To understand metabolic modifications in plants under salt stress, the physiological and biochemical responses of cucumber (Cucumis sativus L. cv. Jinchun No. 2) seedlings to salt stress was investigated. The dry weight and fresh weight of cucumber seedling roots were significantly reduced by treatment with NaCl; Na(+) and Cl(-) were increased, while K(+) and K(+)/Na(+) ratio were decreased. To identify components of salt stress signaling, we compared the high resolution two-dimensional gel electrophoresis (2-DE) protein profiles of control and NaCl-treated roots, and the intensity of 34 protein spots varied. Of these spots, the identities of 29 (21 up-regulated and 8 down-regulated protein spots induced after salt stress) were determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) and liquid chromatography electro-spray ionization tandem mass spectrometry (LC-ESI-MS/MS). The majority of the proteins had functions related to metabolism, energy and transport, and are involved in regulating reactions and defending against stress. A semi-quantitative reverse transcriptional-polymerase chain reaction (PCR) approach based on peptide sequences was used to compare transcript and protein accumulation patterns for 10 candidate proteins. Of these proteins, 8 patterns of induced transcript accumulation were consistent with those of induced protein accumulation. It is therefore likely that the response of the plant's proteome to NaCl stress is complex, and that the identified proteins may play an important role in regulating adaptation activities following exposure to NaCl stress in order to facilitate ion homeostasis.
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