Defensive responses in Capsicum annuum (L) plants, induced due to the feeding by different larval instars of Spodoptera litura (F)

A study was conducted to demonstrate the induced defence responses of chilli plants against herbivory by different larval instars of the tobacco cutworm, Spodoptera litura (F) at different intervals of time (0, 24, 48 and 72 h) after feeding. The rate of various antioxidative enzymes such as peroxidase, catalase (CAT), superoxide and polyphenol oxidases generated in chilli, Capsicum annuum (L) plant leaves due to damage caused by different larval stages of S. litura, and the primary and secondary metabolite contents were quantified. Also, lipid peroxidation content in plant leaves was measured by a malondialdehyde method, while the photosynthetic pigment concentrations were estimated spectrophotometrically. Early instar larval feeding caused an enhanced production of reactive oxygen species (ROS) compared with the older instars. Not much variation occurred in the primary metabolite content of plants fed upon by herbivores, and normal chilly plants. However, a considerable increase in the activities of CAT and superoxide dismutase was recorded after 24 h of insect feeding. Hydrogen peroxide accumulation was higher in plants fed by 2nd instar larvae when estimated after 0 h (immediately after 2 h of feeding was completed), whereas no hydrogen peroxide accumulation was observed due to the feeding by 5th instar larvae using the 3,3'-diaminobenzidine (DAB) staining method. Nitro blue tetrazolium staining for the location of superoxide ions revealed the immediate accumulation of superoxide ions at the damaged site due to the feeding by all the tested instar larvae of S. litura. Among the different larval stages tested, 2nd and 3rd instar feeding led to more superoxide radical accumulation as an indication of ROS generated as a counteraction to herbivory.