Defense protein responses of white and green ash to wounding and emerald ash borer homogenates.
Barto, Eusondia*,1, Herms, Dan 2, Bonello, Pierluigi2, Cipollini, Don1, 1 Wright State University, Dayton, OH, USA2 The Ohio State University, Columbus, OH, USA
ABSTRACT- Emerald Ash Borers (EABs) have infested Canada and parts of Michigan and Ohio, killing ash trees as they go. They are originally from Asia, where they only feed on sickened ash trees. In North America they are able to feed on healthy ash trees, which may relate to levels of constitutive and inducible defense chemicals around wounded sites. We studied the production of defense proteins through time in response to mechanical wounding and EAB homogenates in the phloem of mature white and green ashes grown in a common garden in Ohio. On each tree, wounds were created with a boring tool and wounds were treated with EAB homogenate or water. These samples were compared to an unwounded control site on each tree. Activities of trypsin inhibitor, polyphenoloxidase, peroxidase, chitinase, beta-glucosidase, and total protein content were compared among treatments through time. For green ash, both trypsin inhibitor and chitinase activities responded significantly to wounding and varied through time. Total protein content of the phloem also increased in response to wounding and varied through time. For white ash, both trypsin inhibitor and chitinase also responded significantly to wounding and varied through time, but no effects were seen in any other protein measure. We found some evidence for induction of defense proteins in wounded phloem of native ashes, although several proteins failed to respond to wounding. This modest response to wounding may explain why native North American ash trees are quite susceptible to EAB attack.
Key words: emerald ash borer, defense proteins, inducible defenses
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