Plants and salt ion toxicity

As much as 20% of all arable land is affected by high salt levels; this has a major impact upon the yield and type of plants that can be grown in these areas. Much research has been carried out into salt tolerance in plants with the hope that one day crop plants can be bred that have a higher tolerance to saline toxicity and will be able to grow or/and produce larger yields.

Much of the salt uptake into plants acts through passive networks such as those associated with cation transportation such as potassium ion channels. This section takes a look into the mechanisms that plants have developed to deal with ion toxicity.

Methods used by plants to deal with ion toxicity

There are many mechanisms that plants are able to employ in combating salt stress, retain homoeostasis and overcome ion toxicity. Some of these mechanisms include:

1. Restriction the mechanisms involved in salt uptake
2. control of long distance transport of salt
3. compartmentalisation of salt
4. extrusion of salt from the plant
5. Prioritising the maintenance of potassium to sodium ratio levels in the cytosol

Effects and control of ion toxicity in plants

The presence of increased salt ions can lead to many toxic affects. An excess of sodium at the root surface can seriously impact the uptake of other cations such as potassium; this can lead to disruption of membrane potential, cell turgor and the disruption of enzyme function. Plants are able to overcome this to a degree by operating selective high affinity potassium channels, however even with these mechanisms in place the presence of large quantities of salt in the soil means that the plant can not take up potassium at will, resulting in slower growth and a lack of vigour.

The presence of sodium ions in the cytoplasm can have a dramatic inhibitory effect to many enzymes. Interestingly even in salt tolerant halophytes increases in salt in the cytoplasm is toxic and the ratio of potassium to sodium ions in the cytoplasm is maintained similar to that seen glycophyte plants. To help to reduce the level of sodium in the cytoplasm halophyte plants compartmentalise excess salt in their vacuoles.

Calcium and the control of salt tolerance

One of the essential elements that is involved in the control of salt tolerance is calcium. If calcium is readily available plants are better able to maintain homoeostasis in saltier environments. It is the ratio of cytosolic to internal calcium that is important to the regulation of salt sensitivity. Calcium ions are also able to help with ion toxicity by maintaining potassium transport mechanisms and the selectivity of potassium to sodium uptake in areas of high salinity.