Interactive patterns of methyl mercury toxicity in nuclear and cell division of apical meristems of Elodea densa at low concentrations and long-term exposures in vivo

Abstract

Elodea densa plants continuously exposed to low levels of methylmercury (7.5 × 10−10 to 7.5 × 10−8 M) in a flowing water system over a 25-day period concentrated methylmercury in young tissues. Toxicity effects in apical meristems were not linear with dose and time but were interactive in response. Microscopic studies of plants treated at 7.5 × 10−10 M showed a predominance of "spaghetti" prophases, a gradual inhibition of mitosis, and imbalance of mitotic stages. Higher concentrations of methylmercury produced different effects: bi- and multi-nucleate cells, polyploidy, aneuploidy, and altered or incomplete cell walls. At the highest concentrations (7.5 × 10−8 M) total pycnosis developed in the apex within 11 days, followed by a disintegration of nuclear and cell contents. Demethylation in tissues was directly related to methylmercury concentrations in the tissues and to tissue age.