The effects of two cyclic tetrapeptide fungal toxins, apicidin (from Fusarium spp.) and HC-toxin (from Cochliobolus carbonum), on duckweed (Lemna pausicostata L.) were examined. Both toxins inhibited histone deacetylase (HD) activity from duckweed plantlets; the effective concentration (EC50) for inhibition of HD was 5.6 and 1.1 μM for apicidin and HC-toxin, respectively. Approximately 65 and 85% of in vitro HD activity was inhibited by 50 μM apicidin or HC-toxin, respectively. Exposing duckweed for 72 h to apicidin or HC-toxin (25 or 50 μM) enhanced cellular leakage, impaired chlorophyll synthesis, and inhibited growth (cell division). At equivalent concentrations, the effects of HC-toxin were more pronounced than those of apicidin. In fronds, 72 h of exposure to 50 μM apicidin resulted in chloroplast deterioration indicated by loss of orientation and excess starch accumulation. In roots, a 72-h treatment with 50 μM apicidin resulted in the loss of the root cap and increased vacuolization and starch accumulation in plastids.
Histone Deacetylase Activity and Phytotoxic Effects Following Exposure of Duckweed (Lemna pausicostata L.) to Apicidin and HC-Toxin