Easy on the eye

By Mark Finlayson, Checkbiotech

Most of us were told as children that eating carrots is good for your eye-sight. But imagine if our mothers had urged us to have another helping of french fries for the same reason. Now, transgenic potatoes equipped with a bacterial gene of the biosynthetic pathway of carotenoids not only come in a very stylish orange hue, but offer a wide range of health benefits as well.

Carotenoids are pigments found in large amounts in carrots, apricots and other intensely coloured vegetables and fruits. Some members of this large family of molecules (such as β-carotene) are processed to Vitamin A, which in turn is used to maintain healthy cells in the eye, and is further required in the retina to produce nerve signals from incoming light. Vitamin A is also essential for a normal development of the embryo during pregnancy, as well as many other functions.

Other carotenoids include lutein, which has proved helpful in preventing macular degeneration, a leading cause of blindness. Lycopene, a molecule with a protective effect against prostate and intestinal cancers and heart attacks, is yet another beneficial carotenoid. Although the exact mechanisms of action are still unclear, it is becoming more and more evident that carotenoids have more to offer than meets the eye.

Unfortunately though, white-fleshed potatoes, such as Solanum tuberosum, have a very low carotenoid content. So, being the world’s fourth largest source of calories, and quite often the main dietary staple for low-income consumers, a nutritional enhancement of these widely spread root crops makes a lot of sense.

In the last few years, successful attempts have been made to increase the carotenoid levels by regulating certain metabolic steps or by cross-breeding. Only slowly are scientists beginning to understand the complex factors that regulate the biosynthesis of carotenoids.

A team of researchers, lead by Mark Taylor of the Scottish Crop Research Institute in Dundee has now produced potato plants expressing the bacterial crtB gene. This gene encodes phytoene synthase (phytoene is a precursor of carotenoids), an enzyme which has previously been shown to have a substantial effect on carotenoid content in carrots and tomatoes.

As a result, carotenoid content of potato tubers increased up to 6-fold, with three major carotenoids accounting for most of the accumulation: β-carotene, lutein and violaxanthin.

Although the extent of this increase will not provide 100% of the recommended daily intake of vitamin A, it can make a significant difference. Furthermore, the high lutein levels are also potentially beneficial, as previous experiments with dietary supplements have shown.

As the understanding of how our body uses and produces carotenoids grows, further possibilities will arise to design different carotenoid compositions for specific nutritional benefits.

With vitamin A already been transferred to rice varieties, Mark Taylor can also imagine other root crops being modified to contain higher levels of carotenoids.

“I don't see why cassava should not be engineered to produce vitamin A. In fact, as cassava is consumed in areas of the world suffering from vitamin A deficiency, it would make sense to do this. The technology is available.”

“Furthermore, other dietary supplements could be transferred to these crops. Folate, iron, vitamin C and tocopherols spring to mind immediately, as there are other plants where some of these have been successfully engineered.”

When asked about how long until his enhanced potatoes might be sold in stores, Dr. Taylor noted, “In Europe, there has been a luke warm reception to the concept of high carotenoid tubers - especially developed via a GM route.”

With European appetites dragging, Dr. Taylor may have to turn to other markets such as the US and Canada for his biofortified potatoes.

Yet, Dr. Taylor did note that the potato industry on a whole has developed an interest in potatoes that have an enhanced flavour and texture.

When asked if his vitamin A enriched potatoes tasted different compared to parent potato, Dr. Taylor acknowledged that they had not yet undergone such testing, however, “We shall test this at some stage.”

When Dr. Taylor’s potatoes eventually are ready to hit the fields, a potato a day might, one day, keep the doctor at bay.

Copyright by Checkbiotech