Plant Physiol. Drug Metab Dispos
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Plant Physiology 64:774-779 (1979)
© 1979 American Society of Plant Biologists

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Articles

A Mechanism of Chlorosis Caused by 1,3-Dimethyl-4-(2,4-dichlorobenzoyl)-5-hydroxypyrazole, a Herbicidal Compound 1

Katsuhiko Kawakuboa,2 and Masahiro Shindoa

Takuo Konotsuneb

a Agricultural Chemicals Research Laboratories, Sankyo Co., Ltd., 1041 Yasu, Yasu, Shiga, Japan, b Agricultural Chemicals Research Laboratories, Sankyo Co., Ltd., 1-2-58 Hiromachi, Shinagawa, Tokyo, Japan

In organic solvents, 1,3-dimethyl-4-(2,4-dichlorobenzoyl)-5-hydroxypyrazole (DTP) converted chlorophyll a and b extracted from rice seedlings (Oryza sativa L. `Kinmaze') into pheophytin a and b, respectively. On comparing the chlorophyll-converting activity of DTP to those of acetic, glycolic, 2,4-dichlorobenzoic, monochloroacetic, 2,6-dichlorobenzoic, pyruvic, and dichloroacetic acids, it was demonstrated that DTP induced H+ into chlorophyll specifically. 5-Hydroxypyrazoles, which seem to be dissociable, converted chlorophyll into pheophytin in vitro. These compounds also induced chlorosis in sedge seedlings (Cyperus serotinus Rottb.), when the seedlings were grown in media containing these compounds. However, 5-hydroxypyrazoles, which seem to be undissociable, and analogs having no hydroxy group caused neither the chlorophyll conversion in vitro nor chlorosis in the seedlings. Chlorosis in barnyardgrass seedlings (Echinochloa crus-galli Beauv. var. oryzicola Ohwi) induced by DTP was reversed by cultivating the seedlings in media containing DTP plus NaOH, KOH, NH4OH, Ca(OH)2, sodium acetate, sodium pyruvate, sodium succinate, or sodium fumarate. Accumulation of the vinyl pheoporphyrin fraction in 4- day-old etiolated radish cotyledons (Raphanus sativus L. `Minowase 2') was enhanced by incubating the cotyledons with {delta}-aminolevulinic acid in the dark. However, simultaneous treatment with {delta}-aminolevulinic acid and DTP reduced accumulation of the fraction and promoted formation of the uro, copro, and protoporphyrin fractions. These results suggest that DTP blocks the synthesis of protochlorophyllide in intact plants and induces consequent chlorosis, and the H+ -donating activity of DTP might cause the reduction of protochlorophyllide biosynthesis.

2 Present address: Department of Agronomy, University of Illinois, Urbana, Illinois 61801.

1 Research from a doctoral thesis submitted by K. K. to the Faculty of Agriculture, The University of Tokyo, Japan.






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Copyright © 1979 by the American Society of Plant Biologists