Cytochemical and quantitative study of the structural changes induced by ethidium bromide in plant mitochondria

A study was made of the effect of 100 μg ml-1 ethidium bromide on the mitochondrial population of Allium cepa L. root meristematic cells. The structural modifications induced in mitochondria were quantified by planimetry done on electronmicrographies. Growth and mitochondrial division between the 6th and 12th hours seems to occur. The appearance of electron-opaque structures in the mitochondrial matrix was also planimetrically quantified, as well as the appearance of some electron-transparent areas. Cytochemistry and enzymatic digestions were carried out of the electron-opaque accumulations appearing in the matrix. They were highly contrasted by alcoholic PTA (preferential for basic proteins) but not by Feulgen-like stains or by EDTA method (preferential for RNP). The electron-opaque accumulations were neither digested by DNAase, or RNAase but they readily disappeared under pepsin or trypsin digestions. Given the direct inhibitory action of EB on mitochondrial transcription and translation, this basic protein(s) accumulated must be translated on a nuclear message and on cytoplasmic ribosomes