Studies on the Sites of Inhibition of Photosynthetic Electron Transport in Barley by DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane)

Abstract

The effect of DDT in resistant and susceptible barley on various photosynthetic electron transport activities involving photosystems 1 and 2 functioning alone and in series is reported. Whereas none of the measured activities in resistant barleys were affected by DDT treatment, in susceptible barley two sites of interaction of DDT with the photosynthetic electron transport chain were demonstrated. The first site of inhibition was located before photosystem 2, between the sites of electron donation from diphenylcarbazide at pH 6·0 and 8·0, and on the oxidizing side of the inhibitions resulting from tris washing or heat treatment. Mn²⁺ ions, which can act as donor before photesystem 2, appeared to donate electrons on the H₂O side of the site of inhibition by DDT. The second site of DDT inhibition was located in the path of electron flow from photosystem 2 to NADP⁺ or diquat, and was demonstrated by using dichlorophenolindophenol and phenylenediamines as electron donors.