The Fungal
Phytotoxin Alternariol 9‑Methyl
Ether and Some of Its Synthetic Analogues Inhibit the Photosynthetic
Electron Transport Chain
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Abstract
Alternariol and monomethylalternariol
are natural phytotoxins produced
by some fungal strains, such as <i>Nimbya</i> and <i>Alternaria</i>. These substances confer virulence to phytopathogens,
yet no information is available concerning their mode of action. Here
we show that in the micromolar range alternariol 9-methyl ether is
able to inhibit the electron transport chain (IC<sub>50</sub> = 29.1
± 6.5 μM) in isolated spinach chloroplasts. Since its effectiveness
is limited by poor solubility in water, several alternariol analogues
were synthesized using different aromatic aldehydes. The synthesized
6<i>H</i>-benzo[<i>c</i>]cromen-6-ones, 5<i>H</i>-chromene[4,3-<i>b</i>]pyridin-5-one, and 5<i>H</i>-chromene[4,3-<i>c</i>]pyridin-5-one also showed
inhibitory properties, and three 6<i>H</i>-benzo[<i>c</i>]cromen-6-ones were more effective (IC<sub>50</sub> = 12.8–22.8
μM) than the lead compound. Their addition to the culture medium
of a cyanobacterial model strain was found to inhibit algal growth,
with a relative effectiveness that was consistent with their activity <i>in vitro</i>. In contrast, the growth of a nonphotosynthetic
plant cell culture was poorly affected. These compounds may represent
a novel lead for the development of new active principles targeting
photosynthesis