Differential gene expression during somatic embryogenesis in <i>Digitalis Ianata</i> analyzed by <i>in vivo</i> and <i>in vitro</i> protein synthesis

Abstract

Summary During somatic embryogenesis in Digitalis Ianata , proembryogenic masses (PEMs) develop into globular‐, heart‐ and torpedo‐shaped embryos. The morphogenesis is correlated with drastic alterations in the composition of cellular and extracellular polypeptides. By comparing the spectra of in vivo translated polypeptides after two‐dimensional gel electrophoresis, three main classes of polypeptides were distinguished: (i) decreasing proteins; (ii) increasing proteins; (iii) constitutive polypeptides. Distinct subclasses of PEM‐ and embryo‐specific proteins could be discerned. The embryo‐specific polypeptides reached the highest relative prevalence in either the globular‐, heart‐ or torpedo‐shaped embryos and were not expressed in a non‐embryogenic cell line of D. Ianata , strain 119, indicating their temporally defined and embryogenesis‐related pattern of expression. The alterations of protein synthesis did not correlate with corresponding changes in the spectrum of abundant in vitro ‐translatable mRNAs. Relatively few PEM‐and embryo‐specific mRNAs could be discerned from constitutive messengers suggesting a posttranscriptional mode of control for the majority of protein genes during embryogenesis. However, for those in vitro synthesized (homologous) polypeptides which had a counterpart of identical isoelectric point and relative molecular mass among the in vivo translated polypeptides, a transcriptional type of gene expression was implied, since the mRNA content and the in vivo rate of protein synthesis changed similarly.