LEAF PROTEOME ANALYSIS SIGNIFIED THAT PHOTOSYNTHESIS AND ANTIOXIDANTS ARE KEY INDICATORS OF SALINITY TOLERANCE IN CANOLA (BRASSICA NAPUS L.)

Growth and yield reduction in different crops including canola is predicted to rise due to salinity stress in coming years. Understanding responses to salt stress will help in selecting and breeding salt tolerant canola cultivars. Physiological and leaf proteomic responses of 13 cultivars of canola were investigated under salt stress. In a pot experiment, three-week-old plants were grown under normal or salt stress (150 mM NaCl) for further two weeks. Out of 13 canola cultivars, cvs DGL, Dunkled, Faisal Canola and Punjab Canola were categorized as salinity stress tolerant cultivars, while cvs Bulbul-98, Oscar, Legend and Cyclone were considered as salt sensitive. Wide genotypic variations in canola cultivars have been observed in accumulation of potassium and sodium ions in the leaves and roots. Salt tolerant cultivars accumulated low Na+ in their leaves than in in roots indicating limited uptake of Na+ at root level with subsequent its transport to shoot. Moreover, salt tolerant cultivars had greater Na+ discriminating capacity against K+. Salt tolerant cultivars were higher in leaf relative water content. Although Fv/Fm did not change in canola cultivars due to salt stress, Fv/Fo and PIABS decreased considerably in all cultivars indicating important indicators of salt stress. Salt stress increased V-j, V-I, ABS/RC, TRo/RC and DIo/RC but it decreased ETo/RC which indicated that salt stress damaged the donor end of PSII (oxygen evolving complex) and reaction centers. Such adverse effects were maximal in salt sensitive cultivar Legend while minimal effects were observed in salt tolerant canola cultivars Faisal Canola, DGL and Dunkled. From comparative proteome analysis, it is obvious that 18 differentially expressed proteins in canola cultivars are mainly related with antioxidative defense system, photosynthesis and gene regulation. In addition, expression of these proteins was greater in salt tolerant cultivars. Cellular enegetics related proteins were downregulated particularly in salt sensitive cultivars due to salt stress. It is concluded that antioxidative defence system and photosynthesis are major componens of salt tolerance in canola in addition to salt exclusion. In addition, physiological studies complemented with proteomics will help in understanding detailed mechanism of salt tolerance.