Plant defensive mechanisms against insect pests

Sammanfattning: This study has focused on testing the following two hypotheses:• Pest resistant plants have higher levels and/or several different kinds of secondary metabolites. • Induced defensive systems in resistant plants are activated more rapidly than those of susceptible plants. As a background for the test of the hypotheses a short literature study was performed concerning plant defensive mechanisms in Arabidopsis thaliana. This survey describes basic defenses like trichomes, constitutive defenses like the glucosinolate-myrosinase system, which can create toxins, and inducible defenses like the JA-, ET- and SA- defenses, which result in different chemical responses. Feeding experiments with the plant A. thaliana, the generalist insect pest Spodoptera littoralis and the specialist insect pest Plutella xylostella have been conducted. The results showed that the Spodoptera generalist is greatly affected by the plant`s defensive system, while the Plutella insect is not. A qPCR analysis of LOX 2 gene expression was conducted to examine the defensive strategy of plants against attacks by Plutella, which showed that all plants except one activated their inducible defenses. A feeding experiment with primed (Bacillus amyloliquefaciens) Arabidopsis plants and Spodoptera larvae was conducted and showed that primed plants, which trigger their defenses faster, not necessarily counteract pests better than non-primed plants.