The uptake of cadmium by Allium cepa var. agrogarum L. and its effects on chromosome and nucleolar behavior in root tip cells

Abstract

<i>Allium cepa</i> var. <i>agrogarum</i> L. seedlings are sensitive to Cd stress. We used fluorescence imaging to indicate that Cd2+ was localized in cytoplasm in the epidermis of the basal parts of root and vascular tissues after Cd treatment. The nucleoli and the cell walls were the first storage sites of Cd²⁺. When Cd exposure was prolonged, severe irregularly-shaped nuclei were induced. We used silver nitrate staining to analyze the effects of different concentrations (1–300 μM) of cadmium chloride on chromosome, nucleolus and nucleolus organizer regions (NORs) in root tip cells. Cd²⁺ induced c-mitosis, chromosome bridges, chromosome stickiness and micronuclei. More than 100 μM Cd²⁺ could induce nucleolar material extruded from the nucleus into the cytoplasm. The abnormal phenomena of the nucleolar cycle during mitosis induced by Cd stress contained the nucleoli, which did not exist normally and melted gradually. More silver-stained particles were seen on chromosomes at the metaphase; more silver-stained particulates were localized on the sticky chromosomes, chromosome bridges and cytoplasm. Nucleolar reconstruction was inhibited at the telophase, NORs were localized on chromosomes of c-mitosis. The LysoTracker red stained results indicated that autophagy was active. The number of autolysosomes in roots of Cd-treated plants was more than that on control plant.