The Role of Plants in Environmental Toxicology

Michael J. Plewa

Interaction between Salmonella typhimurium and tobacco cells. The plant cell is the large kidney-shaped object; the bacteria, the darkly staining small rods. It is the bacteria that are studied for DNA damage after a promutagen has been activated by the plant cells.

Most of us are concerned about the poisoning of our planet. But even well- informed people may be unaware that plants accumulate, metabolize, and distribute environmental contaminants.

Plants can become a reservoir for these contaminants. Because plants are exposed to environmental pollutants, agricultural chemicals, and naturally occurring toxic agents, plant-activated agents may be introduced into the human food chain. Thus, effects of environmental toxins on plants have a global impact.

Our research uses cultured plant cells to identify promutagens and the biochemical pathways involved in their metabolism. Although promutagens do not damage DNA (the genetic material), they can be biologically transformed into mutagens, agents that produce mutant forms of plants or animals.

Plant and mammalian metabolic systems activate many promutagens. But several environmentally important agents - several s-triazine and thiocarbamate herbicides and plant-growth regulators such as maleic hydrazide - are preferentially activated by plant cells.

The plant cells (cultured tobacco, cotton, carrot, or maize Tradescantia) and microbes (bacteria or yeast cells) are incubated together. The plant cells are the activation system and the microbes are the genetic indicator organisms. After the microbes are spread on a selective medium, only mutant cells grow into individual colonies.

Researchers independently study the plant cells and microbes to determine their viability and evaluate each test agent's toxicity. Basic research uses this assay to explain the biochemical mechanisms of plant activation and to analyze plant-mediated antimutagens. Such research could potentially identify chemicals that reduce the toxicity of environmental contaminants.

Michael J. Plewa, professor of genetics, Institute for Environmental Studies, departments of Agronomy and Microbiology

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