Increased gelling agent concentration promotes somatic embryo maturation in hybrid larch (Larix × eurolepsis): a 2-DE proteomic analysis.

An integrated physiological and proteomic approach was used to investigate the effects of high gellan gum concentration in the medium during maturation of somatic embryos (SE) of hybrid larch, by comparing embryos incubated in media with a high gellan gum concentration (8 g l(-1) ) and the standard concentration (4 g l(-1) ) after 1, 3, 6 and 8 weeks of maturation. Because of the reduced availability of water in the 8 g l(-1) medium, the cultured embryos had a lower osmotic water potential (Ψπ) and water contents, but higher dry weights (DWs), at 8 weeks compared with embryos cultured on the standard medium. The high gellan gum concentration induced a desiccation that is characteristic in zygotic embryo maturation. Total soluble proteins were extracted from SE with trichloroacetic acid (TCA)-acetone after 1 and 8 weeks of maturation on media with 4 and 8 g l(-1) of gellan gum, and separated by two-dimensional gel electrophoresis (2-DE) at pH 4-7. More than 1100 proteins were reproducibly detected on each gel. At 1 and 8 weeks respectively, the abundances of 62 and 49 spots detected in analyses of embryos matured at the two gellan gum concentrations, significantly differed. Among 62 significantly differing spots at 1 week of maturation, the corresponding proteins of 56 were reliably identified by liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS), and were found to be mainly involved in 'carbohydrate metabolism', 'genetic information processing' or 'environmental information processing' according to kegg taxonomy. Both physiological parameters and the proteins identified suggested that the embryos were stressed when they were cultured on 4 g l(-1) of gellan gum.