Physiological responses and chromosomal aberration in root tip cells of Allium sativum L. to cerium treatments

Lower concentrations of REEs promote plant growth, whereas higher concentrations of REEs negatively affect plant growth, soil accumulation, and environmental pollution. To clarify the mechanism of cerium (Ce) toxicity on Allium sativum, the effects of Ce(IV) on mitosis in root tip cells and physiological responses were studied. Roots growth, mitosis, chlorophyll and malondialdehyde contents, and activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase were measured after treatments with Ce(IV). Lower Ce concentrations (0.4 and 4 mu M) increased leaf chlorophyll content and enhanced SOD and catalase activities. Higher Ce concentrations (40 and 100 mu M) decreased chlorophyll content and inhibited root growth, but enhanced malondialdehyde contents and catalase and APX activity in roots and leaves. SOD activity was inhibited after 12 days of treatment with 100 mu M Ce. Treatment with > 100 mu M Ce caused chromosomal aberrations (e.g., sticky chromosomes, chromosomal fragments, and bridges) in root tip cells. Chromosomal aberrations in root cells induced by high Ce concentrations might be associated with inhibition of root growth. Changes in antioxidant enzyme activities suggested that Ce(IV) induced antioxidative stress responses and that Ce(IV) treatment first damaged root cells and subsequently affected physiological processes in leaves.