Action of tenuazonic acid, a natural phytotoxin, on photosystem II of spinach

Tenuazonic acid (TeA) is a putative phytotoxin obtained from Alternaria alternata, the organism that can cause brown leaf spot disease of Crofton weed (Eupatorium adenophorum). It is demonstrated here that the tenuazonic acid inhibits the activity of photosystem II (PSII); the I50-value is 48 μg mL−1. Evidences from chlorophyll fluorescence show that tenuazonic acid interrupts electron transport between QA and QB on the acceptor side of PSII. It does not have an effect on the antenna pigments, the oxygen-evolving complex (OEC) at the donor side of PSII. On the basis of the fluorescence induction kinetics and competition experiments with [14C]atrazine, it is shown that tenuazonic acid does not share the same binding environment with atrazine despite their common action target: the QB-site. It is concluded that tenuazonic acid is a member of a novel class of PSII inhibitors.