Caterpillar with intact spinneret induces oxidative response in
plants
The level of total, reduced, and oxidized forms of ascorbate and
glutathione was measured in M. truncatula leaves at 15, 30 and 45
minutes after herbivory by caterpillars with intact or cauterized
caterpillars in wild type, jemolong A17. There was no significant
increase in the total ascorbate and total glutathione in both genotypes
until 45 minutes of herbivory. However, although both caterpillar
feedings showed no significant changes in oxidized as well as reduced
form of ascorbate, caterpillar with intact spinneret significantly
increased the ratio of oxidized to reduced form of ascorbate at 45
minute. As caterpillar without labial salivary secretion caused no
significant difference in the ratio of oxidized to reduced ascorbate, it
indicates that the effectors in labial saliva creates oxidative
environment in the wounded tissues.
Similar to reduced ascorbate, the level of reduced glutathione was not
changed due to herbivory with or without labial salivary secretion at
any time point. However, normal caterpillar accumulated significantly
higher level of oxidized glutathione (GSSG) than control and cauterized
caterpillar after 15 and 30 minutes of herbivory. At 45 minute, the
level of GSSG was reduced to constitutive level. Higher level of GSSG
due normal caterpillar herbivory and thus the increased ratio of
oxidized to reduced glutathione confirmed the labial salivary-specific
induction of oxidative stress in caterpillar fed plants. Together with
this and a trend of decreasing concentration of reduced ascorbate
(although not significant) after 15 min of herbivory by normal
caterpillar reveals the activation of ascorbate-glutathione cycle in
wounded tissues after normal caterpillar herbivory.