Transgenic tomato

By Our Science Correspondent

BANGALORE, JULY 31. Introducing a single gene, Canadian and U.S. researchers have been able to create a transgenic tomato which not only flourishes in highly saline environment but also produces edible fruit.

Some 60 million hectares of good agricultural land, accounting for one-fourth of all irrigated land in the world, has reportedly been affected by irrigation-induced salinity. In India, it is estimated that over three million hectares of irrigated land is currently affected by salinity.

Salinity plays havoc on most plants, upsetting their ability to take in water through their roots and causing dehydration. Excess sodium also disrupts key biochemical processes inside plant cells.

To utilise potentially fertile land, scientists have been trying to use new tools provided by molecular biology to see if plants could be genetically engineered to grow well in saline soils. According to one school of thought several genes would have to be successfully introduced into a plant in order to make it salt- tolerant.

But the work carried out by Dr. Hong-Xia Zhang of the University of Toronto and Dr. Eduardo Blumwald of the University of California, Davis, suggest that introduction of a single gene might suffice.

In 1999, Dr. Blumwald and his colleagues found that a weed, Arabidopsis thaliana, widely used as a model plant for laboratory research, could be made salt-tolerant by over-expressing its gene for AtNHX1 so that this protein was produced in excess. Now with the tomato, Dr. Blumwald and Dr. Zhang demonstrated that the over-expression of the same gene could confer salt-tolerance to an agricultural crop.

In an article in the coming issue of the journal, Nature Biotechnology, Dr. Zhang and Dr. Blumwald report that these transgenic tomatoes could flourish in highly saline water which killed off ordinary tomato plants.

The tomatoes were able to sequester the excess sodium ions in special compartments, called vacuoles, inside cells. They were thus able to avoid water loss through osmosis and also the toxic effects of excess sodium. Taken together, the results demonstrated the ability of transgenic plants to use salty water for growth.

High levels of sodium and chlorine could be found in the leaves of transgenic tomatoes grown in highly saline water. But there was only marginal increase of these chemicals in the fruit. Although the fruit was somewhat smaller, the number of fruits produced did not decline when the transgenic plants were grown in highly saline environment.

``The high concentration of salt in the leaves, and not in the fruit, demonstrates the potential use of these transgenic plants for agricultural use in saline soil,'' they observed in the paper.

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