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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

New Plant Protection Mechanisms Under Development

Crop and Soil Environmental News, September 1997

Charles Hagedorn
Extension Specialist

Aluminum Tolerance Engineered into Crops

More than one-third of the arable land in the world suffers from soil acidity and aluminum toxicity, and low agricultural productivity in acid soils is directly attributable to the effects of aluminum. The problem is most severe in the humid tropics where crops such as corn, field bean, soybean and cotton do not grow well because of their high sensitivity to soil acidity. A research team in Mexico may have made a breakthrough to the aluminum problem in agriculture. By introducing a bacterial citrate synthase (Csb) gene into tobacco and papaya, the Mexican scientists have genetically engineered plants that are more tolerant to the aluminum. The research strategy relies on the fact that some plants tolerate aluminum by releasing citric that binds to the metal, making it difficult to enter plant roots. Transgenic plants expressing the Csb gene (taken from a soil bacterium) produced up to ten-fold more citrate in their roots and released four-fold more of the compound than control plants. When grown under extremely high aluminum and acidic conditions, transgenic Csb plants showed substantially lower root growth inhibition compared to the untransformed plants.

Biodegradable Plastic From Canola

British researchers are collaborating with scientists at Monsanto Corporation to develop a biodegradable material from canola (rapeseed) that could be used as a substitute for plastic. The cooperative project involves the insertion of three genes that make the plastic substitute into canola (the genes are from a bacterium found in soil). An output of 14 percent oil has been produced so far, but it is estimated that a 20 percent output will be required to make the process economically feasible. This oil is the material that can be used as a substitute in making plastic.

Transgenic Viral Insecticide

Researchers at the Boyce Thompson Institute for Plant Research at Cornell University have developed a protein that allows a virus to evade the immune systems of insect pests. The genetically engineered protein "enhancin" works by breaking down the tough interior lining of a bugís intestine, allowing the virus to infect and kill the insect. The "enhancin" enzyme apparently poses no threat to humans or other mammals because the acidity in the stomach degrades the "enhancin" protein and renders it harmless. For use as a bioinsecticide, the "enhancin" protein and a specific virus will be combined in crystals and injected into a leaf or other substance the insect pest eats. This method has proven effective against seven pests so far, including cotton bollworms, armyworms and the velvetbean caterpillar. Studies are also underway to attempt to genetically engineer "enhancin" directly in crop plants.

Algae Research May Provide Frost/Drought Resistance for Crops

Researchers at the University of Florida are trying to use compounds found in algae to develop agricultural crops that resist freeze, drought and salt-water damage. The research findings indicate that for the first time scientists have identified the precise mechanism by which algae make DMSP (dimethylsufoniopropionate), that is converted by algae enzymes into DMS (dimethylsulfide), a sulfur gas that helps clouds form in the atmosphere. The research furthers scientific understanding of the biological origin of atmospheric dimethylsulfide, which is a significant factor in the global sulfur cycle and may play an important role in climate regulation. The researchers have established the biochemistry of how algae convert the common compound methionine-which is found in all algae--into DMSP. Algae produce DMSP to protect themselves from the negative effects of high salinity and freezing. DMSP is also formed in some higher plants that are tolerant to drought, frost and salt stress. While this research is in an early stage, it may be possible to use genetic engineering to transfer the capacity to make the compound DMSP from simple marine organisms (algae) into agricultural crops. If crops could make DMSP, this could provide a useful degree of drought, frost and salt tolerance.

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