Plant biology: The salty tale of Arabidopsis

Most angiosperms — and all major crops — are unable to withstand high concentrations of sodium chloride. Soils containing concentrations of salt amounting to a few hundred millimolar occur naturally, of course, and saline land is estimated to represent between 2.3 and 6.4% of global land surface [1]. As much as 13% of cultivated land is thought to be salt-affected. In some instances, however, agricultural activity is increasing this proportion because salts dissolved in irrigation water are left in the soil after evapo-transpiration. The problem is particularly marked in arid and semi-arid regions of the world, where it is estimated that some 10 million hectares of land are abandoned annually as a result of increasing salinization [2]. There are, nevertheless, angiosperm species which are tolerant to salt, and some even grow in sea water. It has long been recognised that salt tolerance is a multigenic trait, requiring at least capacity for osmotic adjustment, for synthesis of compatible solutes (osmoprotectants) to retain the water potential of the cytosol, and for effective exclusion of salt or for its intracellular compartmentation. Many salt-tolerant plants exhibit additional morphological adaptations — for example, specialized bladder cells for accumulation of salt or glands for salt excretion. A genetic dissection of salt tolerance therefore appears at first sight to be a daunting task, especially as most well-studied model species are not particularly tolerant of salt.