In 1924, Science magazine reported on a fatal case of potato
poisoning: James B. Matheney of Vandalia, Illinois, had gathered about
one and a half bushels of tubers, which had turned green due to sunlight
exposure.
Two days after eating the potatoes, most of his family –
wife, two daughters and four sons – showed symptoms of poisoning; the
only exceptions were James himself, who didn’t eat the potatoes, and a
breast-fed baby boy.
His wife, aged 45, died a week later, followed by
their 16-year-old daughter. The other five members of the family
recovered.
Although such fatalities are rare among human beings, farm animals often get sick or die after eating green potatoes. Symptoms include damage to the digestive system as well as loss of sensation, hallucinations and other neurological disturbances.
Death can be caused
by a disruption of the heart beat. The culprits are the toxic substances
solanine and chaconine; their concentration rises sharply with exposure
to light or during sprouting, and they protect the tubers from insects
and disease.
Solanine and chaconine belong to the large family of glycoalkaloids, which includes thousands of toxins found in small amounts in other edible plants, including tomatoes and eggplant.
These substances have
been known for over 200 years, but only recently has Prof. Asaph Aharoni of
the Plant Sciences Department begun to unravel how they are produced in
plants. He and his team have mapped out the biochemical pathway
responsible for manufacturing glycoalkaloids from cholesterol.
Their
findings will facilitate the breeding of toxin-free crops and the
development of new crop varieties from wild strains that contain such
large amounts of glycoalkaloids, they are currently considered inedible.
On the other hand, causing plants to produce glycoalkaloids if they
don’t do so naturally or increasing their glycoalkaloid content can help
protect them against disease.
Two years ago, in research reported in The Plant Cell, the scientists identified the first gene in the chain of reactions that leads to the production of glycoalkaloids.
In a new study published recently in Science,
they have now managed to identify nine other genes in the chain by
using the original gene as a marker and comparing gene expression
patterns in different parts of tomatoes and potatoes.
Disrupting the
activity of one of these genes, they found, prevented the accumulation
of glycoalkaloids in potato tubers and tomatoes.
The team then revealed
the function of each of the genes and outlined the entire pathway,
consisting of ten stages, in which cholesterol molecules turn into
glycoalkaloids.
An analysis of the findings produced an intriguing insight: Most of the genes involved are grouped on chromosome 7 of the potato and tomato genome. Such grouping apparently prevents the plants from passing on to their offspring an incomplete glycoalkaloid pathway, which can result in the manufacture of chemicals harmful to the plants.
The research was conducted by postdoctoral fellow Dr. Maxim Itkin, who worked with Dr. Uwe Heinig, Dr. Oren Tzfadia, Pablo D. Cardenas, Dr. Samuel Bocobza, Dr. Sergey Malitsky and Dr. Ilana Rogachev of Prof. Aharoni’s lab; as well as Dr. Tamar Unger of the Israel Structural Proteomics Center at the Weizmann Institute, and scientists from the National Chemical Laboratory in Pune, India, the Hebrew University of Jerusalem and the Wageningen University, the Netherlands.
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