Extraction of proteins from A. thaliana hypocotyls with salts. A – Half of the CW4 lyophilized powder (0.65 g) was successively suspended in 0.2 M CaCl2, 5 mM acetate buffer pH 4.6, and in 2 M LiCl, 5 mM acetate buffer pH 4.6. The CaCl2 extract contained 400 μg of proteins. The LiCl extract contained 40 μg of proteins. B – Number of proteins identified in each extract after 1D-GE separation, and analysis by MALDI-TOF MS or LC-MS/MS. Proteins were classified as indicated in legend to Figure 1. Seventy-three different proteins predicted to be secreted were identified in this study (see Additional file 4).