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

The effect of various benzidine concentrations on the ultrastructural organ ization of maize root tip cells was investigated. Data showed that benzidin e at concentration of 2.2 x 10(-7)-2.2 x 10(-6) M did not cause noticeable changes of the ultrastructure. When benzidine concentration was increased u p to 2.2 x 10(-3) M several pathological changes occurred ending in the com plete destruction of the cell. Radioautographic investigation to follow the penetration and facts of [1-12(14)C]benzidine into cells showed that the r adioactive label reached the nucleus chromatine within 10 min. Then the lab el was detected in the nucleolus and the cytoplasmic organelles followed by excretion into vacuoles (60 min). Benzidine at 2.2 x 10, inhibited DNA syn thesis in the nuclei. Cytochemical investigation showed that exposure to 2. 2 x 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 ul trastructural changes are caused by disturbance of cell calcium homeostasis , resulting in a deregulation of the Ca2+ dependent metabolic processes. (C ) 2000 Elsevier Science Ltd. All rights reserved.