The signaling pathways that enable plants to mount defenses against
insect herbivores are known to be complex. It was previously demonstrated
that the insect-resistant maize (Zea mays L.) genotype Mp708 accumulates
a unique defense cysteine proteinase, Mirl-CP, in response to caterpillar
feeding. In this study, the role of ethylene in insect defense in
Mp708 and an insect-susceptible line Tx601 was explored. Ethylene
synthesis was blocked with either cobalt chloride or aminoethoxyvinylglycine.
Alternatively, ethylene perception was inhibited with 1-methylcyclopropene.
Blocking ethylene synthesis and perception resulted in Mp708 plants
that were more susceptible to caterpillar feeding. In addition, fall
armyworm (Spodoptera frugiperda) larvae that fed on inhibitor-treated
Mp708 plants had signifycantly higher growth rates than those reared
on untreated plants. In contrast, these responses were not significantly
altered in Tx601. The ethylene synthesis and perception inhibitors
also reduced the accumulation of Mirl-CP and its transcript mir1
in response to herbivory. These results indicate that ethylene is
a component of the signal transduction pathway leading to defense
against insect herbivory in the resistant genotype Mp708.
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