Evaluating ascorbate oxidase as a plant defense against leaf-chewing insects using transgenic poplar

Area of Science:

• Plant biology
• Insect physiology
• Biochemistry

Background:

• Ascorbate (vitamin C) is a vital antioxidant and nutrient for insect herbivores.
• Ascorbate oxidase (AO) in plants may reduce ascorbate availability, acting as a defense mechanism.
• Investigating AO's role in plant-insect interactions is crucial for understanding herbivory.

Purpose of the Study:

• To test the hypothesis that elevated foliar ascorbate oxidase (AO) in poplar deters insect herbivores.
• To investigate the biochemical mechanisms of ingested AO activity within insect guts.
• To assess the impact of AO overexpression on insect performance and nutritional indices.

Main Methods:

• Generated transgenic poplar with significantly higher foliar AO activity.
• Fed leaves from transgenic and control poplar to Lymantria dispar (caterpillars) and Melanoplus sanguinipes (grasshoppers).
• Measured ascorbate and ascorbyl radical levels in insect gut contents; conducted insect performance bioassays.

Main Results:

• No significant changes in ascorbate or ascorbyl radical levels were detected in the gut contents of either insect species when feeding on AO-overexpressing poplar.
• Commercial AO treatment of control leaves also failed to alter midgut biochemistry in L. dispar.
• Insect performance metrics (growth rate, consumption rate, nutritional indices) showed no significant differences between treatments.

Conclusions:

• Elevated poplar AO is unlikely to function as an effective defense against tested herbivores.
• Low oxygen levels within the guts of these insects likely inactivate ingested AO.
• Further research may explore alternative plant defense strategies against insect herbivores.