Salt Tolerance in plants

Salinity is known to affect at least 20% of all arable land and the amount of land affected is doubled in areas that require irrigation. This has a major affect upon the plants that can grow in these regions, and if salinity becomes to high it is often the case that fields need to be abandoned and no crops are able to grow.

Although plants require salts for development and growth, the vast majority of plants suffer from ionic and osmotic stresses when grown in areas of high salt, such as arid regions with poor drainage, coastal areas, and areas where irrigation has left a residual deposit of salts. Even though most plants suffer badly in areas of excessive salts, some have developed to become salt tolerant.

Classifications of plants with regards to salt

There are two main classes of plants with regards to salt; those that can grow in salty conditions and those that cannot.

1. Halophytes - These plants have evolved so as to tolerate high salt levels.
2. Glycophytes - These plants cannot tolerate high salt levels.

Unfortunately most crop species belong to the glycophyte class of plants. Some of the common symptoms associated with glycophyte plants when grown in areas of high salinity include:

1. Osmotic stress
2. Increased ionic stress
3. Oxidative stress
4. Nutritional disorders
5. Sodium toxicity
6. Chloride sensitivity

Even though halophytes are able to tolerate and grow in soil that has a high salinity their growth can still be affected by salt levels; this is usually as a result in a decreased osmotic potential in salty conditions which limits the ability of plants to uptake water.

Research into salt tolerance in plants

As mentioned above over 20% of the worlds arable land is affected by salt. It is thought that by breeding plants that are resistance to high saline levels may result in this land becoming available or more productive for crop species. With this in mind much research is being carried out into salt tolerance in plants. This research can be broke down into the four main areas:

1. Salt toxicity and tolerance physiology - the metabolic and cellular response to salt
2. Analysis of mutant plants that have altered responses to salt tolerance
3. Salt transport mechanisms - ion transporters involved in salt uptake, compartmentalisation, and control mechanisms
4. Genes involved in salt regulation