When plants are attacked by leaf-chewing herbivores, they must cope with the loss of leaf tissues, which hold an abundance of the plant's nutrients and are important for capturing energy from sunlight for growth. Plants can store some of their energy and nutrients in tougher tissues, such as stems and roots that many herbivores cannot eat as readily. Starch and proteins are the most common storage compounds in plants. The use of radioactive carbon in recent research has allowed the study of allocation processes in living plants. One such study indicates that plants might increase storage in response to herbivory. An important signal molecule, jasmonic acid (JA), involved in plant recognition of herbivore attack increased the amount of radioactive carbon transported to the lower stem and roots in poplar and aspen tree saplings. The research proposed here will determine whether JA and insect herbivory cause increases in storage compounds in the stem and roots and increased nutrient intake by the roots of poplars and aspens. Short-term processes will be studied in living plants using radioactive isotopes of elements important to plants (carbon-11, nitrogen-13). The longer-term build-up of storage compounds will be examined using stable isotopes (carbon-13, nitrogen-15) and chemical analysis. Increased nitrogen uptake and increased build-up of carbon and nitrogen storage compounds following the initiation of herbivore leaf-chewing would indicate that plants can adjust their metabolism to maximize their ability to survive leaf loss and damage and to improve their re-growth. This pioneering research of storage regulation in response to herbivore signals will be necessary to understand how plants have evolved to cope with herbivory. Moreover, an improved understanding of how plants tolerate damage may influence commercial agricultural and forestry practices, and could generate insights for manipulating plants to improve survival and growth.
