Proteomic identification of an hsp70.1 protein induced in Arabidopsis cells following hyperosmotic stress treatments

We demonstrate that treatments with NaCl and the non-ionic osmoticum sorbitol cause acidification in the extracellular medium in Arabidopsis thaliana cell suspension cultures, a typical hyperosmotic stress response in plants. We also show that when administered for 96 hours at equi-osmolar concentrations, sorbitol, unlike NaCl, was not lethal to Arabidopsis cells. A combination of [³⁵S]methionine/cysteine radiolabelling, 2-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ ionization-time of flight (Maldi-Tof) mass spectrometry revealed that the abundance of heat shock protein (hsp) 70.1 increased as a result of both sorbitol and NaCl treatments in Arabidopsis. This novel finding, resulting from the first proteomics analysis of NaCl-and sorbitol-stressed Arabidopsis, is interpreted and discussed in the light of what we know of the osmoprotective role of hsp70.1 in animal and microbial systems.