1. Herbicide Mode of Action

2. Classification by Mode of Action 1)Plant Growth Regulators 2)Amino Acid Biosysthesis Inhibitors 3)Lipid Biosynthesis Inhibitors 4)Cell Division Inhibitors 5)Photosynthesis Inhibitors 6)Cell Membrane Disrupters 7)Pigment Inhibitors

3. 1. Cell division inhibitor Microtuble formation inhibitors Mostly 2,6-Dinitroaniline derivatives

4. Chemical structures Benfluralin Trifluralin

5. Tubulin in cell organization Tubulin: , , ,  - etc…. Major function: –As a cytoskeleton –Polar coordination of chromosome

6. 2. Photosynthesis inhibitor Photosystem I inhibitor Photosystem II inhibitor In general photosynthesis can be classified with light- and dark reaction Light rxn: PS I and II: Targets of most herbicides Dark rxn: Calvin cycle: CO 2 fixation

7. Photosystem: General

9. Biological functions of Photosystems Protein Subunitsproton turn into form of ATP SubunitDescription PsaA PsaB PsaC PsaD PsaE PsaI PsaJ PsaK PsaL PsaM PsaX CytochromeCytochrome b 6 f complexSoluble proteinprotein FaFa In electron transport chain (ET C)electron transport chain FbFb In ETC FxFx FerredoxinElectron carrier in ETC PlastocyaninSoluble protein Lipids MGDG IIMonogalactosyldiglyceride lipid PG IPhosphatidylglycerolPhosphatidylglycerol phospholipidphospholipid PG IIIPhosphatidylglycerol phospholipid PG IVPhosphatidylglycerol phospholipid Pigments ChlorophyllChlorophyll a 90 pigment molecules in antenna systempigment Chlorophyll a5 pigment molecules in ETC Chlorophyll a 0 Early electron acceptor of modifie d chlorophyll in ETC Chlorophyll a'1 pigment molecule in ETC ß Carotene22 carotenoid pigment moleculescarotenoid Coenzymes/Cofactors MoleculeDescription Q K -A Early electron acceptor vitamin K 1 phylloquinone in ETCvitamin K 1 phylloquinone Q K -B Early electron acceptor vitamin K 1 phylloquinone in ETC FNR Ferredoxin-NADP + oxidoreductas e enzyme Ca 2+ CalciumCalcium ion Mg 2+ MagnesiumMagnesium ion

10. Biological function of each components Antenna Complex: chlorophyll and carotenoids mounted on two proteins: transmit the resonance energy from photons. Absorb all wavelengths of light within the visible spectrum. P700 Reaction Center: Modified chlorophyll(700nm), receives energy from antenna molecules and uses the energy from each photon to raise an electron to a higher energy level.

11. Phylloquinone A1: Phylloquinone A1 is the next early electron acceptor in PS I. vitamin K1. Iron-sulfur Complex: The reaction centers in this complex are secondary electron acceptors. Ferredoxin: Ferredoxin (Fd) is a soluble protein that facilitates reduction of NADP+ to NADPH.[ Ferredoxin-NADP+ Reductase (FNR): This enzyme transfers the electron from reduced ferredoxin to NADP+ to complete the reduction to NADPH.[ Plastocyanin: Plastocyanin then transfers the electron directly to the P700 reaction center in the PS I antenna complex.[4]

12. Photosystem II Major function: Extracting electrons from water The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol

13. General component in PS II Protein Subunits (only with known functio n) SubunitFunction D1 Reaction center Protein, bind s Chlorophyll P680, pheophyt in, beta-carotene,quinone and m anganese center D2Reaction center Protein CP43Binds manganese center CP47 PsbO Manganese Stabilizing Protei n Coenzymes/Cofactors MoleculeFunction ChlorophyllAbsorbs light Beta-Carotene quench excess photoexci tation energy HemeHeme b559 also Protoporphyrin IX co ntaining ironProtoporphyrin IX PheophytinPrimary electron acceptor Plastoquinone Mobile intra-thylakoid me mbrane electron carrier Manganese center also known as the oxyge n evolving center, or OEC

14. Reaction center of PS I

15. Simplified Image of PS II

16. Simplified model of photosynthetic system

17. Chemicals acting on PS PS I inhibitor: Bipyridylium

18. MOA of PS I inhibitor In light-exposed plants, it accepts electrons from photosystem I (more specifically Fd which is presented with electrons from PS I) and transfers them to molecular oxygen. In this manner, destructive reactive oxygen species are produced. In forming these reactive oxygen species, the oxidized form of paraquat is regenerated, and is again available to shunt electrons from photosystem I to start the cycle again. In natural PS I system, electron acceptor is NADP

19. Reactive Oxygen Species

20. Paraquat injured plant

21. PS II inhibitors Triazines Triazinones Benzothiadiazoles Nitriles Urea

22. Chemical structures Urea: N-Methyl and methoxyurea

23. Triazinones Benzothiadiazoles Nitriles

24. Triazines –Chlorotriazines –Methoxytriazines –Methylthiotriazines

25. Problems of triazine herbicides Act as endocrine disruptor Notable, especially with chlorotriazines React many basic residues or metabolites Form adduct with several biomolecules