|
USA – GM CALCIUM-RICH SPUD UNDER RESEARCH
Calcium-enhanced potatoes offer a new healthy choice
30 September, 2005 - Checkbiotech
The majority of people do not consume enough calcium and are thus suffering from health problems. Transgenic potato tubers containing up to three-fold more calcium may soon be an edible tool for boosting calcium consumption.
The body needs calcium to reduce osteoporosis, a disease characterised by reduced bone density and the primary cause of bone fragility. The recommended amount of daily calcium intake depends on the person’s age. For example, nursing children need between 20 to 400 milligram of calcium per day. The older a child becomes, the more calcium it needs. A teenager should consumer around 1.2 gram calcium per day, whereas adults should eat 1.5 gram of calcium per day.
Dairy products are a good source of calcium. Cheese is especially rich in calcium. A 100 gram piece of Parmesan contains 1,180 milligram of calcium. Thus, the daily calcium need would already be met by eating a piece of cheese and drinking a glass of milk.
However, some individuals suffer from lactose intolerance and thus limit their
consumption of dairy products or even avoid it totally, while some ethnic groups do not use dairy products in their diet, or restrict them considerably. These individuals have to meet their daily calcium needs by eating vegetables and fruit.
Unfortunately, widely consumed vegetables, such as potatoes, grains and rice, do not contain enough calcium. For example, an average tuber of boiled potato contains only 20 milligram of calcium. Given that an average person would eat one boiled potato per day, one would consume 7.3 gram calcium in a year – the amount recommended for only one week!
“If we double or triple the amount of calcium in a tuber, we could provide several weeks worth of the dietary reference intakes of calcium,” said Dr. Kendal Hirschi from the Baylor College of Medicine in Houston, Texas, in his publication in the Journal of Agricultural and Food Chemistry.
The reason for Dr. Hirschi’s excitement was that his publication dealt with
transferring a gene that encodes the calcium transporter CAX1 to a potato variety.
CAX1 is a calcium transporter in the vacuole membrane of plants. The researcher’s hypothesis was that increased activity of CAX1 in potatoes should result in an increase in total calcium level. This hypothesis was based on his past research that CAX1 increased calcium levels in tobacco (Plant Cell, 1999).
Analyzing their data, the researchers found out that the transgenic potato tubers contained 1.5- to 3-fold more calcium than natural tubers, and in transgenic leaves, the calcium levels increased up to 1.7-fold. Since even the third generation of potato plants showed an increase in calcium content, the researchers believe that this trait is stable through successive generations.
Overall, comparing the mineral content and consistency of common potato varieties and calcium-enhanced potatoes, Dr. Hirschi’s group was not able to find any differences.
The researchers underline, however, that no single food source will rectify calcium intake deficiencies alone and the genetically enhanced potatoes follows suite. Thus, transgenic potatoes will not cure osteoporosis, but they rather will provide additional calcium and will be a model for the modification of the calcium content in many more food crops, Dr. Hirschi and his colleagues argue.
To assess the so called bioavailability of calcium (the amount of calcium that can be digested, absorbed and used by the body) further studies are needed. Right now, the researchers are undertaking feeding studies in mice to see if the transgenic potatoes are actually more nutritious. In addition, some experiments should assess if calcium-enhanced potatoes still taste like common commercial varieties.
Since there is some evidence that genetic transformation does not alter either the ethylene levels or the sugar content of tomatoes, Dr. Hirschi suggests that
transgenic potatoes will also taste like common varieties.
The research group has carried out some experiments to determine, whether a higher calcium amount in the tuber affects the vitamin C content of the potatoes. With greenhouse grown potatoes, they did not see any difference. In addition, the consistency appears to be similar, but at this point the researchers have not finished their work in this area. Dr. Hirschi told Checkbiotech.
Future studies will also be done to find out if increasing calcium levels will decrease the incidence of pathogen infection and post harvest decay, two major problems worldwide. “Our hope is that the modifications will lower the incidence of postharvest infection and will not alter the insect attacks on the plants,” Dr. Hirschi explained.
Plants need calcium for normal growth and development, and it is especially critical for correct cell wall and cell membrane formation. It is known that potatoes grown in calcium enriched soils have an increased tuber quality, whereas calcium deficiencies in potatoes result in internal disorders such as: hollow-heart, internal brown spot, brown center and reduced storage life. Thus, transgenic potatoes containing higher calcium levels could lead to better yields for farmers and a more nutritious product for consumers.
Dr. Hirsci looks forward to working with the Vegetable and Fruit Improvement Center
at Texas A&M. This center specializes in working with growers to bring new produce
options to consumers.
Dr. Hirschi and his team have recently carried out similar studies with tomatoes and carrots, and he noted, “We should try as many plants as possible.” The results of his study are encouraging, Dr. Hirschi said. However, a lot more work needs to be done to show these plants are durable and safe. “Working with plants is fun, because you can try to help people – but it is a slow process.”
Katharina Schoebi is a biologist and Chief Science Writer for Checkbiotech. Contact her at katharina.schoebi@bluewin.ch.
Kendal D. Hirschi et al. Genetic Manipulation for Enhancing Calcium Content in Potato Tuber. Journal of Agricultural and Food Chemistry. (2005) 53, pp. 5598-5603
Link to the abstract:
www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=15998121&dopt=Citation
Kendal D. Hirschi et al. Expression of Arabidopsis CAX1 in Tobacco: Altered Calcium Homeostasis and Increased Stress Sensitivity. Plant Cell. (1999) 11, pp. 2113-2122
|
