DROUGHT LIMITS INDUCED TWINING BY LEAF DAMAGE IN THE CLIMBING PLANT IPOMOEA PURPUREA (L.) ROTH (CONVOLVULACEAE)

Abstract

The environment may limit the expression of induced responses to herbivory, such as increased chemical or physical defenses. Recent studies in climbing plants have shown that leaf damage induces twining. This response may confer protection against ground herbivores in the field. We addressed the effect of drought on the induced twining of the annual vine Ipomoea purpurea (Convolvulaceae), which can experience drought stress in natural conditions. In a greenhouse experiment, we recorded twining rate (proportion of plants successfully climbing at a given time) of damaged and undamaged individuals of I. purpurea subjected to control watering and water shortage treatments. We also estimated stem growth rate and stem water content in experimental plants, just after the evaluation of climbing success. Plants in the drought treatment showed reduced twining induction by leaf damage compared to control plants. Neither stem growth nor stem water content were affected by leaf damage or drought. Results suggest that drought constrains the induced twining through mechanisms not directly related to stem growth and water content. It is suggested that drought might trigger signals that counteract those elicited by leaf damage. The induced twining may be an advantage in the presence of ground herbivores, but the environmental susceptibility of this response may limit its ecological significance.