Comparative Proteomic Analysis of Responses to Salt Stress in Chinese Willow (Salix matsudana Koidz)

Salinity in soils is among the major constraints of agricultural and forestry productivity worldwide. To investigate the basis of salt tolerance in Salix matsudana Koidz (Chinese willow), comparative proteomes of 1.5-month-old cuttings were analyzed using two-dimensional gel electrophoresis (2-DE). Proteins were extracted from roots of plants grown under 100 mM NaCl stress for 6, 24, or 48 h; whereas proteins from stems and leaves were extracted from plants grown under 100 mM NaCl stress for a period of 48 h. In total, 42, 17 and 19 differential protein spots were identified by MALDI-TOF/TOF in roots, stems and leaves, respectively. The majority of these salt stress-responsive proteins were organ specific. The identified proteins were involved in 12 metabolic pathways and processes, and quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis revealed that some of the proteins, such as USP-like, PR-10 and quinone reductase, were regulated by salt stress at the level of transcription. Pathogenesis-related proteins, in particular, were found to be abundant and up-regulated by salt stress. This suggests that PRs may be closely related to S. matsudana defense against salt stress, possibly by enhancing the resistance to opportunistic fungal attack. Based on the predicted functions of the identified proteins, we propose a salt stress response model describing a possible management strategy for cellular activities in S. matsudana under short-term salinity stress. Furthermore, some of the identified proteins might be potential candidates to improve salt tolerance in woody plants.