Genetically Engineered Plants Reduce Environmental Toxins

When we speak about genetically modified organisms (GMOs), we often think first about herbicide tolerant (Round-Up Ready) or insect resistant (BollGard) crops. But plants can be genetically engineered perform functions other than insect resistance and herbicide tolerance. My first post described one example: using plant genetic engineering to improve the quality of life for celiac disease patients. Bioremediation, the use of GMOs to reduce chemical contaminants in the environment, is another application of genetic engineering.

Bioremediation is the process of using live organisms to degrade toxic compounds. Phytoremediation is bioremediation using plants as the live organisms. In 2010 a research group at Nankai University published the results of their studies on phytoremediation of the herbicide, atrazine.

Atrazine is one of the most widely used herbicides in crops. Limiting weeds in the field reduces competition for water and nutrients. In corn production, for example, weed control using atrazine can lead to yield increases of 1–6%. However, atrazine is a relatively stable compound, degraded slowly in soil by microbes. It may be carcinogenic and has been associated with birth defects and endocrine disruptions. Atrazine accumulation in the soil might damage crops that are planted after atrazine treatment of fields. For these reasons, it is important to have a method to degrade atrazine in soil. One approach to increasing degradation of atrazine and other pesticides is phytoremediation.

Among the soil microbes that naturally degrade atrazine are Pseudomonas and Arthrobacter. These bacteria contain the atrazine chlorohydrolase gene (atzA), that converts atrazine to the non-toxic hydroxyatrazine. The Nankai University researchers genetically engineered (GE) plants to add the atzA gene. They tested the resulting GE plants for their ability to degrade atrazine in soil.

Non-GE plants grew as well as GE plants if the plants were grown in soil without atrazine. But in soil containing atrazine, non-GE plants were shorter and weighed less than plants genetically engineered to contain the atzA gene. Since atrazine acts by destroying chlorophyll in the leaves, the GE plants were tested for changes in chlorophyll content. When GE and non-GE plants were grown in soil containing atrazine, the chlorophyll in non-GE leaves decreased. The chlorophyll level of GE plants remained unchanged, indicating protection of the chlorophyll and therefore the plant by the introduced gene.

But will the GE plants remediate contaminated cropland? That is, can they remove atrazine from the soil, reducing damage to successive crops and reducing potential effects on human health? It’s still unclear how these plants will perform in the field. However, after growing GE plants in soil containing atrazine for 90 days, no atrazine remained in the soil. While preliminary, these data suggest that GE plants can be used for phytoremediation of an important herbicide in soil.

H Wang, X Chen, X Xing, X Hao, and D Chen. 2010. Transgenic tobacco plants expressing atzA exhibit resistance and strong ability to degrade atrazine. Plant Cell Reports 29: 1391 – 1399. DOI: 10.1007/s00299-010-0924-7