Breeding Aims Stress Resistant Crops

Tomatoes have been genetically engineered enabling them to grow in salty water. These tomatoes take up salts from the soil and store it primarily in leaves.

Researchers have been able to identify several plant genes that are involved with stress tolerance. Some of these genes code for antioxidants, enzymes that modify lipids in the cell membrane, stress-response transcription factors, proteins that maintain ion homeostasis, heat shock proteins, or enzymes that synthesis important stress-response compounds. Some of these factors have been used to produce transgenic plants with increased stress tolerance.

Drought tolerance

Water is crucial for all living things. Plants use water as a solvent, a transport medium, an evaporative coolant, physical support, and as a major ingredient for photosynthesis. Without sufficient water, agriculture is impossible. Therefore, drought tolerance is an extremely important agricultural trait.

One way of engineering drought tolerance is by taking genes from plants that are naturally drought tolerant and introducing them to crops. The ressurection plant (Xerophyta viscosa), a native of dry regions of southernmost Africa, possesses a gene for a unique protein in its cell membrane. Experiments have shown that plants given this gene are less prone to stress from drought and excess salinity.

Some genes have been found that control the production of the thin, protective cuticle found on leaves. If crops can be grown with a thickened waxy cuticle, they could be better equipped for dealing with dryness.

Salt tolerance

Irrigation has enabled the transformation of arid regions into some of the world's most productive agricultural areas. Excess salinity, however, is becoming a major problem for agriculture in dry parts of the world. In several cases, scientists have used biotechnology to develop plants with enhanced tolerance to salty conditions.

Researchers have noticed that plants with high tolerance to salt stress possess naturally high levels of a substance called glycinebetaine. Further, plants with intermediate levels of salinity tolerance have intermediate levels, and plants with poor tolerance to salinity have little or none at all. Genetically modified tomatoes with enhanced glycinebetaine production have increased tolerance to salty conditions.

Another approach to engineering salt tolerance uses a protein that takes excess sodium and diverts it into a cellular compartment where it does not harm the cell. In the lab, this strategy was used to create test plants that were able to flower and produce seeds under extreme salt levels. Commercially available crops with such a modification are still several years away.