Number of genes differentially expressed in roots under saline-alkaline stress treatment. Total number of genes differentially up- (green bars) and down-regulated (yellow bars) in roots under 50 mmol/L NaHCO3 stress treatment compared with the sample without stress (P < 0.05, q < 0.15). The x-axis represents hours of stress. The y-axis represents number of probe sets. The tissues for RNA extraction were harvested at the indicated time points. See Methods for data normalization, processing, statistical analysis and classification of differentially expressed genes.