Protein pattern changes in tomato under in vitro salt stress

The investigation of salt-induced changes in the proteome would highlight important genes because of a high resolution of protein separation by two-dimensional gel electrophoresis (2-DE) and protein identification by mass spectrometry and database search. Tomato ( Lycopersicon esculentum Mill.) is a model plant for studying the mechanisms of plant salt tolerance. Seeds of tomato cv. Shirazy were germinated on water-agar medium. After germination, seedlings were transferred to Murashige and Skoog nutrient medium supplemented with 0, 40, 80, 120, and 160 mM NaCl. After 24 days, leaf and root samples were collected for protein extraction and shoot dry weight measurement. Alterations induced in leaf and root proteins under salt stress treatments were studied by one-dimensional SDS-PAGE. Leaf proteins were also analyzed by 2-DE. With increasing salt concentration in the medium, shoot dry weight decreased. SDS-PAGE showed induction of at least five proteins with mol wts of 30, 62, and 75 kD in roots and 38 and 46 kD in leaves. On the 2-DE gel, more than 400 protein spots were reproducibly detected. At least 18 spots showed significant changes under salt stress. Three of them corresponded to new proteins, while six proteins were up-regulated and five proteins were down-regulated by salt stress. In addition, salinity inhibited the synthesis of four leaf proteins. Ten spots were analyzed by matrix-assistant laser desorption/ionization-time of flight (MALDI-TOF), which led to the identification of some proteins, which could play a physiological role under salt stress. The expression of new proteins(enoyl-CoA hydratase, EGF receptor-like protein, salt tolerance protein, phosphoglycerate mutase-like protein, and M2D3.3 protein) under salt stress indicates that tomato leaf cells respond to salt stress by changes in different physiological processes. All identified proteins are somehow related to various salt stress responses, such as cell proliferation.