Summary for Herbicides that Act Through Photosynthesis

The majority of available herbicides interact with a plant cell in a manner that causes damage from the energy in sunlight. Herbicides that inhibit the normal production of protoporphyrin IX, a photosensitizing molecule, cause severe photodynamic damage. Herbicides that inhibit biosynthesis of carotenoids deprive plant cells of the photoprotection given by these molecules, permitting damage from chlorophyll mediated photosensitization. Inhibitors of electron transfer from Photosystem II block photophosphorylation and starve the cell of the energy normally produced by photosynthesis. And finally, some herbicides act by diverting high-energy electrons from Photosystem I to generate damaging superoxide and other free radicals. Although each of these four classes of herbicides has a distinct mode of action, each interferes with the plant's ability to safely handle the high energy present in sunlight.