Chapter 18: MOA Part 4 – Photosynthesis Inhibitors (PPO & Pigment Inhibitors)
18.9 Summary
This chapter explored four herbicide Sites of Action that interfere with photosynthesis in plants. The Cell Membrane Disruptors (PPO Inhibitors) reduce the formation of chlorophyll and also lead to the buildup of highly reactive singlet oxygen, which then destroys lipids and cell membranes. The Pigment Inhibitors also prevent the development of chlorophyll as well as the plant’s natural ability to dissipate reactive molecules created from biochemical processes and sunlight. Therefore, herbicides in this chapter and the next cause damage to plants by utilizing the power of the sun to create cellular harm.
Key Takeaways
Key takeaways from this chapter include:
- PPO Inhibitors belong to the Cell Membrane Disruptor Mode of Action (Group 14).
- PPO is an enzyme important to a biochemical pathway resulting in precursors to chlorophyll needed for photosynthesis.
- PPO Inhibitor herbicides lead to decreased chlorophyll and heme production, and the production of toxic levels of singlet oxygen which damage cell membranes.
- PPO Inhibitor damage results in necrotic lesions.
- Carotenoids can harvest light energy and transfer it to chlorophyll in the photosynthetic apparatus. Carotenoids also protect the photosynthetic apparatus by absorbing excessive energy and dissipate it as heat.
- Pigment inhibitors include herbicide groups 11, 12, 13, and 27.
- Pigment inhibitor herbicides result in bleaching of leaves from the destruction of chlorophyll.
- At the time this was published 4 weed species in the United States were resistant to pigment inhibitors.
- At the time this was published 4 weed species in the United States were resistant to PPO Inhibitors.