Pentachlorophenol Inhibits Photosynthetic Electron Flow and Quenches Chlorophyll Fluorescence after Preillumination

The pesticide PCP was shown to inhibit the Hill reaction in broken chloroplasts (I50 = 15 jam) and to quench chlorophyll fluorescence. Both effects require preillumination. In contrast to the common “phenol-type” inhibitors, neither inhibition of Hill reaction nor chlorophyll fluorescence quench were affected by pretreatment of chloroplast with trypsin instead o f preillumination. An inhibition site differing from the “phenol type” inhibitors is therefore assumed. The results presented indicate that the observed light requirement is due to electron transport through PS II. Measurements of intrinsic tryptophane fluorescence phobic environment.