species and the stimuli, these chemical and morphological responses can be localized to the tissues damaged or systemic throughout the plant body. Here we report the results of a small experiment designed to test the following: (i) whether mechanical leaf damage influences subsequent leaf closure behavior, and (ii) whether changes were systemic or localized. To do this, we scored leaves using a behavioral assay (time-to-reopen leaves following a subsequent touch stimuli) for several days before and following mechanical damage. Leaves above and below the damaged leaf were observed, on damaged and undamaged plants, allowing us to assess whether any change was systemic. We found leaf damage caused strong localized effects, greatly increasing the time-to-reopen of the damaged, but not adjacent, leaves. Neither the physiological cause nor fitness consequences of this behavioral shift are known. Interestingly, this altered behavior resulted in damaged leaves remaining “hidden” longer than undamaged leaves. If leaf closure reduces risk of herbivory, there could be adaptive value, analogous to inducible chemical and morphological defenses.