Tolerance to Abiotic Stresses

The full potential yield of crops is rarely met because of environmental stresses. These include drought, cold and salt stresses and mineral toxicities. In most cases, advances to generate stress-tolerant plants by traditional breeding have been slow. This is partly because tolerance to
these stresses usually involves many genes and physiological processes.
For cold and drought tolerance, recent research has shown that a series of functionally different cold (COR) and drought response genes show common promoter regulatory sequences (CRT/DRE). Transcription factors which bind to these regulatory sequences have been identified which switch on the stress response genes in concert. Overexpression of the transcription factor (CBFI or DREB) in Arabidopsis by two separate groups conferred tolerance to freezing. In one case, the plants also withstood high salt stress.These results are significant because they show that introduction of a single regulatory gene can confer tolerance to stresses.
It may be that freezing injury in plants is mainly caused by dehydration as ice crystals form, so that drought and freezing tolerance may share common protective mechanisms.
Other approaches to stress tolerance include expression of compatible solutes (e.g. trehalose or glycine betaine or the amino acid proline) or antifreeze proteins, which order the water in cell cytoplasm and so reduce the freezing point or size of ice crystals which may form. They may also help in maintaining membrane integrity.
The application of microarray technology has major applications in helping to identify genes that are up-regulated when plants encounter environmental stresses, including genes involved in stress perception, signalling and tolerance. For example, this approach is being used to identify genes involved in response to salt tolerance.