Efficient leaf solute partioning in Salicornia fruticosa allows growth under salinity

Abstract

The halophyte Salicornia fruticosa is able to tolerate a wide range of salinity. Since the cellular distribution of ions and solutes within leaves can be linked to the mechanisms to cope with salt stress, the aim of this work was to stablish the relation between the solute gradient along S. fruticosa leaves, distinguishing two parts: leaf base and apex, and the physiological parameters involved in response to distinct salt levels. For that, plants were grown at 0, 100, 200 and 300 mM NaCl, and plant growth, leaf gas exchange parameters and water status were measured as well as leaf ion and metabolite content. Also, their relation with the transcript levels of the NHX1 antiporter and PIP1 and TIP aquaporins was determined. Plant growth was optimal at 200 mM NaCl and was decreased at 300 mM. At 200 mM NaCl, these proteins play an important role in leaf growth through a differential Na and water partitioning between the leaf base and apex that regulates a progressive leaf solute gradient. At 300 mM NaCl, no differential expression of NHX and aquaporins in both parts of the leaf was found. However, the transcript levels were elevated according to an increased vacuolar osmotic pressure and a high organic solute content in the cytosol. At the individual level distinct malic acid and glucose partitioning was observed. All the data indicated that NHX and the aquaporins PIP and TIP exerted a dual function according to the salt intensity and are involved in the regulation of leaf solute partitioning; this could be useful in order to estimate plant availability for Na+ accumulation in a further bioremediation study. All the data indicated that leaf solute partitioning depended on salt intensity where NHX and the aquaporins PIP and TIP exerted an important and dual function favouring a different Na and water distribution in the leaf cells. This could be useful in order to estimate plant availability for Na+ accumulation in a further bioremediation study.