Changes in Protein Synthesis and Phosphorylation during Microspore Embryogenesis in Brassica napus

Changes in protein synthesis and phosphorylation during microspore embryogenesis in Brassica napus were investigated by two-dimensional (2-D) gel electrophoresis. The expression pattern of 6 proteins previously identified as putative markers for embryo initiation in microspore cultures (Cordewener et al., 1994), was studied during later stages of embryo development. All of them were transiently expressed for the induction period (8 h to 2 days) and disappeared on the 5th day but two of them were expressed again at the later stage of embryogenesis (12th day). Major changes in the patterns of protein synthesis were observed 5 days after initiation of microspore embryogenesis. In this period of time embryogenic microspores have formed proembryos within their exine. Later stages ofembryo development were not accompanied by major changes in 2-D protein patterns. Comparison of 2-D patterns of phosphorylated proteins revealed minor differences between embryogenic and non-embryogenic cultures, except for the level of phosphorylation of hsp70. A clear difference of extracellular secreted proteins was observed between embryogenic and non-embryogenic microspore cultures. This work provides a biochemical insight for the understanding of microspore embryogenesis at the protein level.