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Title: Abscisic acid and water stress as mediators of root herbivore-induced leaf resistance

Author
item ERB, MATTHIAS - University Of Neuchatel
item KOLLNER, TOBIAS - Martin Luther University
item DEGENHARDT, JORG - Martin Luther University
item ZWAHLEN, CLAUDIA - University Of Neuchatel
item Hibbard, Bruce
item TURLINGS, TED - University Of Neuchatel

Submitted to: New Phytologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/26/2010
Publication Date: 10/15/2010
Citation: Erb, M., Kollner, T., Degenhardt, J., Zwahlen, C., Hibbard, B.E., Turlings, T.C. 2010. Abscisic acid and water stress as mediators of root herbivore-induced leaf resistance. New Phytologist. 189:308-320.

Interpretive Summary: Systemically induced resistance is common and important in plant-pathogen and plant-insect interactions. The mechanisms triggered by microorganisms and leaf-herbivores that lead to systemic resistance are largely understood, but, as yet, it remains unknown how root herbivory may increase resistance in the above ground part of plants. To resolve this we investigated the systemic resistance induced by the western corn rootworm, a root herbivore of corn, against herbivores on the leaves of corn. Plants infested with western corn rootwrom suffered less above ground herbivory in the field and showed reduced growth in the laboratory. Root herbivory did not lead to a classical systemic wound-induced response in the leaves, but triggered water loss and abscisic acid accumulation. By chemically and genetically inhibiting abscisic acid synthesis in plant, we show that the induction of abscisic acid by itself is partially responsible for the induction of defense genes. In addition, the leaf herbivore was sensitive to changes in the plant’s water balance induced by root herbivory. We conclude that the apparent increase in leaf resistance after root feeding by western corn rootworm is the result of an upset water balance, which results in systemic hydraulic changes and reduced host-suitability of the leaves for chewing herbivores. A thorough understanding of this phenomena could lead to the development of new management tools for insect pests.

Technical Abstract: Systemically induced resistance is a common and important phenomenon in plant-pathogen and plant-insect interactions. The mechanisms triggered by microorganisms and leaf-herbivores that lead to systemic resistance are largely understood, but, as yet, it remains unknown how root herbivory may increase resistance in the above ground part of plants. To resolve this we investigated the systemic resistance induced by the root herbivore Diabrotica virgifera virgifera against lepidopteran herbivores in the leaves of Zea mays. D. virgifera infested plants suffered less above ground herbivory in the field and showed reduced growth of Spodoptera littoralis caterpillars in the laboratory. Root herbivory did not lead to a classical systemic wound-induced response in the leaves, but specifically triggered water loss and abscisic acid (ABA) accumulation. By chemically and genetically inhibiting ABA-biosynthesis, we show that the induction of ABA by itself is partially responsible for the induction of defense genes, but not for the early resistance against S. littoralis. Instead, the herbivore is sensitive to changes in the plant’s water balance induced by root herbivory. These changes are most pronounced under low water supply and when D. virgifera is allowed to feed on the upper root system, which was found to be the feeding side that is optimal for the development of the root herbivore. We conclude that the apparent increase in leaf resistance after root feeding by D. virgifera is the result of an upset water balance, which results in systemic hydraulic changes and reduced host-suitability of the leaves for chewing herbivores.