Histone deacetylase activity and phytotoxic effects following exposure of duckweed (Lemna pausicostata L.) to apicidin and HC-toxin

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 historic deacetylase (HD) activity from duckweed plantlets; the effective concentration (EC50) for inhibition of HD was 5.6 and 1.1 muM for apicidin and HC-toxin, respectively. Approximately 65 and 85% of in vitro HD activity was inhibited by 50 muM apicidin or HC-toxin, respectively. Exposing duckweed for 72 h to apicidin or HC-toxin (25 or 50 muM) 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 muM apicidin resulted in chloroplast deterioration indicated by loss of orientation and excess starch accumulation. In roots, a 72-h treatment with 50 muM apicidin resulted in the loss of the root cap and increased vacuolization and starch accumulation in plastids.