The storage, compartmentalisation and transport of salt in plants that grow in areas of high salinity

In areas where irrigation is used up to 40% of arable land has high salinity. Unfortunately many crop plants are glycophytes and are therefore not tolerant to high salt levels. Much research has been carried out using the glycophyte Arabidopsis thaliana and salt tolerant (halophyte) plants with the aim of discovering the mechanisms of salt control in plants, and to identify genes that may be involved in salt tolerance.

It is hoped that a deeper understanding of mechanisms employed by salt tolerant plants to deal with ion toxicity will enable breeders to develop crops that can grow in areas of high salinity and have increased yields. Two of the mechanisms employed by halophyte plants to cope with high levels of salt are storage through compartmentalisation and restriction of long distance transport of salts from the root to the aerial parts of plants.

Salt storage - Compartmentalisation

One of the ways in which plants are able to control excess salts is to store them in their vacuoles. This results in a reduction of sodium levels found in the cytoplasm Compartmentalisation of salt in this way has two major positive impacts:

1. Sodium is separated from cytosolic enzymes - excess sodium leads to an inhibition in enzyme function
2. compartmentalisation of sodium in the vacuoles helps to maintain the osmotic potential.

The ability to compartmentalise salt into the vacuoles is one of the major determinants of the levels of salt that are plant is able to tolerate, and hence has a large impact upon the soil that a plant is able to grow in. The way in which salt is up took into vacuoles is well known and involves tonoplast pyrophosphatase and ATPases.

Control of long distance salt transport

A further way in which plants are able to control the impact of salt and ion toxicity is through long distance transport mechanisms. By restricting the uptake of salt from the root to the aerial parts of the plant the impact of salt on developing tissue, and areas of respiration can be reduced. Another way in which a plant is able to deal with increased salt levels is to store salt in older leaves; this helps to keep the concentration of salt low in new still developing leaves.