Plants often respond to attack by pests and pathogens by activating complex defense responses, which include the production of toxic or deterrent chemicals. However, all plant tissues are not equally responsive to attack. In nature the distribution of plant defenses, which provide pest and pathogen resistance and enhance harvest quality, is uneven and notoriously difficult to predict. Recently, a critical first step in the activation of defense responses was discovered. In poplar trees, it was shown that wounded tissues must import resources, in this case sugars, via the plant vascular system to support the production of defensive substances. In these trees, wounded tissues alter their metabolism, becoming stronger "sugar sinks" and drawing resources away from elsewhere in the plant. As a result, stronger sugar sinks have stronger defense responses which disappear whenever the flow of sugars is interrupted. This observation helps to explain why plant defenses are unevenly distributed in nature. It also suggests several strategies for manipulating levels of plant products, including those from agriculturally-important species. This project would determine if wounding boosts the "sugar sink" strength of other plant species and types, including herbs and vines producing a wide variety of defensive substances such as tannins, alkaloids, proteins, and glucosinolates. The project involves large-scale experiments to test the hypothesis that many different plants shift the long-distance flow of sugars and other resources in response to attack. It will also examine factors that would disrupt sugar flow in nature, such as the development of flowers and fruits which out-compete wounded tissues for sugar resources or the simultaneous attack by multiple insects or pathogens.
BROADER IMPACTS
Results of these studies will provide insight into factors that influence pest resistance of plants and may be manipulated to enhance crop or tree productivity. The strategies plants use to manipulate sugar flow are important in agriculture, since they determine both the timing and quality of production and harvest. The mechanisms studied are also central to carbon sequestration and release by plants and may impinge on the global carbon budget. Results should determine whether trees like poplar can be altered to sequester additional carbon belowground. The project will engage a substantial number of undergraduates from two contrasting (large/small) institutions in interdisciplinary, collaborative research and outreach (including K-12 schools).
