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Protoporphyrinogen Oxidase-Inhibiting Herbicides

Published online by Cambridge University Press:  12 June 2017

Stephen O. Duke
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776
John Lydon
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776
José M. Becerril
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776
Timothy D. Sherman
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776
Larry P. Lehnen Jr.
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776
Hiroshi Matsumoto
Affiliation:
USDA, Agric. Res. Serv., Southern Weed Sci. Lab., P.O. Box 350, Stoneville, MS 38776

Abstract

Several commercial and experimental herbicides such as p-nitrodiphenyl ethers, oxadiazoles, and cyclic imides inhibit protoporphyrinogen IX oxidase (Protox), the enzyme that converts protoporphyrinogen IX to protoporphyrin IX (Proto). This leads to uncontrolled autooxidation of the substrate and results in accumulation of Proto. Blockage of the porphyrin pathway at this site inhibits synthesis of both chlorophylls and heme. Heme is a feedback regulator of the porphyrin pathway. Thus, inhibition of Protox also deregulates the pathway, causing increased carbon flow to the accumulating pool of Proto. Proto is a potent photosensitizer that generates high levels of singlet oxygen in the presence of molecular oxygen and light. In plants treated with these herbicides, damage is light dependent and closely correlated with the level of Proto that accumulates. Proto accumulation is apparently largely extraplastidic, resulting in rapid photodynamic damage to the plasmalemma and tonoplast. After high levels of Proto accumulate in response to these herbicides, protochlorophyllide (PChlide) levels can increase also; however, Proto appears to be the primary photodynamic pigment responsible for the herbicidal activity.

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Type
Special Topics
Copyright
Copyright © 1991 by the Weed Science Society of America 

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