COLLABORATIVE RESEARCH: Coordinate Induction of Sink Strength and Polyphenol Metabolism in Trees

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The ability of plants to respond to damage by pests and pathogens is widespread, but not all plant tissues are capable of producing defensive responses. Defensive responsiveness is greatest in young leaves and decreases dramatically with age. The variation in defensive capabilities among different parts of plants affects the foraging of herbivores on plants, the ability of herbivores to develop resistance to plant defenses, and the success of predators in locating herbivores. To understand the ecology and evolution of plants and their interactions with herbivores, it is critical to understand how plant defensive responses differ among different plant tissues. The movement of carbohydrates throughout the canopies of trees may influence the ability of young foliage to develop defensive responses. For example, the ability of wounded Poplar leaves to obtain the resources they need to produce defensive chemicals (polyphenolics) appears to be affected by the rate at which carbohydrates are imported from the plant vascular system. In other words, the magnitude of the defensive response is directly related to the flow of resources to wounded leaves. This flow of resources causes variation in defensive responses among different plant tissues, because wounded tissues vary in their ability to acquire resources from the plant vascular system. The PIs propose to test this hypothesis rigorously with greenhouse and laboratory experiments on hybrid poplar and oak saplings. Chemical analyses of plant foliage will be conducted to assess defensive responses, and carbon 13 labeling experiments will be used to measure rates of resource movement in whole plants. The proposed research will result in (1) the development of a model designed to predict where and when defensive responses are likely to occur, (2) the establishment of monitoring technology that can be applied to a broad range of plant communities in the field, and (3) the training of graduate and undergraduate students in the plant sciences.