ARS | Publication request: EFFECTS OF APICIDIN AND HC-TOXIN ON DUCKWEED (LEMNA PAUSICOSTATA L.)

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: August 23, 2001
Publication Date: N/A

Interpretive Summary: Apicidin and HC-toxin are toxins produced by fungi that have not been tested as herbicides. This study showed that both toxins are effective at low concentrations against duckweed, a small aquatic plant. It also confirms that the toxins work by inhibiting the enzyme histone deacetylase. This enzyme controls gene expression in plants. This unique site of action may provide a new avenue for development of new herbicides, which are needed because of herbicide resistance and toxicity problems.

Technical Abstract: The effects of two cyclic tetrapeptide fungal toxins, apicidin and HC-toxin, on duckweed (Lemna pausicostata L.) were examined. Both toxins inhibited histone deacetylase (HD) activity measured in crude extracts from duckweed plantlets. The effective concentration (EC50) values for the inhibition of HD were 5.6 and 1.1 uM for apicidin and HC-toxin, respectively. Approximately 65 and 85% of in vitro HD activity was inhibited by 50 uM apicidin or HC-toxin, respectively. Exposing duckweed for 72 h to apicidin or HC-toxin (25 or 50 uM) enhanced cellular leakage, impaired chlorophyll synthesis and inhibited growth (cell division). At equivalent concentrations, the effects of HC-toxin on these parameters were more pronounced than those of apicidin. In fronds, 72 hours of exposure to 50 uM apicidin resulted in chloroplast deterioration as evidenced by loss of characteristic orientation within cells and excess starch accumulation. In roots, a 72 h treatment with 50 uM apicidin resulted in the loss of the root cap, increased vacuolization and starch accumulation in plastids.