Phenylpropanoid Pathway for Lignin Biosynthesis and Protein Defensive Strategy against Melon Fly

Many plant lectins expressed in fruits are known to possess defensive mechanism larvicidal functions. Plants respond to herbivory through various morphological, biochemical, and molecular level mechanisms to resist the effects of herbivore insect attack. The defensive compounds are either produced constitutively or in response to plant damage, and affect feeding, growth, and survival of herbivores. Present studies aimed to compare the lectin protein expression in selected cucurbit fruits to understand the resistance and susceptibility against melon fly infestation. Both susceptible (bitter gourd, snake gourd and cucumber) and resistant (chayote and bottle gourd) fruit latex sap were prepared and lectin proteins were characterized by hemo and leuco agglutination activity. Some are partially purified to identify glycocode as N-acetyl glucosamine and stability was assessed for proteases, pH and temperature. The larval growth was inhibited that are fed at low concentrations and were found dead at high concentration after incubation for about 24 hr. The histopathology indicates the lectin-induced damage to the larval gut region, indicating lectin-induced toxicity. The lectin protein induces toxicity by binding and inducing digestive impairment in larvae growth and causing mortality. The comparative observations indicate that lectin protein expressed from the fruit tissues of chayote and bottle gourd secretes latex and defends the melon fly larval infestation and provides resistance. Present investigation describe for the content of lignin in the tissue of healthy and infected cucurbit fruits which may provide the evidence for their resistance and susceptibility against melon fly infestation. If the monolignol levels or polymerized lignin units are high due to increased level of PPP (Phenylpropanoid Pathway) enzymes, this will harden the cells and make the larvae hard to break cell wall to feed on those tissues.