Electron microscopic investigation of benzidine e ect on maize root tip cells ultrastructure, DNA synthesis and calcium homeostasis

The e ect of various benzidine concentrations on the ultrastructural organization of maize root tip cells was investigated. Data showed that benzidine at concentration of 2:2 10−7{2:2 10−6 M did not cause noticeable changes of the ultrastructure. When benzidine concentration was increased up to 2:2 10−3 M several pathological changes occurred ending in the complete destruction of the cell. Radioautographic investigation to follow the penetration and facts of [1{1214C]benzidine into cells showed that the radioactive label reached the nucleus chromatine within 10 min. Then the label was detected in the nucleolus and the cytoplasmic organelles followed by excretion into vacuoles (60 min). Benzidine at 2:2 10−4, inhibited DNA synthesis in the nuclei. Cytochemical investigation showed that exposure to 2:2 10−4 M of benzidine for 24 h caused an inhibition of Ca2+{ATPase and an increase of the concentration of free calcium in the cytoplasm resulting from the release of calcium from the membrane system. Data suggest that ultrastructural changes are caused by disturbance of cell calcium homeostasis, resulting in a deregulation of the Ca2+ dependent metabolic processes