Evaluating the allelochemical effects of Syzygium cumini leaves extract on Microcystis aeruginosa by pulse-amplitude-modulated fluorometry and flow cytometry

The allelochemical effects of Syzygium cumini leaves extract (SCLE) on the growth inhibition and physiological properties for Microcystis aeruginosa were evaluated in laboratory setting. The chlorophyll-a (Chl-a) concentration of the algae was 24.4 mu g L-1 and the relative content of Chl-a was 0.9% at 2.0 g L-1 dose of SCLE treatment till the end of 15 d experiment. Results from fluorescein diacetate and propidium iodide showed SCLE inhibited esterase activity at early time, and affect cell integrity at later period. Inhibition of photosynthetic activity was reflected by relative electron transport rates (rETRs), the maximal electron transport rate (rETR(max)) and quantum yield of photosystem II (F-v/F-m) of algal cell. The photosynthetic parameters inhibited by SCLE occurred more rapidly than cell growth suggested the causative relationship though the effectiveness is temporary or at early stage.