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Efflux of K+, Mg2+, Ca2+ ions from algal cells as signals of cell membrane permeability, inductively coupled plasma mass spectrometry (ICP-MS) as detection method of ions, the present research investigated effects of allelochemical eathyl-2-methyl acetoacetate (EMA) isolated from Phragmites communis on cell membrane permeability of Microcystis aeruginosa, Chlorella pyrenoidosa and Chlorella vulagaris. The results showed that, when the cells were boiled for 10 min and the membrane was destroyed absolutely, the K+ efflux of M. aeruginosa and C. pyrenoidosa were 1.45 and 1.59 microg x (10(9) cell) (-1), respectively. When the concentration of EMA was 2 mg x L(-1), the K+ efflux of M. aeruginosa and C. pyrenoidosa were 1.38 and 1.40 microg x (10(9) cell)(-1), respectively. The K+ efflux of M. aeruginosa and C. pyrenoidosa reached 1.44 and 1.58 microg x (10(9) cell)(-1) while the EMA was 4 mg x L(-1). When the concentrations were 2 mg x L(-1) or 4 mg x L(-1) the K+ efflux reached more than 95% of the total ion amount in M. aeruginosa and C. pyrenoidosa cells. But when EMA concentration was 4 mg x L(-1), K+ efflux of C. vulagaris was 0.64 microg x (10(9) cell)(-1), which was only 31.5% of total K+ amount in C. vulagaris. Effects EMA on efflux of Mg2+ and Ca2+ were similar to those of K+. The results indicated that EMA destroyed the cell membrane of M. aeruginosa and C. pyrenoidosa but not C. vulagaris. This is one of the mechanisms of EMA species-selective antialgal.

Using allelochemicals produced by macrophytes to control harmful algae is a novel antialgal method. The present research investigated effects of the species-specific antialgal allelochemical EMA on activities of antioxidant enzymes of Chlorella pyrenoidosa and Chlorella vulagaris. The results showed that 0.25 mg/L of EMA increased activities of superoxide dismutase (SOD), peroxidase (POD)and catalase (CAT) of C. pyrenoidosa and C. vulagaris. With the increase of EMA concentrations, activities of the 3 enzymes of C. pyrenoidosa decreased sharply. The activity of SOD of C. pyrenoidosa decreased to 0 when the EMA were 4 mg/L. With the increase of EMA concentrations, activities of the 3 enzymes of C. vulagaris increased to as higher as 3-4 folders of that of the control set. The results gave hints to elucidate the species-specific antialgal mechanisms of EMA.