ABSTRACT
This work confirm the allelopathic toxic effect of both cell-free medium in log and death phase of growth of Microcystis aeruginosa on chromosomal changes of Allium cepa root tips and the plumule formation of Zea mays seedlings. The results showed high significant inhibition of mitotic index in Allium cepa root tips in addition, chromosomal abnormalities were also detected. There were morphological change occurred in the plumule formation of Zea mays seedlings. The results revealed that, seed soaked in log phase cell-free medium had less inhibitory effect on plumule formation than that the seed soaked in death phase cell-free medium of M. aeruginosa. This was confirmed by the allelopathic effect of toxins released during death phase of growth was more than log phase.