Two-dimensional electrophoresis is a powerful tool to explore the plant proteome and to unravel changes in protein expression between samples. However, the acquisition of images on which thousands of spots may be resolved has some weak points, as always pointed out by scientists working with gel-free techniques, such as the lack of reproducibility. Nowadays, this inconvenience can be bypassed by the use of a technique known as "difference gel electrophoresis" or DIGE. This technique requires the labelling of proteins by fluorochromes before their separation on 2DE gels. This technique may be applied to a wide array of plant stress studies. Providing accurate quantitative results, differentially abundant spots are usually subjected to tryptic digestion and identified using electrospray ionization, matrix-assisted laser desorption/ionization-time of flight-MS and/or tandem MS.