Abstract
ABSTRACTThe biochemical and molecular basis of the defense in a mild tolerant (ICPL-332) and susceptible (ICPL-87) cultivars of pigeon pea (Cajanus cajan) due to Helicoverpa. armigera infestation was studied. We found that feeding by the larvae generated H2O2 in a localized manner and activity was observed upto 12 h (hrs) of with a sharp decline within 24 h. Similarly, PPO activity was also detected till 12 h of treatment, which decreased after 24 h of feeding by larvae. The activity of trypsin inhibitor was detected in all the treatments when assayed at 12 and 24 h after larval feeding. The expression of defense genes like the Pre-hevein-like protein PR-4 precursor (PR-4), protease inhibitor/seed storage/LTP family protein (Ltp) were significantly up-regulated in ICPL-332 upon infestation after 12 h as compared to ICPL-87, whereas the endo 1, 4 -β-glucanase (Kor-1) gene was expressed in both the cultivars after 24 h of infestation. Both the cultivars varied with respect to the induction of defense-related genes during larval feeding, both the PR-4 and Ltp genes appeared to be important for defense against H. armigera in pigeon pea. Thus, the present study revealed an insight of herbivore-induced biochemical and molecular changes in pigeon pea.
Highlights
Plants trigger the induction of defense mechanisms in response to the damage caused by insect feeding which are categorized as direct and indirect defense (Karban and Baldwin 1997; Thomma et al 1998; Kessler and Baldwin 2002)
The induction of defense response upon H. armigera infestation and exposure to the signaling molecules in pigeon pea was assayed by detection of H2O2, polyphenol oxidase activity (PPO), the amylase inhibitor (AI) and trypsin inhibitor (TI) expression after 12 and 24 h of treatments
When H2O2 accumulation was compared among the samples, the accumulation was found to be maximum in H. armigera infested leaves of ICPL-332
Summary
Plants trigger the induction of defense mechanisms in response to the damage caused by insect feeding which are categorized as direct and indirect defense (Karban and Baldwin 1997; Thomma et al 1998; Kessler and Baldwin 2002). The major signaling molecules that regulate the defense mechanisms are jasmonic acid (JA), salicylic acid (SA) and ethylene (ET) (Koornneef and Pieterse 2008) These hormones either act individually or are involved in complex cross talks networks, which finely tune the defensive response (Verhage et al 2010; War et al 2012). Plants respond differently to insect injury and mechanical wounding (Korth and Dixon 1997; Reymond et al 2000) This difference may be because of the presence of several insect-specific elicitors in oral secretions of a herbivore (Mattiacci et al 1995). The elicitor molecules in the oral secretion include various fatty acid conjugate, enzymes, and other complex molecules, which are known to generate a defensive response in plants (Mattiacci et al 1995; Alborn et al 1997; Funk 2001; Halitschke et al 2001)
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