Since plant defense signaling mechanisms may well be selected to respond as rapidly as possible to the presence of herbivores, their initial response is probably modu lated by physiological means in the first instance, rather than by changes in expression levels. To confirm this selleckchem hy pothesis further studies are needed to measure the levels and activities of terpenoid biosynthetic enzymes partici pating in volatile formation. Transcripts were induced encoding other protein types In addition to transcripts for proteins known to be involved in defense responses, we found enhanced tran script abundances of proteins in egg induced plants for which little knowledge is available on their possible role in defense responses towards in sect eggs.

These proteins are assigned to general func tions, such as stress response, protein metabolism, signaling and transport. They probably represent a crit ical link between defense and developmental processes in these plants. Next to the up regulation of lipoxygen ase especially high EST numbers and a strong significant difference between the treatments were found for tran scripts associated with sieve element occluding proteins, which supposedly play a role under stress conditions after insect attack. Among the enhanced transcript abundances in egg induced plants high EST numbers were found for transcripts of catalases, which protect cells from the toxic effects of reactive oxygen species such as hydrogen peroxide, which are often found in stressed tissues.

Herbivory has been found to elicit the production of ROS that are involved in further downstream transduction cascades, leading to the induc tion of defense response genes, as well as in loca lized cell death. We hypothesize that enhanced ROS levels caused by injury during egg laying are most likely responsible for the increased expression of related classes of catalases in elm, where localized cell death has been observed under the egg clutches. Interestingly high EST numbers of trancripts associated with methionine metabolism were found in egg induced plants. An increase of methionine synthase after MeJA treatment was also reported for A. thaliana. The pro teinogenic amino acid L methionine has many essential direct and indirect functions in cellular metabolism, in cluding ethylene biosynthesis, as well as the biosyn thesis of defense compounds. High EST numbers were also found for transcripts involved in protein folding and degradation, pos sibly indicating that turning over and re configuring the proteome might be a critical step in the defensive responses of plants, as Anacetrapib well possibly having an important role in signal transduction, including the fine tuning of JA signaling.