Comparative proteomic analysis of tomato (Solanum lycopersicum) leaves under salinity stress

Salinity is a major constraint to crop productivity. The mechanisms responsible for the effects of salt stress on tomato plants were examined by means of proteomic analysis. Two contrasting tomato genotypes (cv. Roma and cv. SuperMarmande) seedlings were cultivated using a hydroponic system in the controlled environment growth chamber. The salt stress (NaCl) was applied (0, 100 and 200 mM) and maintained for 14 days. Leaf osmotic potential significantly decreased with NaCl treatment in genotype SuperMarmande. However, genotype Roma maintained its leaf osmotic adjustment under salt treatment. Lipid peroxidation (estimated by MDA content) significantly increased under salt in both cultivars, but the rate of increment was higher in genotype SuperMarmande. Leaves of control and salt-stressed plants were also sampled for phenol protein extraction. Proteins were separated by two-dimensional gel electrophoresis (2-DE). 26 protein spots exhibited significant abundance variations between samples. Our results indicated that some proteins exhibited variation strictly related to salt stress whatever the genotype, while some other proteins also showed variation which could be related to the degrees of genotype tolerance. The up-regulation of Rubisco activases and RuBisCO large subunit under salt treatment, was correlated with an increase in abundance level of proteins that are involved in energy metabolism (pyruvate dehydrogenase, Glucose-6-phosphate dehydrogenase, Malate dehydrogenase), especially in salt-tolerant genotype (Roma). Accumulation of antioxidants enzymes (ascorbate peroxidase, glutathione peroxidase, peroxidase and mitochondrial peroxiredoxin) in the leaves of salt tolerant genotype (Roma) was well correlated with the level of lipid peroxidation of membranes. Up-regulation of Heat Shock Proteins and maintenance of water status as reflected by leaf osmotic potential are considered to be strongly correlated with to the degrees of tomato genotype tolerance in this study.