Isolation and characterization of antialgal allelochemicals from Arundo donax L.

We isolated and characterised the allelochemicals from Arundo donax L. (giant reed), these were very inhibitory to toxic and bloom-forming cyanobacterium Microcystis aeruginosa. The methanol extract of dry biomass of giant reed shoot quickly inhibited the algal growth. Through solvent extraction, the methanol extract was fractioned into neutral and acidic fractions, both these fractions also inhibited the growth of M. aeruginosa, but the neutral fraction was more inhibitoy than acidic fraction. The neutral fraction was analyzed by gas chromatography/mass spectrometry (GC/MS) and was found to contain several potential allelochemicals, including indoles, ketones, esters, alcohols, etc. Among them, 3-(dimethylaminomethyl)indole (i.e. gramine, an alkaloid) was found in the neutral fraction. Gramine inhibited the M. aeruginosa at 0.47 mg.L(-1) medium effective concentration (EC(50.3d)) and proved one of the strongest antialgal allelochemicals from aquatic plants.