Physiological and Proteomic Analysis of Brassica napus in Response to Salt Stress

Salinity is a major abiotic stress that adversely affects plant growth and development. Canola (Brassica napus L.) is an important oilseed crop in the world, and its yield decreases drastically with increasing salinity. To date, little is known about the molecular mechanisms underlying its salt stress response and tolerance. This study combines physiological assays with comparative proteomics to understand how B. napus plants respond to salt stress. The changes in relative water content, electrical conductance, stomata conductance, intercellular CO2 concentration, transpiration rate, photosynthesis rate, water usage efficiency, respiration rate, chlorophyll fluorescence, antioxidant enzyme activities, soluble sugar, proline and betaine in B. napus plants under different NaCl concentrations were analyzed. Proteomic profiles of B. napus plants under 100, 200 and 400 mM NaCl treatment at 7 day and 14 day were acquired using iTRAQ LC-MS/MS based quantitative proteomics. A total of 2316 proteins were identified in B. napus leaves, of which 614 proteins showed differential expression under salt stress. These proteins were mainly involved in 10 processes, of which proteins in stress and defense, metabolism and photosynthesis pathways ranked the top three. Subcellular localization analysis showed that most proteins were located in chloroplast, cytoplasm, mitochondria and nucleus. A total of 138 differentially expressed proteins were predicted to interact with each other. These results have provided a comprehensive view of the physiological and molecular processes taken place in B. napus leaves under salt stress, and revealed the molecular mechanisms underlying salt tolerance of B. napus plants.