In order to use the P5 isoform as a marker of somatic embryo-genesis, we isolated and identified this isoenzyme. The band was digested with trypsin and the “peptide fingerprint” was obtained by analysis of the resulting mixture by matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry,where we observed a large number of peaks indicating that therewas a large amount of peptides in the band. Accordingly, we thenanalyzed the band using LTQ mass spectrometer in order to increasethe likelihood of identification.