Conclusion:
Herbivory by S. exigua does not elicit ethylene pathway in
M. truncatula .
Induction of defense responses in M. truncatula against
caterpillar herbivory with intact spinneret is different from
caterpillar with impaired spinneret. Effectors in caterpillar labial
saliva could induce oxidative stress, induce the expression of
antagonistic SAR pathway and hence suppress the induction of TI in
M. truncatula . However, there was no difference in the expression
of the studied defense related genes in plants after herbivory by normal
or cauterized caterpillars.
An ethylene is a pleiotropic hormone involved in different physiological
and developmental processes (Wang et al., 2002). By comparing the
effects of herbivory with and without labial salivary secretion in wild
type M. truncatula verses ethylene insensitive, skl
mutant, we showed that ethylene could be involved in one response but
not in other after herbivory. Ethylene was involved in the suppressive
effect of defense protein due to normal caterpillar herbivory, it seemed
to regulate glutathione as well as accelerate the induction of oxidative
stress in plants. Ethylene had no role in the suppression of
MtRCA , a gene involved in primary metabolism, after caterpillar
herbivory but it is involved in suppression of regulatory genes,
MtRPK and MtRFP. It is also found that ethylene regulates
the expression of MtSTR in M. truncatula.