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 I-50-value is 48 mu g mL(-1). Evidences from chlorophyll fluorescence show that tenuazonic acid interrupts electron transport between Q(A) and Q(B) 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 [C-14]atrazine, it is shown that tenuazonic acid does not share the same binding environment with atrazine despite their common action target: the Q(B)-site. It is concluded that tenuazonic acid is a member of a novel class of PSII inhibitors. (C) 2007 Elsevier B.V. All rights reserved.