Because salt stress is a major abiotic source of stress on potato crops, the molecular mechanism of the response of potato plants to salt stress was examined. On exposure to salt, the salt-sensitive cultivar Concord showed a greater reduction in shoot and root length than did the salt-tolerant cultivar Kennebec. For both cultivars, the reduction in the length of shoots was more severe than that of the roots. Salt exposure increased the content of free proline and total soluble sugars in shoots of Kennebec; these remained unchanged in Concord. Proteins extracted from shoots of both cultivars exposed to 90 mM NaCl were separated by two-dimensional polyacrylamide gel electrophoresis: 322 and 305 proteins were detected in shoots of Kennebec and Concord, respectively. Of these, 47 proteins were differentially expressed under NaCl treatment in shoot of both cultivars. Among the differentially expressed proteins, photosynthesis- and protein-synthesis-related proteins were drastically down-regulated, whereas osmotine-like proteins, TSI-1 protein, heat-shock proteins, protein inhibitors, calreticulin, and five novel proteins were markedly up-regulated. These results suggest that up-regulation of defense-associated proteins may confer relative salt tolerance to potato plants.

To evaluate the response of soybean to salt stress, the related changes in protein expression were investigated using the proteomic approach. Soybean plants were exposed to 0, 50, 100, and 200 mM NaCl. Especially at 200 mM, the length and fresh weight of the hypocotyl and root reduced under salt stress, while the proline content increased. Proteins from the hypocotyl and root treated with 100 mM NaCl were extracted and separated by two-dimensional polyacrylamide gel electrophoresis; 321 protein spots were detected. In response to salt stress, seven proteins were reproducibly found to be up- or down-regulated by two to sevenfold: late embryogenesis-abundant protein, beta-conglycinin, elicitor peptide three precursor, and basic/helix-loop-helix protein were up-regulated, while protease inhibitor, lectin, and stem 31-kDa glycoprotein precursor were down-regulated. These results indicate that salinity can change the expression level of some special proteins in the hypocotyl and root of soybean that may in turn play a role in the adaptation to saline conditions.

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To understand the response of potato to salt stress, antioxidant enzyme activities and ion content were analyzed for a sensitive and a tolerant cultivar. Nodal cuttings of the tolerant cultivar, Kennebec, and the sensitive cultivar, Concord, were exposed to media without or with 30, 60, 90 or 120 mmol/L NaCl for 4 weeks. On exposure to NaCl, the length and fresh and dry weight of both shoots and roots of Concord showed greater decrease than those of Kennebec. The decrease in shoot growth was more severe than that of the root for both cultivars. The K(+) content of shoots and roots of both cultivars was reduced in a dose-dependent manner by exposure to NaCl; the Na(+) content increased. Activities of ascorbate peroxidase, catalase and glutathione reductase were increased in NaCl-exposed shoots of Kennebec; the corresponding activities in NaCl-exposed shoots of Concord were decreased. Roots of both cultivars showed similar changes in the activities of these enzymes on exposure to NaCl. These studies established that enzyme activities in Concord shoots are inversely related to the NaCl concentration, whereas those in Kennebec do not show a dose dependency, which is also the case for the roots of both cultivars. Our findings suggest that an increase in activity of antioxidant enzymes, such as ascorbate peroxidase, catalase and glutathione reductase, can contribute to salt tolerance in Kennebec, a salt resistant cultivar of potato.

Increasing of world population marks a serious need to create new crop cultivars and medicinal plants with high growth and production at any environmental situations. Among the environmental unfavorable conditions, salinity is the most widespread in the world. Crop production and growth severely decreases under salt stress; however, some crop cultivars show significant tolerance against the negative effects of salinity. Among salt stress responses of crops, proteomic responses play a pivotal role in their ability to cope with it and have become the main center of notification. Many physiological responses are detectable in terms of protein increase and decrease even before physiological responses take place. Thus proteomic approach makes a short cut in the way of inferring how crops response to salt stress. Nowadays many salt-responsive proteins such as heat shock proteins, pathogen-related proteins, protein kinases, ascorbate peroxidase, osmotin, ornithine decarboxylase, and some transcription factors, have been detected in some major crops which are thought to give them the ability of withstanding against salt stress. Proteomic analysis of medicinal plants also revealed that alkaloid biosynthesis related proteins such as tryptophan synthase, codeinone reductase, strictosidine synthase, and 12-oxophytodienoate reductase might have major role in production of secondary metabolites. In this review we are comparing some different or similar proteomic responses of several crops and medicinal plants to salt stress and discuss about the future prospects.

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