INFLUENCE OF HERBIVORY-INDUCED COMPOUNDS ON CORN PLANT DIRECT DEFENSE

Abstract

Benzoxazinoids are common secondary metabolites in plants of the Poaceae family that act in plant defense. To evaluate the effect of herbivory induced plant volatiles (HIPVs) on the direct defense of maize production of benzoxazinoids in plants with and without herbivory of the stink bug Dichelops melacanthus was evaluated. The compounds: indole, (E)-2-hexenyl acetate, (Z)-3-hexenyl acetate, (R,S)-linalol, DMNT and (E)-β-farnesene were selected for this study. Healthy maize plants were exposed or not to individual compounds for 24 h. After this period, the exposition was interrupted, and plants were allowed to rest for one hour. After that each plant received or not virgin 5 D. melacanthus females and after 96h of herbivory the plants were submitted to a liquid-liquid extraction. The extracts obtained were analyzed by HPLC with UV detector and LC-MS. To evaluate whether plants subjected to volatiles had their direct defense activated, plants exposed or not to VPIHs were offered as food for D. melacanthus (males and females). The following parameters were measured: fertility, fecundity and survival of D. melacanthus. The indole and (Z)-3-hexenyl acetate induced the production of benzoxazinoids DIMBOA and HMBOAGlc, respectively. Plants that received the compounds (E)-2-hexenyl acetate, (E)-β-farnesene and DMNT showed suppression in the production of some benzoxazinoids, such as HMBOAGlc, DIMBOAGlc, DIMBOA and HDMBOAGlc, when compared to plants submitted only to herbivory. Insects fed on plants treated with such compounds, as well as indole, linalool and (Z)-3-hexenyl acetate, had reduced longevity, fecundity and fertility compared to insects fed on untreated maize plants. Induced plant defense covers a wide variety of mechanisms, in which case there has probably been some molecular change that has diminished insect feeding in plants treated with HIPVs. Further studies are been conducted to elucidate this hypothesis.