Jung Sup Choi

Herbicidal Activity of Chrysophanic Acid in Semi-field Condition

ABSTRACT Herbicidal activity and characteristics of chrysophanic acid were investigated in semi-field condition. At early and middle post-emergence, Trifolium repens appeared to be very susceptible to chrysophanic acid of 2,000 μg mL -1 . However, herbicidal activity of chrysophanic acid of 2,000 μg mL -1 estimated by visual injury to Artemisia princeps was not caused considerable phytotoxicity. Also by foliar application, the concentration of crysophanic acid for effectively control to Polygonum aviculare was much higher than 2,000 μg mL -1 . Herbicidal activity of chrysophanic acid to Echinochloa crus-galli, Cypres difformis, Setaria viridis, Digitaria sangguinalis, Bidens tripartita by foliar application was more effective at concentration ranges from 4,000 to 6,000 μg mL -1 . These results suggest that chrysophanic acid demanded for higher than 2,000 μg mL -1 to successful weed control in the field condition.Key words: chrysophanic acid; impermeability; natural herbicide; semi-field condition; treatment dosage.

Isolation and characterization of a novel metagenomic enzyme capable of degrading bacterial phytotoxin toxoflavin

Toxoflavin, a 7-azapteridine phytotoxin produced by the bacterial pathogens such as Burkholderia glumae and Burkholderia gladioli, has been known as one of the key virulence factors in crop diseases. Because the toxoflavin had an antibacterial activity, a metagenomic E. coli clone capable of growing well in the presence of toxoflavin (30 μg/ml) was isolated and the first metagenome-derived toxoflavin-degrading enzyme, TxeA of 140 amino acid residues, was identified from the positive E. coli clone. The conserved amino acids for metal-binding and extradiol dioxygenase activity, Glu-12, His-8 and Glu-130, were revealed by the sequence analysis of TxeA. The optimum conditions for toxoflavin degradation were evaluated with the TxeA purified in E. coli. Toxoflavin was totally degraded at an initial toxoflavin concentration of 100 μg/ml and at pH 5.0 in the presence of Mn2+, dithiothreitol and oxygen. The final degradation products of toxoflavin and methyltoxoflavin were fully identified by MS and NMR as triazines. Therefore, we suggested that the new metagenomic enzyme, TxeA, provided the clue to applying the new metagenomic enzyme to resistance development of crop plants to toxoflavin-mediated disease as well as to biocatalysis for Baeyer-Villiger type oxidation.