Salt stress causes changes in root apoplastic barriers, such as the endodermis and the exodermis, and these changes are associated with variation in abiotic stress tolerance. We explored variation in root apoplastic barrier traits, O2 consumption and root and shoot Na+ and K+ content in a diverse collection of commercial and wild barley accessions subjected to non-saline (control) and saline treatments. Lignin and suberin deposition in endo- and exo-dermal cell walls varied between the accessions and in response to salt treatments. Twenty-two wild barley accessions formed an exodermis in response to salt treatments, whereas the commercial barley cultivar Barke did not develop an obvious exodermis. Accessions with pronounced root barrier deposition tended to have lower O2 consumption relative to the accessions with less obvious barriers. Treatment with abscisic acid enhanced suberisation and lead to a pronounced formation of an exodermis in wild barley accessions, whereas treatment with an ethylene precursor had no obvious effect on suberisation. Principal component analysis revealed associations between suberin deposition, root and shoot Na+ and K+, and root respiration. The variation in root apoplastic barrier traits within the barley accessions represents a useful resource for future crop breeding to improve environmental stress tolerance.

The phosphorylation states of two serine residues within the C-terminal domain of AtPIP2;1 (S280, S283) regulate its trafficking to the plasma membrane in response to salt and osmotic stress. Here we investigated whether the phosphorylation states of S280 and S283 also influence AtPIP2;1 facilitated water and cation transport. A series of single and double S280 and S283 phospho-mimic and -deficient AtPIP2;1 mutants were tested in heterologous systems. In Xenopus laevis oocytes, phospho-mimic mutants AtPIP2;1 S280D, S283D and S280D/S283D, had significantly greater ion conductance for Na+ and K+, whereas the S280A single and S280A/S283A double mutants, had greater water permeability. A phospho-mimic-dependent inverse relationship between AtPIP2;1 water and ion transport with a 10-fold change in both was observed. These results revealed that phosphorylation of S280 and S283 influences the preferential facilitation between ion and water permeability by AtPIP2;1. The results also hint at other sites playing a role that are yet to be elucidated. Expression of the phospho-mimic AtPIP2;1 mutants in Saccharomyces cerevisiae, confirmed that phosphorylation influences plasma membrane localisation, and revealed higher Na+ accumulation for S280A and S283D. Collectively, the results show that phosphorylation in the C-terminal domain of AtPIP2;1 influences its subcellular localisation and cation transport capacity.