Proteomic and histological analyses of endosperm development in Cyclamen persicum as a basis for optimization of somatic embryogenesis

The endosperm plays an important role for the development of zygotic embryos, while somatic embryos lack a seed coat and endosperm and often show physiological disorders. This study aims at elucidating the cellular and physiological processes within the endosperm of the ornamental species Cyclamen persicum Mill. Histological analyses were performed from 0 to 11 weeks after pollination (WAP). At 3 WAP, a syncytium was clearly visible with a globular zygotic embryo. From 4 WAP, cellularization of the endosperm, at 5 WAP a small torpedo shaped embryo, and from 7 WAP cell expansion was observed. By 11 WAP the endosperm appeared fully differentiated. Total soluble proteins were extracted from the endosperm at 4, 5, 7, 9 and 11 WAP and resolved using two dimensional isoelectric focussing/sodium dodecyl sulphate-polyacrylamide gel electrophoresis (2D IEF/SDS-PAGE). A shift from high-molecular-mass proteins to low-molecular-mass proteins during endosperm development was observed. A total of 1137 protein spots/gel were detected in the three protein fractions extracted at 7, 9 and 11 WAP. Mass spectrometry analysis of the 48 predominant protein spots in endosperm at 7, 9 and 11 WAP resulted in the identification of 62 proteins, ten of which were described for the first time in Cyclamen. Additionally, 186 proteins were identified using the C. persicum embryo proteome reference map. Proteins involved in abscisic acid signalling and oxidative stress responsive proteins were found to be important for seed development in Cyclamen. The new insights into endosperm physiology including storage compounds are discussed.

Highlights► Key stages in endosperm development identified in Cyclamen persicum. ► Shift from high- to low-molecular-mass proteins during endosperm development. ► Abscisic acid signalling and antioxidant-responsive proteins play an important role. ► Lipids, xyloglucans and proteins identified as Cyclamen seed storage compounds.