BARREN, salt-laden soils could be transformed into lush farmland thanks to
plants genetically modified to be salt tolerant.
The GM plants can grow on saline land because they store excess salt in their
leaves鈥攕o as well as making saline soil productive they could also be used
to remove the salt. 鈥淎 farmer can clean the soil and grow a crop and make a
profit at the same time,鈥� says Eduardo Blumwald of the University of California
at Davis, whose team has already created a salt-tolerant GM tomato and is making
progress with other crops.
鈥淏lumwald has made the key breakthrough that has been needed in salt
tolerance research for the last 30 years,鈥� says Edward Glenn of the University
of Arizona in Tucson, who studies salt-loving plants.
Advertisement
It鈥檚 thought that as much as a quarter of the world鈥檚 irrigated farmlands
have become saline. Irrigation water often contains tiny amounts of salt, which
builds up on the land over time as a result of evaporation.
Researchers have been trying for years to create salt-tolerant crops, with
little success. Some gave up on the task, believing that salt tolerance involved
so many genes that adding the trait to crop plants would be too complicated.
But by manipulating just one gene, Blumwald and Hong-Xia Zhang of the
University of Toronto have created a salt-tolerant tomato plant that stashes
excess sodium ions in cellular sacks known as vacuoles. The gene they added
codes for a membrane transport protein called AtNHX1, which pumps sodium ions
into the vacuoles. The researchers ramped up the expression of the transporter
gene by adding a 鈥減romoter鈥� sequence which they took from the cauliflower mosaic
virus.
Blumwald discovered the transporter in 1985, while he was studying vacuoles.
It has since been found that numerous plants have similar
transporters鈥攊ncluding the tomato 鈥攁nd that they鈥檙e especially
abundant in naturally salt-loving plants.
However, it was only after the start of the project to sequence the genome of
the thale cress Arabidopsis thaliana, the plant most commonly used in
experiments, that Blumwald was able to identify and isolate the AtNHX1 gene. In
1999, Blumwald created a salt-tolerant Arabidopsis plant by increasing
expression of the gene (Science, vol 285, p 1256), but the tomato is
the first edible plant to be made salt-tolerant in this way.
He and Zhang say the GM plants can grow in salt levels of 0.2 moles per
litre鈥�50 times higher than normal plants can tolerate, and nearly half as
salty as seawater.
Although the transporter protein is found throughout the tomato plant, the
sodium accumulates only in the leaves. The fruits taste just like ordinary
tomatoes, the scientists say.