An example of pathogens in our crops causing human disease is illustrated in the incidence of the fungus Claviceps purpurea which causes a disease called ergot. Ergot was found in rye in the 1600’s. The rye was used to make bread. Ergot causes hallucinogenic reactions (it contains an LSD precursor) and caused people to behave in uncontrollable ways. This was interpreted as being possessed by demons or spirits and led to the death of many people throughout Europe and the USA whose strange behavior led to the accusation that they were witches.
Figure 36. Ergot in rye (click to enlarge)
More details can be found at:http://www.uh.edu/engines/epi1037.htmhttp://www.plant.uga.edu/labrat/ergot.htm
There are many other microorganisms that can attack our food supply and that we don’t know are there until people begin to get sick. It is important that scientists investigate how these tiny invaders enter into the food crop and are able to multiply, thus causing changes in the plant or producing toxic proteins that make us sick when we consume the plant.
How can we alter the plants so that they do not allow the microorganisms to enter the plant, grow and spread and ultimately make us sick?
NOTE: Activity 4 can be used at this time if it was not introduced during the discussion of "Historical Perspectives of Plant Diseases".
It is now possible to alter some foods so that their nutritional quality is improved thus impacting the health of people who consume it. One example is the possibility of obtaining rice varieties with a high level of vitamin A and a better iron uptake. This could help to alleviate the nutritional problems of large groups of people for whom rice is the primary food. Rice is the staple food for more than half of the world's population - over 3 billion people! This is discussed in detail in the following websites:http://www.goldenrice.org/http://cls.casa.colostate.edu/TransgenicCrops/hotrice.html
Mycotoxins in corn are potentially dangerous human and animal toxins produced by fungi that cause plant disease. Insect larvae can damage the plant and this allows fungal spores to enter. These fungi may produce mycotoxins which can be fatal to some animals and are possibly related to human cancers. Using genetically modified hybrids allows us to control the ability of insects and diseases to attack our crops while at the same time reducing our dependence on chemical sprays that are harmful to us and to the environment.
A gene (Bt) from the bacterium Bacillus thuringiensis can be inserted into a crop such as corn. When a pest such as the European corn borer begins feeding on this plant, it ingests the protein that is encoded by the Bt gene and translated in the corn plant. This protein forms crystals that penetrate the cells lining the insect's gut and the insect subsequently dies. Generally, uncontrolled pests may cause direct loss by eating leaf tissue, vascular tissue, and grain. Indirect damage may result from increasing the risk of stalk rots, ear rots, mycotoxins contamination of the grain, stalk breakage, and ear-drop.
See the following website for information on Bt corn:
Thus, new genes can be introduced into plants and animals that will produce healthier, more nutritious crops and meat without the use of excessive amounts of pesticides or growth hormones and antibiotics.
How do we determine if a new gene has been incorporated into our plant or animal?
How can we study the expression of these genes within the cell?
Go to Activity 6 (Polymerase chain reaction and microarray)