Accumulation and Inhibitory Effects of Microcystin on the Growth of Rice and Broccoli

Microcystins (MCs) produced by cyanobacteria are severe hepatotoxins for mammalian and protein phosphatase inhibitors. Irrigation water for grain and vegetables is often contaminated with cyanobacteria and microcystin during warm seasons. We assessed the effects of various concentrations (0, 0.01 to $10{\mu}gmL^{-1}$) of microcystin-LR (MC-LR) and microcystin-RR (MC-RR) exposure on Oryza sativa (rice) and Brassica oleraces var. italica (broccoli). The $EC_{50}$ of leaves and roots of rice was 0.9 and $1.1{\mu}gMC-LRmL^{-1}$, respectively. The no observed effect level (NOEL) of rice was less than $0.1{\mu}gmL^{-1}$ ($100{\mu}gL^{-1}$). The $EC_{50}$ of the stems and roots of broccoli was 8.7 and $7.2{\mu}gMC-RRmL^{-1}$, respectively. There was no difference in the germination rate of broccoli among microcystin-RR concentrations. After exposure to 0, 0.01 to $10{\mu}gmL^{-1}$ MC-RR for seven days, 14, 89 and 154 ng mg-1 (dry weight) MC-RR accumulated in B. oleracea. These $EC_{50}$ values showed that microcystin-LR and -RR affected the growth of rice and broccoli. These findings suggest that MC is carried into terrestrial ecosystems via irrigation, and that the biota of higher ecological niches can be influenced by MC through bioaccumulation. Therefore, a guideline for MC concentrations in irrigation water should be set using the NOEL.