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

Abstract

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 μg 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 [ 14C]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.