The inhibition of photosynthetic electron transport by methyl parathion.

The effect of methyl parathion (metacid-50), an organophosphorous insecticide, on the Hill reactions of isolated mesophyll chloroplasts of Sorghum vulgare was studied. The pesticide was found to inhibit the Hill reaction with all the Hill oxidants tested, namely potassium ferricyanide,2,6-dichlorophenol indophenol and para-benzoquinone. The concentration of the pesticide required to inhibit 50% of the control Hill activity (I50value) was found to vary with the different Hill oxidants.